Glen Hartman, Research Plant Pathologist, USDA-ARS

Email: ghartman@illinois.edu
Phone: (217) 244-3258

Research Focus

I have been involved with plant pathology research and disease control strategies since 1977 when I attended the University of Minnesota as an undergraduate in the plant pathology department. During my professional career I have lived in North Dakota, Illinois, Zambia, Nigeria, and Taiwan. I have visited over 20 countries professionally and have participated in many international and regional meetings.

The long-term goal of my program is to conceive and conduct applied and basic research in three areas of soybean pathology that will aid in efficient disease control strategies: 1) research on the biology and ecology of soybean pathogens with emphasis on their pathogenic variation, 2) the study of basic epidemiological concepts related to disease development and spread and how pathogens and the diseases they cause affect the quality and quantity of soybean yields, and 3) investigating the existence, nature and genetics of host resistance in soybean germplasm and in other Glycine species.

PUBLICATIONS:

• 2016: Rincker, K., Hartman, G. L., and Diers, B. W. 2016. Fine mapping of resistance genes from five brown stem rot resistance sources in soybean. The Plant Genome 9:doi: 10.3835/plantgenome2015.3808.0063. [link] [view abstract]
  Brown stem rot (BSR) of soybean [Glycine max (L.) Merr.] caused by Cadophora gregata (Allington & Chamb.) T.C. Harr. & McNew can be controlled effectively with genetic host resistance. Three BSR resistance genes Rbs1, Rbs2, and Rbs3, have been identified and mapped to a large region on chromosome 16. Marker-assisted selection (MAS) will be more efficient and gene cloning will be facilitated with a narrowed genomic interval containing an Rbs gene. The objective of this study was to fine map the positions of Rbs genes from five sources. Mapping populations were developed by crossing the resistant sources ‘Bell’, PI 84946-2, PI 437833, PI 437970, L84-5873, and PI 86150 with either the susceptible cultivar Colfax or Century 84. Plants identified as having a recombination event near Rbs genes were selected and individually harvested to create recombinant lines. Progeny from recombinant lines were tested in a C. gregata root-dip assay and evaluated for foliar and stem BSR symptom development. Overall, 4878 plants were screened for recombination, and progeny from 52 recombinant plants were evaluated with simple-sequence repeat (SSR) genetic markers and assessed for symptom development. Brown stem rot resistance was mapped to intervals ranging from 0.34 to 0.04 Mb in the different sources. In all sources, resistance was fine mapped to intervals inclusive of BARCSOYSSR_16_1114 and BARCSOYSSR_16_1115, which provides further evidence that one locus provides BSR resistance in soybean.
  
  
  
• 2016: Hartman, G., Pawlowski, M. L., Herman, T., and Eastburn, D. M. 2016. Organically grown soybean production in the USA: Constraints and management of pathogens and insect pests. Agronomy 2016, 6(1), 16; doi:10.3390/agronomy6010016. [link] [view abstract]
  Soybean is the most produced and consumed oil seed crop worldwide. In 2013, 226 million metric tons were produced in over 70 countries. Organically produced soybean represents less than 0.1% of total world production. In the USA, the certified organic soybean crop was grown on 53 thousand ha or 0.17% of the total soybean acreage in the USA (32 million ha) in 2011. A gradual increase in production of organically grown soybean has occurred since the inception of organic labeling due to increased human consumption of soy products and increased demand for organic soybean meal to produce organic animal products. Production constraints caused by pathogens and insect pests are often similar in organic and non-organic soybean production, but management between the two systems often differs. In general, the non-organic, grain-type soybean crop are genetically modified higher-yielding cultivars, often with disease and pest resistance, and are grown with the use of synthetic pesticides. The higher value of organically produced soybean makes production of the crop an attractive option to some farmers. This article reviews production and uses of organically grown soybean in the USA, potential constraints to production caused by pathogens and insect pests, and management practices used to reduce the impact of these constraints.
  
  
  
• 2016: Pawlowski, M., Bowen, C., Hill, C. B., and Hartman, G. L. 2016. Responses of soybean genotypes to pathogen infection after the application of elicitors. Crop Protection 87:78-84. [link] [view abstract]
  Soybean diseases and pests can affect soybean production. One emerging pest management method is to treat plants with chemical elicitors at nontoxic levels to induce host resistance. The objective of this research was to determine if elicitors, benzothiadiazole (BTH), chitosan (CHT), phenylalanine (PHE), and salicylic acid (SA), applied to soybean foliage could alter the response of soybean genotypes to soybean pathogens. Two of the soybean genotypes had been previously shown to produce high or low amounts of reactive oxygen species (ROS) in response to elicitation. In the greenhouse, soybean genotypes were challenged with three pathogens 48 h after elicitation. Plants of the cultivar Pharaoh (susceptible control) treated with SA, and then inoculated with Macrophomina phaseolina had a shorter (α = 0.05) stem lesion length (34 mm) than the water control (55 mm). Plants of soybean genotype LD00-2817p (high capacity to produce ROS) and the cultivar Sloan treated with BTH, PHE, or SA, and then inoculated with Phytophthora sojae had greater (α = 0.05) survival rates than plants treated with the water control. The four elicitors and a water control were evaluated on LD00-2817p and LDX01-1-65 in the field for two consecutive years. Foliar disease incidence and severity were low for both years, although there were some differences in stem disease ratings. For example, charcoal rot stem severity rating was reduced (α = 0.05) from 2.0 in the water control to 1.1 with a PHE treatment for LD00-2817p and was reduced (α = 0.05) from 3.8 in the water control to 2.6 with SA for LDX01-1-65 in 2013. Both greenhouse controlled experiments and field experiments showed that genotype-specific elicitation reduced disease severity in some cases, but the differences were greater under controlled-inoculated conditions.
  
  
  
• 2016: Chang, H.-X., Domier, L. L., Radwan, O., Yendrek, C. R., Hudson, M. E., and Hartman, G. 2016. Identification of multiple phytotoxins produced by Fusarium virguliforme including a phytotoxic effector (FvNIS1) associated with soybean sudden death syndrome foliar symptoms. Molecular Plant-Microbe Interactions 96:96-108. [link] [view abstract]
  Sudden death syndrome (SDS) of soybean is caused by a soilborne pathogen, Fusarium virguliforme. Phytotoxins produced by F. virguliforme are translocated from infected roots to leaves, in which they cause SDS foliar symptoms. In this study, additional putative phytotoxins of F. virguliforme were identified, including three secondary metabolites and 11 effectors. While citrinin, fusaric acid, and radicicol induced foliar chlorosis and wilting, Soybean mosaic virus (SMV)-mediated overexpression of F. virguliforme necrosis-inducing secreted protein 1 (FvNIS1) induced SDS foliar symptoms that mimicked the development of foliar symptoms in the field. The expression level of fvnis1 remained steady over time, although foliar symptoms were delayed compared with the expression levels. SMV::FvNIS1 also displayed genotype-specific toxicity to which 75 of 80 soybean cultivars were susceptible. Genome-wide association mapping further identified three single nucleotide polymorphisms at two loci, where three leucine-rich repeat receptor-like protein kinase (LRR-RLK) genes were found. Culture filtrates of fvnis1 knockout mutants displayed a mild reduction in phytotoxicity, indicating that FvNIS1 is one of the phytotoxins responsible for SDS foliar symptoms and may contribute to the quantitative susceptibility of soybean by interacting with the LRR-RLK genes.
  
  
  
• 2016: Chang, H.-X., Yendrek, C. R., Caetano-Anollés, G., and Hartman, G. 2016. Genomic characterization of plant cell wall degrading enzymes and in silico analysis of xylanses and polygalacturonases of Fusarium virguliforme. BMC Microbiology 16:147 DOI: 10.1186/s12866-016-0761-0. [link] [view abstract]
  Plant cell wall degrading enzymes (PCWDEs) are a subset of carbohydrate-active enzymes (CAZy) produced by plant pathogens to degrade plant cell walls. To counteract PCWDEs, plants release PCWDEs inhibitor proteins (PIPs) to reduce their impact. Several transgenic plants expressing exogenous PIPs that interact with fungal glycoside hydrolase (GH)11-type xylanases or GH28-type polygalacturonase (PG) have been shown to enhance disease resistance. However, many plant pathogenic Fusarium species were reported to escape PIPs inhibition. Fusarium virguliforme is a soilborne pathogen that causes soybean sudden death syndrome (SDS). Although the genome of F. virguliformewas sequenced, there were limited studies focused on the PCWDEs of F. virguliforme. Our goal was to understand the genomic CAZy structure of F. viguliforme, and determine if exogenous PIPs could be theoretically used in soybean to enhance resistance against F. virguliforme. Results F. virguliforme produces diverse CAZy to degrade cellulose and pectin, similar to other necrotorphic and hemibiotrophic plant pathogenic fungi. However, some common CAZy of plant pathogenic fungi that catalyze hemicellulose, such as GH29, GH30, GH44, GH54, GH62, and GH67, were deficient in F. virguliforme. While the absence of these CAZy families might be complemented by other hemicellulases, F. virguliforme contained unique families including GH131, polysaccharide lyase (PL) 9, PL20, and PL22 that were not reported in other plant pathogenic fungi or oomycetes. Sequence analysis revealed two GH11 xylanases of F. virguliforme, FvXyn11A and FvXyn11B, have conserved residues that allow xylanase inhibitor protein I (XIP-I) binding. Structural modeling suggested that FvXyn11A and FvXyn11B could be blocked by XIP-I that serves as good candidate for developing transgenic soybeans. In contrast, one GH28 PG, FvPG2, contains an amino acid substitution that is potentially incompatible with the bean polygalacturonase-inhibitor protein II (PvPGIP2). Conclusions Identification and annotation of CAZy provided advanced understanding of genomic composition of PCWDEs in F. virguliforme. Sequence and structural analyses of FvXyn11A and FvXyn11B suggested both xylanases were conserved in residues that allow XIP-I inhibition, and expression of both xylanases were detected during soybean roots infection. We postulate that a transgenic soybean expressing wheat XIP-I may be useful for developing root rot resistance to F. virguliforme.
  
  
  
• 2016: Chang, H.-X., Brown, P., Lipka, A., Domier, L. L., and Hartman, G. L. 2016. Genome-wide association and genomic prediction identifies associated loci and predicts the sensitivity of Tobacco ringspot virus in soybean plant introductions. BMC Genomics 17:153:DOI 10.1186/s12864-12016-12487-12867. [link] [view abstract]
  Background Genome-wide association study (GWAS) is a useful tool for detecting and characterizing traits of interest including those associated with disease resistance in soybean. The availability of 50,000 single nucleotide polymorphism (SNP) markers (SoySNP50K iSelect BeadChip; www.soybase.org) on 19,652 soybean and wild soybean plant introductions (PIs) in the USDA Soybean Germplasm Collection allows for fast and robust identification of loci associated with a desired phenotype. By using a genome-wide marker set to predict phenotypic values, genomic prediction for phenotype-unknown but genotype-determined PIs has become possible. The goal of this study was to describe the genetic architecture associated with sensitivity to Tobacco ringspot virus (TRSV) infection in the USDA Soybean Germplasm Collection. Results TRSV-induced disease sensitivities of the 697 soybean PIs were rated on a one to five scale with plants rated as one exhibiting mild symptoms and plants rated as five displaying terminal bud necrosis (i.e., bud blight). The GWAS identified a single locus on soybean chromosome 2 strongly associated with TRSV sensitivity. Cross-validation showed a correlation of 0.55 (P < 0.01) to TRSV sensitivity without including the most significant SNP marker from the GWAS as a covariate, which was a better estimation compared to the mean separation by using significant SNPs. The genomic estimated breeding values for the remaining 18,955 unscreened soybean PIs in the USDA Soybean Germplasm Collection were obtained using the GAPIT R package. To evaluate the prediction accuracy, an additional 55 soybean accessions were evaluated for sensitivity to TRSV, which resulted in a correlation of 0.67 (P < 0.01) between actual and predicted severities. Conclusion A single locus responsible for TRSV sensitivity in soybean was identified on chromosome 2. Two leucine-rich repeat receptor-like kinase genes were located near the locus and may control sensitivity of soybean to TRSV infection. Furthermore, a comprehensive genomic prediction for TRSV sensitivity for all accessions in the USDA Soybean Germplasm Collection was completed.
  
  
  
• 2016: Marzano, S., Nelson, B., Olutoyosi, A., Bradley, C. A., Hughes, T., Hartman, G. L., Eastburn, D. M., and Domier, L. L. 2016. Identification of diverse mycoviruses through metatranscriptomics characterization of the viromes of five major fungal plant pathogens. Archives of Virology 90(15):6846-63. [link] [view abstract]
  Mycoviruses can have a marked effect on natural fungal communities and influence plant health and productivity. However, a comprehensive picture of mycoviral diversity is still lacking. To characterize the viromes of five widely dispersed plant-pathogenic fungi, Colletotrichum truncatum, Macrophomina phaseolina, Diaporthe longicolla, Rhizoctonia solani, and Sclerotinia sclerotiorum, a high-throughput sequencing-based metatranscriptomic approach was used to detect viral sequences.
  
  
  
• 2016: Harbach, C., Allen, T. W., Bowen, C. R., Davis, J. A., Hill, C. B., Leitman, M., Mueller, D., Padgett, G. B., Phillips, X., Schneider, R., Sikora, E., Singh, A., and Hartman, G. L. 2016. Delayed senescence in soybean: Terminology, research update, and survey results from growers. Plant Health Progress 17:76-83. [download] [view abstract]
  The terms used to describe symptoms of delayed senescence in soybean often are used inconsistently or interchangeably and do not adequately distinguish the observed symptoms in the field. Various causes have been proposed to explain the development of delayed senescence symptoms. In this article, we review published reports on delayed senescence symptoms in soybean, summarize current research findings, provide examples of terms related to specific symptoms, and present an overview of the results of a multi-state survey directed to soybean growers to understand their concerns about delayed soybean senescence. Some of these terms, such as green bean syndrome and green stem syndrome, describe symptoms induced by biotic factors, while other terms describe symptoms associated with abiotic factors. Some delayed senescence terms involve the whole plant remaining green while other terms include just the stem and other plant parts such as pods. In the grower survey, 77% reported observing soybean plants or plant parts that remained green after most plants in the field were fully mature with ripe seed. Most respondents attributed these symptoms to changes in breeding and choice of cultivars. At the end of this article, we standardized the terms used to describe delayed senescence in soybean.
  
  
  
• 2015: Xiang, Y., Scandiani, M. M., Herman, T. K., and Hartman, G. L. 2015. Optimizing conditions of a cell-free toxic filtrate stem cutting assay to evaluate soybean genotype responses to Fusarium species that cause sudden death syndrome. Plant Disease 99:502-507. [link] [view abstract]
  Cell-free toxic culture filtrates from Fusarium virguliforme, the causal fungus of soybean sudden death syndrome (SDS), cause foliar symptoms on soybean stem cuttings similar to those obtained from root inoculations in whole plants and those observed in production fields. The objectives of this study were to (i) optimize the production conditions for F. virguliforme cell-free toxic culture filtrates and the incubation conditions of the stem cutting assay used to test the toxicity of the cell-free toxic culture filtrates, and (ii) use the optimized assay and a whole plant root inoculation assay to compare four SDS-causing isolates on a panel of selected soybean genotypes. Area under the disease progress curve (AUDPC) values were highest (P = 0.05) when cuttings were immersed in culture filtrate of fungus grown in soybean dextrose broth, in filtrate produced from the fungus grown for 18 or 22 days, and when stem cuttings were incubated at 30°C. AUDPC values and shoot dry weights from the whole plant root inoculations and the AUDPC values from the stem cutting assay differed (P < 0.05) among nine soybean genotypes tested with F. virguliforme and F. tucumaniae isolates, and the AUDPC values from the two assays were positively correlated (r = 0.44 at P < 0.0001).
  
  
  
• 2015: Weems, J., Haudenshield, J. S., Bond, J., Hartman, G., Ames, K., and Bradley, C. A. 2015. Effect of fungicide seed treatments on Fusarium virguliforme infection of soybean and development of sudden death syndrome. Canadian Journal of Plant Pathology 37:435-447. [link] [view abstract]
  Sudden death syndrome (SDS), caused by Fusarium virguliforme (Fv), is a major yield-limiting disease of soybean in North America. Infection of soybean seedling roots by Fv results in severe root damage; therefore, fungicide seed treatments could potentially reduce these early-season infections and reduce severity of foliar symptoms that typically occur later in the season. Multiple fungicide seed treatment combinations were evaluated for their effects on Fv infection, DNA concentrations in roots, soybean root development, and SDS development in the field, greenhouse and laboratory trials. Several seed treatments decreased root disease symptoms compared with the non-treated inoculated control in the laboratory assay, and the biological seed treatment, Bacillus pumilus, significantly decreased seedling development and increased SDS root disease compared with the non-treated inoculated control. In the greenhouse, Fv DNA concentrations in roots were reduced by a treatment combining mefenoxam + thiophanate-methyl + azoxystrobin + Bacillus pumilus + prothioconazole + fludioxonil compared with the non-treated control; however, the reduction in Fv DNA did not improve root growth or decrease SDS symptoms compared with the non-treated control. Field trials were conducted in Valmeyer, IL in 2008 and in Urbana, IL in 2008 and 2009. Seed treatments had no effect on the concentration of Fv DNA in soybean roots and had very little effect on root morphology. At the Valmeyer location, most seed treatments significantly decreased SDS symptoms compared with the control. In summary, no consistent, significant effects of the seed treatments evaluated in this study on SDS or Fv root infection were observed. Therefore, soybean growers should continue to utilize other practices for SDS management until new seed treatments with consistent efficacy in controlling SDS are available.
  
  
  
• 2015: Murithi, H. H., Beed, F., Soko, M., Haudenshield, J. S., and Hartman, G. L. 2015. First Report of Phakopsora pachyrhizi on soybean causing rust in Malawi. Plant Disease 99:420. [link] [view abstract]
  Soybean rust (SBR), caused by Phakopsora pachyrhizi, has become established in Africa since the first report in Uganda in 1996 (2). The urediniospores, as windborne propagules, have infested new regions of Africa, initiating SBR in many countries, including Ghana and Democratic Republic of the Congo in 2007 (4) and Tanzania in 2014 (3). No refereed reports have been published about rust in Malawi, but some people have indicated that soybean rust may have been observed as early as 2008. Typical symptoms and signs of SBR, including leaf yellowing and tan, sporulating uredinia, were observed on soybean in May 2014 during field surveys in the major soybean-growing areas of Malawi, including the central (Dowa, Mchinji, and Kasungu) and southern (Thyolo) regions in nine out of 12 sites surveyed. When microscopically examined, urediniospores were elliptical, echinulate, and hyaline to pale yellowish brown. Leaves exhibiting sporuliferous uredinia were sent by APHIS permit to the University of Illinois. To confirm the pathogen, symptomatic soybean leaf tissue of approximately 1 cm2 was excised from each of the samples, and DNA was extracted using the FastDNA Spin Kit (MP Biomedicals, Solon, OH), with further purification using the MicroElute DNA Clean-up Kit (Omega Bio-Tek, Norcross, GA). The resulting DNA was analyzed by quantitative PCR using published Taqman assays for P. pachyrhizi and P. meibomiae, with a multiplexed exogenous internal control reaction to validate negative results (1). P. pachyrhizi DNA was detected in excess of 180,000 genome equivalents/cm2 in all samples, indicating a substantial infection. P. meibomiae DNA was determined to be absent from all samples, within the limit of quantification of ~2 pg DNA/cm2. Urediniospores dislodged from three leaves and inoculated onto susceptible soybean cultivar Williams 82 produced tan lesions after 2 weeks of incubation in a detached-leaf assay. This is the first confirmed report of P. pachyrhizi causing rust on soybean in Malawi, putting at risk 14,000 ha currently under soybean production. The reports of soybean rust in Malawi and adjoining countries will alter soybean production practices and research interests. In some cases, foliar application of fungicides has increased and planting dates have been changed to avoid conditions that are most conducive for rust development. Efforts to understand the virulence and genetic diversity of the pathogen in the region are needed in order to develop and deploy resistant cultivars.
  
  
  
• 2015: Hartman, G. L., Chang, H.-X., and Leandro, L. F. 2015. Research advances and management of soybean sudden death syndrome. Crop Protection 73:60-66. [link] [view abstract]
  Fusarium virguliforme causes soybean sudden death syndrome (SDS) in the United States. The disease was first observed in Arkansas in 1971, and since has been reported in most soybean-producing states, with a general movement from the southern to the northern states. In addition to F. virguliforme, three other species, Fusarium brasiliense, Fusarium crassistipitatum, and Fusarium tucumaniae, have been reported to cause SDS in South America. Yield losses caused by F. virguliforme range from slight to 100%. Severely infected plants often have increased flower and pod abortion, reduced seed size, increased defoliation, and prematurely senescence. Foliar symptoms observed in the field are most noticeable from mid to late reproductive growth stages. To manage SDS, research on crop rotations, soil types, tillage practices, seed treatments, and the development and utilization of host resistance has been investigated. This review focuses on what is known about F. virguliforme, the management of SDS in the United States, and how genetic engineering along with other traditional management options may be needed as integrated approaches to manage SDS.
  
  
  
• 2015: Marzano, S., Hobbs, H. A., Nelson, R. L., Hartman, G. L., Eastburn, D. M., McCoppin, N. K., and Domier, L. L. 2015. Transfection of Sclerotinia sclerotiorum with in vitro transcripts of a naturally occurring interspecific recombinant of Sclerotinia sclerotiorum hypovirus 2 significantly reduces virulence of the fungus. Journal of Virology 89:5060-5071. [link] [view abstract]
  A recombinant strain of Sclerotinia sclerotiorum hypovirus 2 (SsHV2) was identified from a North American Sclerotinia sclerotiorum isolate (328) from lettuce (Lactuca sativa L.) by high-throughput sequencing of total RNA. The 5'- and 3'-terminal regions of the genome were determined by rapid amplification of cDNA ends. The assembled nucleotide sequence was up to 92% identical to two recently reported SsHV2 strains but contained a deletion near its 5' terminus of more than 1.2 kb relative to the other SsHV2 strains and an insertion of 524 nucleotides (nt) that was distantly related to Valsa ceratosperma hypovirus 1. This suggests that the new isolate is a heterologous recombinant of SsHV2 with a yet-uncharacterized hypovirus. We named the new strain Sclerotinia sclerotiorum hypovirus 2 Lactuca (SsHV2L) and deposited the sequence in GenBank with accession number KF898354. Sclerotinia sclerotiorum isolate 328 was coinfected with a strain of Sclerotinia sclerotiorum endornavirus 1 and was debilitated compared to cultures of the same isolate that had been cured of virus infection by cycloheximide treatment and hyphal tipping. To determine whether SsHV2L alone could induce hypovirulence in S. sclerotiorum, a full-length cDNA of the 14,538-nt viral genome was cloned. Transcripts corresponding to the viral RNA were synthesized in vitro and transfected into a virus-free isolate of S. sclerotiorum, DK3. Isolate DK3 transfected with SsHV2L was hypovirulent on soybean and lettuce and exhibited delayed maturation of sclerotia relative to virus-free DK3, completing Koch's postulates for the association of hypovirulence with SsHV2L.
  
  
  
• 2015: Helfenstein, J., Pawlowski, M., Hill, C. B., Stewart, J. M., Lagos-Kutz, D., Bowen, C., Frossard, E., and Hartman, G. 2015. Zinc deficiency alters soybean susceptibility to pathogens and pests. J. Plant Nutr. Soil Sci. 178:896-903. [link] [view abstract]
  Inadequate plant nutrition and biotic stress are key threats to current and future crop yields. Zinc (Zn) deficiency and toxicity in major crop plants have been documented, but there is limited information on how pathogen and pest damage may be affected by differing plant Zn levels. In our study, we used soybean plants as a host, a soybean pest, and three soybean pathogens to determine whether plant Zn levels change pest and disease assessments. Two soybean cultivars were grown in sand culture with a soluble nutrient solution that ranged from Zn-deficient to toxic. Detached leaves from these plants were either inoculated with Aphis glycines, the soybean aphid, Xanthomonas axonopodis pv. glycines, a bacterium that causes bacterial pustule, Sclerotinia sclerotiorum, the necrotrophic fungus responsible for stem rot, or Phakopsora pachyrhizi, a biotrophic obligate pathogen that causes soybean rust. There were significant (P < 5%) effects on aphid colonization, positive counts for bacterial pustule, S. sclerotiorum leaf area affected, and numbers of rust lesions associated with the Zn treatments. Plants grown with the physiologically optimal levels of Zn (2 µM) had less (P < 5%) soybean aphids cm−2 leaflet than plants grown without Zn, at 0.1× Zn (0.2 µM), or at 100× Zn fertilization (200 µM). Plants grown with the normal fertilization of Zn or 100× Zn had fewer (P < 5%) positive counts for bacterial pustule and less lesion area affected by S. sclerotiorum than plants grown without Zn or fertilized with 0.1× Zn. For soybean rust, plants grown with the physiologically optimal fertilization of Zn or 100× Zn had higher (P < 5%) lesions cm−2 on leaflets from plants grown without Zn or fertilized with 0.1× Zn. These results indicate different Zn nutrition levels in soybean significantly affected aphid and disease development.
  
  
  
• 2015: Hartman, G. L., Bowen, C. R., Haudenshield, J. S., Fox, C., Cary, T. R., and Diers, B. W. 2015. Evaluation of disease and pest damage on soybean cultivars released from 1923 through 2008 under field conditions in Central Illinois. Agronomy Journal 107:2373-2380. [link] [view abstract]
  Diseases and pests of soybean [Glycine max (L.) Merr.] often reduce soybean yields. Targeted breeding that incorporates known genes for resistance and non-targeted breeding that eliminates susceptible plants in breeding populations reduces the impact of soybean pathogens and pests. Maturity group (MG) III soybean cultivars released from 1923 through 2008 were grown in three field environments to determine if disease and insect ratings were associated with year of cultivar release. Disease and pest ratings were evaluated on 40 soybean cultivars at one location (Urbana, IL) planted in two rotation treatments in 2010 and on 59 cultivars in two locations (Urbana and Arthur) in 2011. During the season, foliar disease symptoms and insect foliar feeding damage were recorded. At harvest maturity, stem diseases were assessed. In at least one environment, foliar incidence reached 100% for bacterial diseases, brown spot (Septoria glycines Hemmi), and insect foliar feeding damage and 100% incidence for anthracnose [Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore], Cercospora stem blight (Cercospora kikuchiiT. Matsumoto & Tomoy.), and charcoal rot [Macrophomina phaseolina (Tassi) Goid.] on stems for all cultivars. For the nine different disease and pest severity assessments in 2010, seven had a significant (P < 0.05) negative correlation to year of cultivar release indicating that cultivars more recently released had lower severity ratings than cultivars with older release dates. This study demonstrated that incidence and severity of diseases were less pronounced on more newly-released soybean cultivars, showing that decades of breeding has resulted in increased disease resistance in modern soybean cultivars.
  
  
  
• 2015: Pawlowski, M., Hill, C. B., and Hartman, G. L. 2015. Resistance to charcoal rot identified in ancestral soybean germplasm. Crop Science 55:1230-1236. [link] [view abstract]
  Charcoal rot, caused by the fungal pathogen Macrophomina phaseolina, is an economically important disease on soybean and other crops including maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and sunflower (Helianthus annuus L.). Without effective cultural or chemical options to control charcoal rot in soybean [Glycine max (L.) Merr.], finding sources of genetic resistance is of high interest. In this study, 70 ancestral soybean genotypes were screened for resistance to M. phaseolina using a cut-stem inoculation technique under semi-controlled greenhouse conditions. Lesion progression on the stems in the first experiment was measured 7 to 15 d after inoculation. Three follow-up experiments were conducted to select and confirm the genotypes with the strongest partial resistance. Two experiments evaluated lesion lengths and the third experiment evaluated seedling survival. In the two experiments measuring lesion lengths, PI 548302 (42 and 38 mm) and PI 548414 (36 and 52 mm) had significantly shorter lesion lengths than the moderately resistant genotype, DT97-4290 (58 and 87 mm). In the fourth experiment, percentage survival of PI 548414 (88%), PI 548302 (81%), and PI 548178 (66%) were significantly higher than survival of DT97-4290 (32%). These three genotypes may be useful as parents for developing soybean cultivars with charcoal rot resistance.
  
  
  
• 2015: Paul, C., Frederick, R. D., Hill, C. B., Hartman, G. L., and Walker, D. R. 2015. Comparison of pathogenic variation among Phakopsora pachyrhizi isolates collected from the United States and international locations, and identification of soybean genotypes resistant to the U.S. isolates. Plant Disease 99:1059-1069. [download] [view abstract]
  A major constraint in breeding for resistance to soybean rust has been the virulence diversity in Phakopsora pachyrhizi populations. In greenhouse experiments, reactions of 18 soybean genotypes to 24 U.S. isolates from 2007 and 2008 and 4 foreign isolates were compared. Reactions of four differentials (Rpp1 to Rpp4) to these U.S. isolates were also compared with reactions to nine foreign isolates and three U.S. isolates from 2004. Principal component analysis (PCA) of the reaction types grouped the U.S. isolates into a single virulence group, whereas each of the foreign isolates had a unique virulence pattern. In another experiment, reactions of 11 differentials to the 24 U.S. isolates were compared and significant interactions (P < 0.001) were found between the isolates and host genotypes for rust severity and uredinia densities. PCA of these two measures of disease placed the 24 isolates into seven or six aggressiveness groups, respectively. In a third experiment, evaluation of 20 soybean genotypes for resistance to the previously established aggressive groups identified 10 genotypes resistant to isolates representing most of the groups. This study confirmed the pathogenic diversity in P. pachyrhizi populations and identified soybean germplasm with resistance to representative U.S. isolates that can be used in breeding.
  
  
  
• 2015: Kelly, H. Y., Dufault, N. S., Walker, D. R., Isard, S. A., Schneider, R. W., Giesler, L. J., Wright, D. L., Marios, J. J., and Hartman, G. L. 2015. From select agent to an established pathogen, the response to Phakopsora pachyrhizi in North America. Phytopathology 105:905-916. [download] [view abstract]
  The pathogen causing soybean rust, Phakopsora pachyrhizi, was first described in Japan in 1902. The disease was important in the Eastern Hemisphere for many decades before the fungus was reported in Hawaii in 1994, which was followed by reports from countries in Africa and South America. In 2004, P. pachyrhizi was confirmed in Louisiana, making it the first report in the continental United States. Based on yield losses from countries in Asia, Africa, and South America, it was clear that this pathogen could have a major economic impact on the yield of 30 million ha of soybean in the United States. The response by agencies within the United States Department of Agriculture, industry, soybean check-off boards, and universities was immediate and complex. The impacts of some of these activities are detailed in this review. The net result has been that the once dreaded disease, which caused substantial losses in other parts of the world, is now better understood and effectively managed in the United States. The disease continues to be monitored yearly for changes in spatial and temporal distribution so that soybean growers can continue to benefit by knowing where soybean rust is occurring during the growing season.
  
  
  
• 2015: Haudenshield, J. S., and Hartman, G. L. 2015. Archaeophytopathology of Phakopsora pachyrhizi, the soybean rust pathogen. Plant Disease 99:575-579. [download] [view abstract]
  Herbarium specimens are useful to compare attributes of the past to attributes of today and predictions into the future. In this study, herbarium specimens from 1887 to 2006 were used to identify Phakopsora pachyrhizi and P. meibomiae, the two known fungal species that cause soybean rust. Historically, these two species differed in geographic distribution, with P. pachyrhizi confined to Asia and Australia, and P. meibomiae confined to the Americas. In our analyses, herbarium specimens were used to determine whether it was possible to extract adequate useful DNA from the fungal structures. If present, quantitative PCR primers specific to P. pachyrhizi, P. meibomiae, or to a third group inclusive of many rust species could be used to speciate the fungus. Of the 38 archival specimens, 11 were positive for P. pachyrhizi, including a 1912 specimen from Japan; 15 were positive for P. meibomiae, including a 1928 specimen from Brazil and two 1923 specimens from the Philippines; and 12 (including all African accessions) were negative for both species. Five specimens were positive in the more inclusive rust assay; all had been labeled as P. pachyrhizi and none were on soybean. These results demonstrate the feasibility of DNA genotyping in archaeophytopathological investigations.
  
  
  
• 2015: Yang, H.-C., Haudenshield, J. S., and Hartman, G. L. 2015. Multiplex real-time PCR detection and differentiation of Colletotrichum species infecting soybean. Plant Disease 99:1559-1568. [download] [view abstract]
  Colletotrichum species are fungal plant pathogens of worldwide significance. Colletotrichum species were isolated from soybean with anthracnose symptoms in five states in the United States from 2009 to 2013. Among 240 isolates collected, four Colletotrichum species were initially identified by morphological and sequence analysis, including C. chlorophyti, C. incanum, C. truncatum, and Colletotrichum sp. (henceforth Glomerella glycines, the name of its sexual state). To increase diagnostic efficiency and accuracy, real-time multiplex PCR assays based on a double-stranded DNA-binding dye coupled with dissociation curve analysis were designed, using a region of the cytochrome c oxidase subunit 1 (cox1) gene to discern these four Colletotrichum species. Two sets of duplex, real-time PCR assays were established and species differentiation was based upon amplicon melting point temperatures (Tm) in the dissociation curve analysis. The Set 1 duplex assay distinguished C. chlorophyti and G. glycines, and the Set 2 duplex assay distinguished C. incanum and C. truncatum. Successful detection was achieved with as little as 1 pg DNA. The assays were especially useful for differentiating C. chlorophyti, C. incanum, and C. truncatum, which have similar morphological features. Colletotrichum gloeosporioides, another pathogen associated with soybean anthracnose, was not resolved from G. glycines by the melting curve analysis. The two duplex real-time PCR assays were used to screen more than 200 purified Colletotrichum isolates, showing that they were rapid and effective methods to detect and differentiate Colletotrichum species infecting soybean.
  
  
  
• 2015: Kandal, Y. R., Haudenshield, J. S., Srour, A. Y., Islam, K. T., Fakhoury, A. M., Chilvers, M. I., Wang, J., Santos, P., Hartman, G. L., Malvick, D. K., Floyd, C. M., Mueller, D. S., and Leandro, L. F. S. 2015. Multi-laboratory comparison of quantitative PCR assays for detection and quantification of Fusarium virguliforme from soybean roots and soil. Phytopathology 105:1601-1611. [download] [view abstract]
  The ability to accurately detect and quantify Fusarium virguliforme, the cause of sudden death syndrome (SDS) in soybean, in samples such as plant root tissue and soil is extremely valuable for accurate disease diagnoses and to address research questions. Numerous quantitative real-time polymerase chain reaction (qPCR) assays have been developed for this pathogen but their sensitivity and specificity for F. virguliforme have not been compared. In this study, six qPCR assays were compared in five independent laboratories using the same set of DNA samples from fungi, plants, and soil. Multicopy gene-based assays targeting the ribosomal DNA intergenic spacer (IGS) or the mitochondrial small subunit (mtSSU) showed relatively high sensitivity (limit of detection [LOD] = 0.05 to 5 pg) compared with a single-copy gene (FvTox1)-based assay (LOD = 5 to 50 pg). Specificity varied greatly among assays, with the FvTox1 assay ranking the highest (100%) and two IGS assays being slightly less specific (95 to 96%). Another IGS assay targeting four SDS-causing fusaria showed lower specificity (70%), while the two mtSSU assays were lowest (41 and 47%). An IGS-based assay showed consistently highest sensitivity (LOD = 0.05 pg) and specificity and inclusivity above 94% and, thus, is suggested as the most useful qPCR assay for F. virguliforme diagnosis and quantification. However, specificity was also above 94% in two other assays and their selection for diagnostics and research will depend on objectives, samples, and materials used. These results will facilitate both fundamental and disease management research pertinent to SDS.
  
  
  
• 2015: Yang, H.-C., and Hartman, G. L. 2015. Methods and evaluation of soybean genotypes for resistance to Colletotrichum truncatum. Plant Disease 99:143-148. [download] [view abstract]
  Anthracnose of soybean (Glycine max) occurs throughout the soybean production areas of the world. There is little information on evaluating inoculation techniques or evaluating soybean germplasm for resistance. The objectives of this study were to develop a reliable inoculation technique for evaluating soybean for resistance to Colletotrichum truncatum and to evaluate soybean genotypes for resistance. Inoculated plants incubated in a dew chamber for 48 or 72 h had higher (P = 0.05) area under disease progress curve (AUDPC) values than when incubated for 24 h. Three experiments evaluated soybean genotypes for resistance to C. truncatum. In the first experiment using 15 soybean genotypes, ‘Mandarin’ had lower (P = 0.05) AUDPC values than all the other genotypes except for ‘Mandarin 507’, ‘Mandarin (Ottawa)’, and ‘Boone’. In the second experiment using 28 soybean genotypes, Mandarin 507 had lower (P = 0.05) AUDPC values compared with all other soybean genotypes except ‘Early White Eyebrow’, ‘Mandarin Yowa’, Boone, and ‘Manchuria’. In the third experiment, Mandarin 507 had lower (P = 0.05) AUDPC values compared with 23 other soybean genotypes except ‘Spry’, Mandarin, and ‘Iroquois’. Plants of Mandarin 507 and ‘Williams 82’ were inoculated at the vegetative and reproductive growth stages; Mandarin 507 had lower (P = 0.05) AUDPC values compared with Williams 82 for both growth stages evaluated, and Mandarin 507 had less (P = 0.05) pod area covered by lesions compared with the pods of Williams 82. This study provided a descriptive method to inoculate soybean plants with C. truncatum and identified soybean genotypes with resistance to anthracnose.
  
  
  
• 2014: Zernova, O. V., Lygin, A. V., Pawlowski, M. L., Hill, C. B., Hartman, G. L., Widholm, J. M., Lozovaya, V. V. 2014. Regulation of plant immunity through modulation of phytoalexin synthesis. Molecules 19: 7480-7496. doi:10.3390/molecules19067480. [link] [view abstract]
  Soybean hairy roots transformed with the resveratrol synthase and resveratrol oxymethyl transferase genes driven by constitutive Arabidopsis actin and CsVMV promoters were characterized. Transformed hairy roots accumulated glycoside conjugates of the stilbenic compound resveratrol and the related compound pterostilbene, which are normally not synthesized by soybean plants. Expression of the non-native stilbenic phytoalexin synthesis in soybean hairy roots increased their resistance to the soybean pathogen Rhizoctonia solani. The expression of the AhRS3 gene resulted in 20% to 50% decreased root necrosis compared to that of untransformed hairy roots. The expression of two genes, the AhRS3 and ROMT, required for pterostilbene synthesis in soybean, resulted in significantly lower root necrosis (ranging from 0% to 7%) in transgenic roots than in untransformed hairy roots that had about 84% necrosis. Overexpression of the soybean prenyltransferase (dimethylallyltransferase) G4DT gene in soybean hairy roots increased.
  
  
  
• 2014: Chang, S., Thurber, C. S., Brown, P. J., Hartman, G. L., Lambert K. N., et al. 2014. Comparative mapping of the wild perennial Glycine latifolia and soybean (G. max) reveals extensive chromosome rearrangements in the genus Glycine. PLoS ONE 9(6): e99427. [link] [view abstract]
  Soybean (Glycine max L. Mer.), like many cultivated crops, has a relatively narrow genetic base and lacks diversity for some economically important traits. Glycine latifolia (Benth.) Newell & Hymowitz, one of the 26 perennial wild Glycine species related to soybean in the subgenus Glycine Willd., shows high levels of resistance to multiple soybean pathogens and pests including Alfalfa mosaic virus, Heterodera glycines Ichinohe and Sclerotinia sclerotiorum (Lib.) de Bary. However, limited information is available on the genomes of these perennial Glycine species. To generate molecular resources for gene mapping and identification, high-density linkage maps were constructed for G. latifolia using single nucleotide polymorphism (SNP) markers generated by genotyping by sequencing and evaluated in an F2 population and confirmed in an F5 population. In each population, greater than 2,300 SNP markers were selected for analysis and segregated to form 20 large linkage groups. Marker orders were similar in the F2 and F5 populations. The relationships between G. latifolia linkage groups and G. max and common bean (Phaseolus vulgaris L.) chromosomes were examined by aligning SNP containing sequences from G. latifolia to the genome sequences of G. max and P. vulgaris. Twelve of the 20 G. latifolia linkage groups were nearly collinear with G. max chromosomes. The remaining eight G. latifolia linkage groups appeared to be products of multiple interchromosomal translocations relative to G. max. Large syntenic blocks also were observed between G. latifolia and P. vulgaris. These experiments are the first to compare genome organizations among annual and perennial Glycine species and common bean. The development of molecular resources for species closely related to G. max provides information into the evolution of genomes within the genus Glycine and tools to identify genes within perennial wild relatives of cultivated soybean that could be beneficial to soybean production.
  
  
  
• 2014: Pawlowski, M., Hill, C. B., Hartman, G. L and Voegtlin D.J. 2014. Soybean aphid intrabiotype variability based on colonization of specific soybean genotypes. Insect Science 00, 1–8, DOI 10.1111/1744-7917.12169 [link] [view abstract]
  The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the most destructive insect pests on soybeans in the United States. One method for managing this pest is through host plant resistance. Since its arrival in 2000, 4 aphid biotypes have been identified that are able to overcome soybean aphid resistance (Rag) genes. A soybean aphid isolate collected from Moline, Illinois readily colonized soybean plants with the soybean aphid resistance gene Rag2, unlike biotypes 1 and 2, but similar to soybean aphid biotype 3. Two no-choice experiments compared the virulence of the Moline isolate with biotype 3. In both experiments, differences in aphid population counts were not significant (P>0.05) on soybean genotypes LD08–12957a (Rag2) and LD11–5413a (Rag2), but the aphid counts for the Moline isolate were significantly (P<0.05) lower than the aphid counts for the biotype 3 isolate on the soybean genotypes Dowling (Rag1), LD05–16611 (Rag1), LD11–4576a (Rag1), and PI 567598B (rag1b and rag3). The Moline isolate was a variant of aphid biotype 3, which is the first report showing that soybean aphid isolates classified as the same biotype, based on virulence against specific Rag genes, can differ in aggressiveness or ability to colonize specific host genotypes.
  
  
  
• 2014: Kim, K.-S., Chirumamilla, A., Hill, C.B., Hartman, G.L. and Diers, B.W. 2014. Identification and molecular mapping of two soybean aphid resistance genes in soybean PI 587732. Theor Appl Genet 127:1251–1259. DOI 10.1007/s00122-014-2296-9. [link] [view abstract]
  Soybean [Glycine max (L.) Merr.] continues to be plagued by the soybean aphid (Aphis glycines Matsumura: SA) in North America. New soybean resistance sources are needed to combat the four identified SA biotypes. The objectives of this study were to determine the inheritance of SA resistance in PI 587732 and to map resistance gene(s). For this study, 323 F2 and 214 F3 plants developed from crossing PI 587732 to two susceptible genotypes were challenged with three SA biotypes and evaluated with genetic markers. Choice tests showed that resistance to SA Biotype 1 in the first F2 population was controlled by a gene in the Rag1 region on chromosome 7, while resistance to SA Biotype 2 in the second population was controlled by a gene in the Rag2 region on chromosome 13. When 134 F3 plants segregating in both the Rag1 and Rag 2 regions were tested with a 1:1 mixture of SA Biotypes 1 and 2, the Rag2 region and an interaction between the Rag1 and Rag2 regions were significantly associated with the resistance. Based on the results of the non-choice tests, the resistance gene in the Rag1 region in PI 587732 may be a different allele or gene from Rag1 from Dowling because the PI 587732 gene showed antibiosis type resistance to SA Biotype 2 while Rag1 from Dowling did not. The two SA resistance loci and genetic marker information from this study will be useful in increasing diversity of SA resistance sources and marker-assisted selection for soybean breeding programs.
  
  
  
• 2014: Fox, C.M., Kim, K.-S., Cregan, P.B., Hill, C.B., Hartman, G.L. and Diers, B.W. 2014. Inheritance of soybean aphid resistance in 21 soybean plant introductions . Theor Appl Genet 127:43–50. DOI 10.1007/s00122-013-2199-1. [link] [view abstract]
  The soybean aphid [Aphis glycines Matsumura (Hemiptera: Aphididae)] is one of the most important insect pests of soybean [Glycine max (L.) Merr] in the northern USA and southern Canada, and four resistance loci (Rag1– rag4) have been discovered since the pest was identified in the USA in 2000. The objective of this research was to determine whether resistance expression in recently identi¬fied soybean aphid-resistant plant introductions (PIs) was associated with the four Rag loci using a collection of 21 F2 populations. The F2 populations were phenotyped with soy¬bean aphid biotype 1, which is avirulent on plants having any of the currently identified Rag genes, using choice tests in the greenhouse and were tested with genetic markers linked to the four Rag loci. The phenotyping results indi¬cate that soybean aphid resistance is controlled by a sin-gle dominant gene in 14 PIs, by two genes in three PIs, and four PIs had no clear Mendelian inheritance patterns. Genetic markers flanking Rag2 were significantly associ¬ated with aphid resistance in 20 PIs, the Rag1 region was significantly identified in five PIs, and the Rag3 region was identified in one PI. These results show that single domi¬nant gene action at the Rag2 region may be a major source for aphid resistance in the USDA soybean germplasm collection.
  
  
  
• 2014: Chirumamilla, A., Hill, C.B., and Hartman, G.L. 2014. Stability of soybean aphid resistance in soybean across different temperatures. Crop Science 54: 2557-2563. doi:10.2135/cropsci2014.05.0393. [link] [view abstract]
  The soybean aphid (Aphis glycines Matsumura) is the most important insect pest posing a threat to soybean [Glycine max (L.) Merr.] grain production in the United States. Soybean cultivars with resistance are currently being deployed to aid in management of the pest. Temperature has been reported to influence the expression of host plant resistance against crop pests. The objective of this study was to determine if temperatures, 14, 21, and 28°C, altered resistance expression in four aphid-resistant soybean genotypes, LD05-16611 (with the Rag1 resistance gene), PI 200538 (Rag2), PI 567541B (rag1c, rag4), and PI 567597C (antixenosis) compared to a susceptible soybean genotype (Williams 82) when challenged with soybean aphid. A replicated no-choice experiment was conducted and aphid populations of the three soybean aphid biotypes, 1, 2, and 3, were enumerated 14 d after inoculating the five soybean genotypes. Significant interactions were found in the analysis of the effects of temperature, soybean genotype, and aphid biotype on aphid populations. Responses between soybean genotypes and aphid biotypes were consistent with previous reports with the exception of PI 567541B, which had lower resistance against aphid biotype 1 than found in an earlier study. At 14°C, there was limited aphid population growth on all soybean genotypes, including Williams 82. At 21 and 28°C, resistance expression was stable in LD05-16611 (Rag1), PI 567541B (rag1c, rag4), and PI 567597C (antixenosis), relative to susceptible Williams 82; however, resistance expressed in PI 200538 (Rag2) was significantly stronger at 28°C than at 21°C, as indicated by differences in aphid population size that were found. Results of this study indicated that soybean aphid virulence variability had a stronger influence on the effectiveness of soybean aphid resistance than did temperature, and that the aphid resistance tested in this study would remain stable or be stronger in temperatures ranging between 21 and 28°C.
  
  
  
• 2014: Marvelli, R., Hobbs, H. A., Li, S., McCoppin, N. K., Domier, L. L., Hartman, G. L., and Eastburn, D. M. 2014. Identification of novel double-stranded RNA mycoviruses of Fusarium virguliforme and evidence of their effects on virulence. Archives of Virology 159:349-352. [link] [view abstract]
  Virulence and double-stranded RNA (dsRNA) profiles of 44 isolates of Fusarium virguliforme were compared. When grouped according to dsRNA profiles, isolates with large dsRNAs were significantly (P≤0.05) less virulent than isolates without dsRNAs. High-throughput sequence analysis of total RNA prepared from cultures with large dsRNAs identified two novel RNA viruses with genome sequences of approximately 9.3 kbp, which were named Fusarium virguliforme dsRNA mycovirus 1 and Fusarium virguliforme dsRNA mycovirus 2. The new viruses were most closely related to a group of unclassified viruses that included viruses of F. graminearum and Phlebiopsis gigantic and are related to members of the family Totiviridae.
  
  
  
• 2014: Cui, D., Zhang, Q., Li, M., Slaminko, T. L., and Hartman, G. L. 2014. A method for determining the severity of sudden death syndrome in soybeans. Transactions of the ASABE 57:671-678. [link] [view abstract]
  Sudden death syndrome (SDS), caused by the fungus Fusarium virguliforme, is a widespread mid- to late-season soybean disease with distinctive foliar symptoms that in some extreme cases may cause nearly 100% yield loss. This article reports on the development of an image analysis method to quantify SDS severity using an RGB camera under natural light in a laboratory environment. An HSI (hue, saturation, and intensity) color space based image processing approach was developed. A lesion index (LI) was defined as the ratio of affected leaf area to healthy area for evaluating SDS severity levels on leaves of infected plants. A method of using the frequency distribution of hue values of whole leaf area to measure the severity of SDS was also investigated. Preliminary results obtained from laboratory-scale validation demonstrated that the developed method could provide a feasible means of recording SDS severity in situ that could potentially be used for high-throughput greenhouse evaluation of breeding lines or commercial soybean cultivars.
  
  
  
• 2014: Murithi, H. H., Madata, C. S., Haudenshield, J. S., and Hartman, G. L. 2014. First report of Phakopsora pachyrhizi on soybean causing rust in Tanzania. Plant Disease 98:1586. [link] [view abstract]
  Phakopsora pachyrhizi Syd. was reported on legume hosts other than soybean in Tanzania as early as 1979 (1). Soybean rust (SBR), caused by P. pachyrhizi, was first reported on soybean in Africa in Uganda in 1996 (3), and its introduction into Africa was proposed to occur through urediniospores blowing from western India to the African east coastal areas by moist northeast monsoon winds (4). The fungus rapidly spread and was reported on soybean in South Africa in 2001, in western Cameroon in 2003, and in Ghana and the Democratic Republic of the Congo in 2007 (5). A second species causing SBR on soybean, P. meibomiae, has not been reported in Africa or elsewhere, outside of the Americas. From 2012 to 2014, symptomatic leaf samples were collected in the major soybean growing areas of the Tanzanian Southern Highlands (Iringa, Mbeya, and Ruvuma regions). Symptoms of SBR included yellowing of leaves and tan sporulating lesions. These symptoms were observed at flowering through seed maturity. From fields surveyed in 2012, 2013, and 2014, SBR was observed in 5 of 14, 7 of 11, and 14 of 31 fields, respectively. Some of the leaves sampled had up to 80% of the leaf area affected. When microscopically examined, urediniospores were elliptical, echinulate, and hyaline to pale yellowish brown. In 2014, sporuliferous uredinia were observed on leaf material collected from the Iringa and Ruvuma regions of Tanzania, and a subset of these samples was sent by APHIS permit to the University of Illinois. To confirm the pathogen, symptomatic soybean leaf tissue of approximately 1 cm2 was excised from each of the samples, and DNA was extracted using the FastDNA Spin Kit (MP Biomedicals, Solon, OH), with further purification using the MicroElute DNA Clean-up Kit (Omega Bio-Tek, Norcross, GA). The DNA was subjected to quantitative PCR using published Taqman assays for P. pachyrhizi, P. meibomiae, and a multiplexed exogenous internal control reaction to validate negative results (2). P. pachyrhizi DNA was detected in excess of 66,000 genome equivalents/cm2 in all samples, and P. meibomiae DNA was determined to be absent from all samples (limit of quantification ~2 pg DNA/cm2). Free surviving urediniospores were dislodged from 12 samples and inoculated onto susceptible soybean cultivar Williams 82, which produced sporulating SBR lesions after 2 weeks of incubation in a detached-leaf assay. Thus, Koch's postulates were completed. This is the first report of P. pachyrhizi causing rust on soybean in Tanzania. In vivo cultures have been established from most of these samples, and ongoing research includes an evaluation of the P. pachyrizi virulence on a differential set, and characterization of the genetic diversity.
  
  
  
• 2014: Yang, H.-C., Haudenshield, J. S., and Hartman, G. L. 2014. Colletotrichum incanum sp. nov., a curved-conidial species causing soybean anthracnose in the USA. Mycologia 106:32-42. [link] [view abstract]
  Soybean anthracnose is caused by a number of species of Colletotrichum that as a group represent an important disease that results in significant economic losses. In the current study, Colletotrichum species were isolated from soybean petioles and stems with anthracnose symptoms from soybean fields in Illinois. Multigene sequence phylogenic analysis, combining rDNA internal transcribed spacer, actin, β-tubulin, glyceraldehyde-3-phosphate dehydrogenase and histone H3 gene regions, revealed a group of isolates collected in this study to be distinct from other established Colletotrichum species. This new group was phylogenetically closer to C. liriopes, C. tofieldiae and C. verruculosum than to C. truncatum, another species with curved conidia commonly found on soybean. A representative isolate from this new group was used to examine its morphology, cultural characteristics and pathogenicity to soybean; it was found to differ from C. truncatum in colony culture characteristics and sizes of conidia and appressoria. As a result of the molecular phylogenetic, morphological and pathogenicity analyses, we named this species Colletotrichum incanum. Of the 84 Colletotrichum isolates collected from soybean petioles, 40 were C. incanum, indicating that this species may commonly occur.
  
  
  
• 2014: Chang, H-X, Miller, L. A., Hartman, G. L. 2014. Melanin-independent accumulation of turgor pressure in appressoria of Phakopsora pachyrhizi. Phytopathology 104:977-984. [download] [view abstract]
  Appressoria of some plant pathogenic fungi accumulate turgor pressure that produces a mechanical force enabling the direct penetration of hyphae through the epidermis. Melanin has been reported to function as an impermeable barrier to osmolytes, which allow appressoria to accumulate high turgor pressure. Deficiency of melanin in appressoria has been shown to reduce turgor pressure and compromise the infection process. In Phakopsora pachyrhizi, the soybean rust pathogen, the appressoria are transparent. Our objective was to determine if melanin inhibitors would alter appressorial turgor pressure and if a melanin layer would form specifically between the appressorial cell wall and plasma membrane. We used two melanin biosynthesis inhibitors and found that these melanin inhibitors did not reduce turgor pressure or compromise the infection process. In addition, the turgor pressure of P. pachyrhizi appressoria ranged from 5 to 6 MPa based on extracellular osmolytes used to simulate different osmotic pressures. Transmission electron microscopy also showed the absence of a melanin layer between the appressorial cell wall and plasma membrane. This is the first report showing that turgor pressure accumulation of P. pachyrhizi appressoria was independent of melanin.
  
  
  
• 2014: Lygin, A. V., Hill, C. B., Pawlowski, M., Zernova, O. V., Widholm, J. M., Hartman, G. L., and Lozovaya, V. V. 2014. Inhibitory effects of stilbenes on the growth of three soybean pathogens in culture. Phytopathology 104:843-850. [download] [view abstract]
  The effects of resveratrol and pterostilbene on in vitro growth of three soybean pathogens were tested to determine whether these stilbenic compounds could potentially be targets to increase innate resistance in transgenic soybean plants. Growth of Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum was measured on solid and in liquid media amended with resveratrol and pterostilbene (concentration in the media of resveratrol at 100 μg/ml and pterostilbene at 25 μg/ml). All three fungi were very sensitive to pterostilbene in potato dextrose agar (PDA), which reduced colony area of each of the three pathogens to less than half of the control 3 days after incubation. The three fungal pathogens were less sensitive to resveratrol compared with pterostilbene; however, area under the curve (AUC) calculated from colony areas measured over 3 days was significantly (P < 0.05) less than the control for S. sclerotiorum and R. solani on PDA with resveratrol or pterostilbene. AUC for M. phaseolina on PDA with pterostilbene was significantly (P < 0.05 lower than the control whereas, on PDA with resveratrol, AUC for M. phaseolina was lower than the control but the difference was nonsignificant (P > 0.05). AUC for all three fungi was significantly lower (P < 0.05) on PDA with pterostilbene than with resveratrol. In potato dextrose broth (PDB) shake cultures, AUC for all three fungi was significantly (P < 0.01) lower in pterostilbene than in the control. AUC for R. solani and S. sclerotiorum was significantly lower (P < 0.01) in resveratrol than the control, whereas AUC for M. phaseolina, in resveratrol was lower, but not significantly (P > 0.05) different from the control. AUC in pterostilbene was highly significantly (P < 0.01) lower than in resveratrol for M. phaseolina, and significantly (P < 0.05) lower for R. solani but the difference for S. sclerotiorum was nonsignificant (P > 0.05). There was a trend for lower mass accumulation of all three fungi in either pterostilbene or resveratrol compared with the control during the course of the experiment; however, S. sclerotiorum appeared to recover from the effects of pterostilbene between days 2 and 4. Results of biochemical analyses of the PDB over time indicated that the three fungi degraded resveratrol, with nearly 75% reduction in concentration in M. phaseolina, 80% in S. sclerotiorum , and 60% in R. solani PDB cultures by day 4 of fungal growth. M. phaseolina and S. sclerotiorum were able to resume growth after early inhibition by resveratrol after its concentration was reduced in the cultures through degradation, whereas R. solani was less efficient in resveratrol degradation and was not able to overcome its inhibitory effects on growth. The capacity to degrade pterostilbene was lowest in M. phaseolina compared with S. sclerotiorum and R. solani and the recovery of M. phaseolina, cultures after initial growth inhibition by pterostilbene was minimal. The potential products of resveratrol and pterostilbene degradation by fungi were identified to be dimers and various oxidation products.
  
  
  
• 2014: Vittal, R., Paul, C., Hill, C. B., and Hartman, G. L. 2014. Characterization and quantification of fungal colonization of Phakopsora pachyrhizi in soybean genotypes. Phytopathology 104:86-94. [download] [view abstract]
  Soybean rust, caused by the fungus Phakopsora pachyrhizi, is an economically important disease of soybean with potential to cause severe epidemics resulting in significant yield losses. Host resistance is one of the management tools to control this disease. This study compared soybean genotypes exhibiting immunity, complete and incomplete resistance, and susceptibility to an isolate of P. pachyrhizi based on visual assessment of reaction type, other visual traits such as sporulation, quantitative measurements of the amount of fungal DNA (FDNA) present in leaf tissues, and data on infection and colonization levels. Soybean genotype UG5 (immune), and plant introduction (PI) 567102B and PI 567104B (complete resistance) had lower quantities of uredinia and FDNA than four other genotypes with incomplete resistance. Based on microscopic observations, early events of spore germination, appressorium formation, and fungal penetration of the epidermis occurred within 24 h postinoculation and were similar among the tested soybean genotypes. Differences in infection among the genotypes were evident once the hyphae penetrated into the intercellular spaces between the mesophyll cells. At 2 days after inoculation (dai), soybean genotype Williams 82 had a significantly (P < 0.05) higher percentage of hyphae in the mesophyll tissue than other soybean genotypes, with UG5 having significantly (P < 0.05) lower percentages than all of the other soybean genotypes at 3, 4, and 5 dai. The percentage of interaction sites with mesophyll cell death was significantly (P < 0.05) higher in UG5 than other genotypes at 3, 4, and 5 dai. There was a significant positive correlation (r = 0.30, P < 0.001) between quantities of hyphae in the mesophyll cells and FDNA. These results demonstrated that incompatible soybean–P. pachyrhizi interaction results in restricted hyphal development in mesophyll cell tissue, likely due to hypersensitive apoptosis.
  
  
  
• 2014: Twizeyimana, M., Ojiambo, P. S., Bandyopadhyay, R., and Hartman, G. L. 2014. Use of quantitative traits to assess aggressiveness of Phakopsora pachyrhizi isolates from Nigeria and the United States. Plant Dis. 98:1261-1266. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important foliar diseases of soybean worldwide. The soybean–P. pachyrhizi interaction is often complex due to genetic variability in host and pathogen genotypes. In a compatible reaction, soybean genotypes produce tan-colored lesions, whereas in an incompatible reaction soybean genotypes produce an immune response (complete resistance) or reddish-brown lesions (incomplete resistance). In this study, in total, 116 and 72 isolates of P. pachyrhizi from Nigeria and the United States, respectively, were compared based on six quantitative traits to assess their aggressiveness on two soybean genotypes. All isolates produced reddish-brown lesions on plant introduction (PI) 462312 and tan lesions on TGx 1485-1D. The number of days after inoculation to first appearance of lesions, uredinia, and sporulation, along with the number of lesions and sporulating uredinia per square centimeter of leaf tissue, and the number of uredinia per lesion, were significantly (P < 0.001) different between the two soybean genotypes for all isolates from each country. The number of days to first appearance of lesions, uredinia, and sporulation were greater on PI 462312 than on TGx 1485-1D for all the test isolates. Similarly, the number of lesions and sporulating uredinia per square centimeter, and the number of uredinia per lesion were lower on PI 462312 than on TGx 1485-1D. For both soybean genotypes, the number of sporulating uredinia per square centimeter significantly (P = 0.0001) increased with an increase in the number of lesions per square centimeter. Although the slope of the regression of sporulating uredinia on number of lesions was greater (P < 0.0001) when TGx 1485-1D was inoculated with Nigerian isolates compared with U.S. isolates, slopes of the regression lines did not differ significantly (P > 0.0675) when PI 46312 was inoculated with Nigerian or U.S. isolates. This is the first study that used a large number of isolates from two continents to assess aggressiveness of P. pachyrhizi using multiple traits in soybean genotypes with contrasting types of disease reaction.
  
  
  
• 2014: Xiang, Y., Herman, T.K., Hartman, G.L. 2014. Using soybean milk to culture soybean pathogens. Advances in Microbiology. 4:126-132. [download] [view abstract]
  Liquid and semi-solid culture media are used to maintain and proliferate bacteria, fungi, and Oomycetes for research in microbiology and plant pathology. In this study, a comparison was made between soybean milk medium, also referred to as soymilk, and media traditionally used for culturing soybean pathogens to determine if soymilk medium was an effective medium for growth of Colletotrichum truncatum, Fusarium virguliforme, Macrophomina phaseolina, Passalora sojina, Phomopsis longicolla, Phytophthora sojae, Pythium irregulare, Rhizoctonia solani, and Sclerotinia sclerotiorum. Based on radial mycelial colony growth rates, C. sojina grew significantly (P < 0.05) faster on soymilk dextrose agar (SDA) than on V-8 agar, and C. truncatum and F. virguliforme grew significantly (P < 0.05) faster on SDA than potato dextrose agar (PDA). Significantly (P < 0.001) greater masses of sclerotia were produced by S. sclerotiorum grown on SDA as compared to PDA. Soymilk used with agar or used alone as a broth may be an option for replacing more expensive processed culture media.
  
  
  
• 2014: Sikora, E. J., Allen, T. W., Wise, K. A., Bergstrom, G., Bradley, C. A., Bond, J., Brown-Rytlewski, D., Chilvers, M., Damicone, J., DeWolf, E., Dorrance, A., Dufault, N., Esker, P., Faske, T. R., Giesler, L., Goldberg, N., Golod, J., Gomez, I. R. G., Grau, C., Grybauskas, A., Franc, G., Hammerschmidt, R., Hartman, G. L., Henn, A., Hershman, D., Hollier, C., Isakeit, T., Isard, S., Jacobson, B., Jardine, D., Kemerait, B., Koenning, S., Langham, M., Malvick, D., Markell, S., Marois, J. J., Monfort, S., Mueller, D., Mueller, J., Mulroony, R., Newman, M., Osborne, L., Padgett, G. B., Ruden, B. E., Rupe, J., Schneider, R., Schwartz, H., Shaner, G., Singh, S., Stromberg, E., Sweets, L., Tenuta, A., Vaiciunas, S., Yang, X. B., Young-Kelly, H., and Zidek, J. 2014. A coordinated effort to manage soybean rust in North America: a success story in soybean disease monitoring. Plant Dis. 98:864-875. [download] [view abstract]
  Existing crop monitoring programs determine the incidence and distribution of plant diseases and pathogens and assess the damage caused within a crop production region. These programs have traditionally used observed or predicted disease and pathogen data and environmental information to prescribe management practices that minimize crop loss. Monitoring programs are especially important for crops with broad geographic distribution or for diseases that can cause rapid and great economic losses. Successful monitoring programs have been developed for several plant diseases, including downy mildew of cucurbits, Fusarium head blight of wheat, potato late blight, and rusts of cereal crops. A recent example of a successful disease-monitoring program for an economically important crop is the soybean rust (SBR) monitoring effort within North America. SBR, caused by the fungus Phakopsora pachyrhizi, was first identified in the continental United States in November 2004. SBR causes moderate to severe yield losses globally. The fungus produces foliar lesions on soybean (Glycine max) and other legume hosts. P. pachyrhizi diverts nutrients from the host to its own growth and reproduction. The lesions also reduce photosynthetic area. Uredinia rupture the host epidermis and diminish stomatal regulation of transpiration to cause tissue desiccation and premature defoliation. Severe soybean yield losses can occur if plants defoliate during the mid-reproductive growth stages. The rapid response to the threat of SBR in North America resulted in an unprecedented amount of information dissemination and the development of a real-time, publicly available monitoring and prediction system known as the Soybean Rust-Pest Information Platform for Extension and Education (SBR-PIPE). The objectives of this article are (i) to highlight the successful response effort to SBR in North America, and (ii) to introduce researchers to the quantity and type of data generated by SBR-PIPE. Data from this system may now be used to answer questions about the biology, ecology, and epidemiology of an important pathogen and disease of soybean.
  
  
  
• 2013: Yang, H. -C., Stewart, J. M., Hartman, G. L. 2013. First report of Colletotrichum chlorophyti infecting soybean seed in Arkansas, United States. Plant Disease 97:1510. [link] [view abstract]
  Colletotrichum chlorophyti was first reported in the United States in 2009 on soybean petioles (Glycine max [L.] Merr.) collected from Alabama, Illinois, and Mississippi (4). This species has not been reported to infect seed, unlike other Colletotrichum spp. (2). From the 2012 growing season, soybean seeds obtained from the National Agricultural Statistics Service representing 151 seed lots from growers' fields in 11 states were assayed by plating them on acidified potato dextrose agar (APDA). Before plating, seeds were surface disinfected by sequential immersion in 50% ethanol for 30 s, 20% commercial bleach for 1 min, two 1 min rinses in sterile distilled water, and kept at 25°C in the dark for 1 week. Infected seeds from one seed lot from Arkansas produced colonies similar to Colletotrichum spp. This seed lot was visually examined and divided into asymptomatic or discolored symptomatic seeds. Because of the limited number of seeds in the seed lot, 20 seeds that asymptomatic and 40 seeds that appeared symptomatic were assayed on APDA as previously described. Asymptomatic seeds did not produce any dark fungal colonies. Among the symptomatic seeds, five appeared to have flecked light gray seed coats with some larger grayish to black and irregular spots where cracks were sometimes formed, and they developed small black fungal masses or became entirely dark on the surface. Five fungal isolates were obtained from these infected seeds. On APDA, the isolates initially produced white to pink smooth-margined colonies, turned black with age, produced no aerial growth, and filled a 9 cm diameter petri dish within 10 days. DNA of one isolate was extracted for PCR and sequencing of the ITS region with ITS1 and ITS4 primers (3). From the BLAST analysis, the sequence was 100% identical to C. chlorophyti isolates, IMI 103806, and CBS 142.79 (Accession Nos. GU227894 and GU227895, respectively). To test for pathogenicity, the fungus was sub-cultured on APDA and eight APDA discs (4 mm diameter) were set into 50 ml potato dextrose broth inside a 250-ml flask and shook at a speed of 100 rpm at room temperature (24 ± 1°C) for 10 days. The mycelium was then weighed, fragmented with a blender, and resuspended in sterile distilled water to a final concentration of ~40 mg/ml. The mycelial suspension was sprayed on soybean seedlings of cv. Williams 82 (two plants/pot) at growth stage V1 to V2 until runoff. The inoculated plants were kept in a moist chamber (>90% relative humidity) for 48 h at 24 ± 1°C in the dark, and then transferred to normal plant growing conditions. At 5 days post-inoculation (dpi), the leaves showed typical symptoms caused by C. chlorophyti, including necrosis on the edge of young leaves and petioles, formation of irregular dark brown lesions, and leaves became scrolled (4). Setose acervuli, curved conidia with tapered ends (21.4 ± 1.1 × 3.8 ± 0.3 μm), and chlamydospores were found on the detached symptomatic leaves after 12 dpi. No perithecia formed. The morphology matched the description of C. chlorophyti (1,4). To our knowledge, this is the first report of C. chlorophyti in Arkansas and the first time that this species has been reported infecting seed of any plant.
  
  
  
• 2013: Hill, C. B., Bowen, C. R., and Hartman, G. L. 2013. Effect of fungicide application and cultivar on soybean green stem disorder. Plant Dis. 97:1212-1220. [download] [view abstract]
  Green stem disorder of soybean (Glycine max) has increasingly become a nuisance for soybean producers. The disorder is distinguished from other manifestations of delayed plant maturity by the delayed senescence of stems only, with normal pod ripening and seed maturation.The primary objective of the first study was to determine whether green stem disorder increased with a fungicide treatment. Field cages to isolate soybean plants to prevent insect interactions were used and treatments included maturity group (MG) II insensitive and sensitive soybean cultivars with or without fungicide applications. A secondary objective was to determine fungi potentially associated with the disorder. The results indicated significant elevation of the incidence of green stem disorder when using a fungicide. Species of Diaporthe or Phomopsis and Macrophomina phaseolina were more frequent in stems without the disorder, whereas species of Colletotrichum were found mostly in stems with the disorder. In another study, field experiments were conducted without cages in replicated field plots to compare the effects of fungicides with different chemistries and timing of fungicide application on incidence of green stem disorder using green stem disorder MG II- and MG III-sensitive and insensitive soybean cultivars. There was a significant increase in percentage of green stem disorder due to fungicide application, depending on fungicide chemistry, timing of application, year, location, and cultivar sensitivity to green stem disorder. Generally, Headline and Headline-Domark applications resulted in higher incidence of green stem disorder than Domark alone or the nonsprayed control, with over 50% incidence in many cases. Higher percent green stem disorder was significantly (P < 0.05) associated with higher yields in 11 of the 28 trials. From the results of this research, soybean producers should be aware of the possible risk that fungicide application may have in increasing incidence of green stem disorder. In addition, producers can help manage green stem disorder by selecting soybean cultivars reported to be consistently insensitive to the disorder.
  
  
  
• 2013: Chawla, S. C., Bowen, C. R., Slaminko, T. L., Hobbs, H. A., and Hartman, G. L. 2013. A public program to evaluate commercial soybean cultivars for pathogen and pest resistance. Plant Dis. 97:568-578. [download]
  
  
• 2013: Lygin, A. V., Zernova, O. V., Hill, C. B., Kholina, N. A., Widholm, J. M., Hartman, G. L., and Lozovaya, V. V. 2013. Glyceollin is an important component of soybean plant defense against Phytophthora sojae and Macrophomina. Phytopathology 103:984-994. [download] [view abstract]
  The response of soybean transgenic plants, with suppressed synthesis of isoflavones, and non-transgenic plants to two common soybean pathogens, Macrophomina phaseolina and Phytophthora sojae was studied. Transgenic soybean plants of one line used in this study were previously generated via bombardment of embryogenic cultures with the PAL5 (phenylalanine ammonia lyase), CHS6 (chalcone synthase) and IFS2 (isoflavone synthase) genes in sense orientation, driven by the cotyledon-preferable lectin promoter (to turn genes on in cotyledons), while plants of another line were newly produced using the IFS2 (isoflavone synthase) gene in sense orientation driven by the CsVMV constitutive promoter (to turn genes on in all plant parts). Nearly complete inhibition of isoflavone synthesis was found in the cotyledons of young seedlings of transgenic plants transformed with the IFS2 transgene driven by the cotyledon-preferable lectin promoter compared to the un-transformed control during the 10d observation period, with the precursors of isoflavone synthesis being accumulated in the cotyledons of transgenic plants. These results indicated that the lectin promoter could be active not only during seed development, but also during seed germination. Down regulation of isoflavone synthesis only in the seeds or in the whole soybean plant caused a strong inhibition of the pathogen-inducible glyceollin in cotyledons after inoculation with Phytophthora sojae, which resulted in increased susceptibility of the cotyledons of both transgenic lines to this pathogen compared to inoculated cotyledons of untransformed plants. When stems were inoculated with Macrophomina phaseolina suppression of glyceollin synthesis was found only in stems of transgenic plants expressing transgene driven by constitutive promoter, which developed more severe infection. These results provide further evidence that rapid glyceollin accumulation during infection contributes to the innate soybean defense response.
  
  
  
• 2012: Vittal R., Yang H-C., and Hartman G.L. 2012. Anastomosis of germ tubes and nuclear migration of nuclei in germ tube networks of the soybean rust pathogen, Phakopsora pachyrhizi. European Journal of Plant Pathology 132:163–167. DOI: 10.1007/s10658-011-9872-5. [link] [view abstract]
  An important mechanism for genetic diversity in filamentous fungi is hyphal anastomosis and the formation of heterokaryons. In this study, we observed fusion of germ tubes in germinating urediniospores of Phakopsora pachyrhizi resulting in a complex hyphal network. Staining of the germ tubes derived from P. pachyrhizi urediniospores with 4’, 6-diamidino-2-phenylindole (DAPI) showed migration of nuclei through the network resulting in multinucleate hyphae. Short bridges connecting the hyphal network tubes were also observed. Our study provides the first evidence of germ tube and hyphal anastomosis, and nuclear migration in P. pachyrhizi. Considering the lack of a known sexual stage of P. pachyrhizi, this hyphal anastomosis followed by the parasexual cycle may explain the genetic diversity in virulence among populations of P. pachyrhizi.
  
  
  
• 2012: Kim K.S., Unfried J.R., Hyten D.L., Frederick R.D., Hartman G.L., Nelson R.L., Song Q., Diers B.W. 2012. Molecular mapping of soybean rust resistance in soybean accession PI 561356 and SNP haplotype analysis of the Rpp1 region in diverse germplasm. Theor Appl Genet. 125(6):1339-52. [link] [view abstract]
  Soybean rust (SBR), caused by Phakopsora pachyrhizi Sydow, is one of the most economically important and destructive diseases of soybean [Glycine max (L.) Merr.] and the discovery of novel SBR resistance genes is needed because of virulence diversity in the pathogen. The objectives of this research were to map SBR resistance in plant introduction (PI) 561356 and to identify single nucleotide polymorphism (SNP) haplotypes within the region on soybean chromosome 18 where the SBR resistance gene Rpp1 maps. One-hundred F(2:3) lines derived from a cross between PI 561356 and the susceptible experimental line LD02-4485 were genotyped with genetic markers and phenotyped for resistance to P. pachyrhizi isolate ZM01-1. The segregation ratio of reddish brown versus tan lesion type in the population supported that resistance was controlled by a single dominant gene. The gene was mapped to a 1-cM region on soybean chromosome 18 corresponding to the same interval as Rpp1. A haplotype analysis of diverse germplasm across a 213-kb interval that included Rpp1 revealed 21 distinct haplotypes of which 4 were present among 5 SBR resistance sources that have a resistance gene in the Rpp1 region. Four major North American soybean ancestors belong to the same SNP haplotype as PI 561356 and seven belong to the same haplotype as PI 594538A, the Rpp1-b source. There were no North American soybean ancestors belonging to the SNP haplotypes found in PI 200492, the source of Rpp1, or PI 587886 and PI 587880A, additional sources with SBR resistance mapping to the Rpp1 region.
  
  
  
• 2012: Hill, C.B., Chirumamilla, A. and Hartman, G.L. 2012. Resistance and virulence in the soybean-Aphis glycines interaction. Euphytica 186:635–646. [link] [view abstract]
  Aphis glycines Matsumura, the soybean aphid, first arrived in North America in 2000 and has since become the most important insect pest of domestic soybean, causing significant yield loss and increasing production costs annually in many parts of the USA soybean belt. Research to identify sources of resistance to the pest began shortly after it was found and several sources were quickly identified in the USDA soybean germplasm collection. Characterization of resistance expression and mapping of resistance genes in resistant germplasm accessions resulted in the identification of six named soybean aphid resistance genes: Rag1, rag1c, Rag2, Rag3, rag4, and Rag5 (proposed). Simple sequence repeat markers flanking the resistance genes were identified, facilitating efforts to use marker-assisted selection to develop resistant commercial cultivars. Saturation or fine-mapping with single nucleotide polymorphism markers narrowed the genomic regions containing Rag1 and Rag2 genes. Two potential NBS-LRR candidate genes for Rag1 and one NBS-LRR gene for Rag2 were found within the regions. Years before the release of the first resistant soybean cultivar with Rag1 in 2009, a soybean aphid biotype, named biotype 2, was found that could overcome the resistance gene. Later in 2010, biotype 3 was characterized for its ability to colonize plants with Rag2 and other resistance genes. At present, three biotypes have been reported that can be distinguished by their virulence on Rag1 and Rag2 resistance genes. Frequency and geographic distribution of soybean aphid biotypes are unknown. Research is in progress to determine the inheritance of virulence and develop DNA markers tagging virulence genes to facilitate monitoring of biotypes. With these research findings and the availability of host lines with different resistance genes and biotypes, the soybean aphid-soybean pest-host system has become an important model system for advanced research into the interaction of an aphid with its plant host, and also the tritrophic interaction that includes aphid endosymbionts.
  
  
  
• 2012: Yang, Y.-C., Haudenshield, J. S., and Hartman, G. L. 2012. First report of Colletotrichum chlorophyti causing soybean anthracnose. Plant Dis. 96:1699. [link] [view abstract]
  Anthracnose of soybean [Glycine max (L.) Merr.] is caused by several Colletotrichum spp. (4). Petiole samples were collected from Alabama, Mississippi, and Illinois in 2009. Diseased tissues suspected of being caused by Colletotrichum were cut into 1- to 2-cm lengths, surface-disinfested, and placed on water agar. Pure cultures obtained by picking single spores from sporulating acervuli on tissue or hyphal tips on agar were transferred to acidic potato dextrose agar (APDA) at 24 ±1°C under 12-h cool-white fluorescent lighting. Isolates were grouped by morphological characteristics. One group consisting of six isolates (four from IL and one each from AL and MS) did not morphologically match any reported Colletotrichum spp. causing soybean anthracnose but matched the description of C. chlorophyti S. Chandra & Tandon (1,2). On APDA, colonies were initially pink, turning black after several days with smooth margins and no aerial mycelium. Conidial masses were light salmon in color. Conidia ranged from 15.5 to 21.3 μm long (mean 18.0 μm) × 2.5 to 4.3 wide (mean 3.3 μm) (n = 200). They were curved with tapered ends and a truncated base, aseptate, and hyaline. Chlamydospores were dark brown, clustered or chained together, and 5 to 12 μm wide (n = 30). Setae were straight, dark brown, and septate. Appressoria and perithecia were absent. Soybean plants (cv. Williams 82) at the V2 to V3 stage were atomized with a suspension of fragmented mycelia (40 mg/ml) using one isolate from IL. Plants were kept moist (>90% relative humidity) for 48 h in the dark, then transferred to normal growing conditions. Three days post-inoculation, younger trifoliolate leaf margins and intra- and interveinal lesions were necrotic surrounded by slight chlorosis. Isolations were obtained from symptomatic leaves and confirmed as C. chlorophyti by morphological characteristics. Further comparisons were completed with one isolate (IL1A or BPI 884117) by PCR and BLAST sequencing analyses of the partial ITS rDNA region, actin, β-tubulin, GAPDH, and histone H3 genes (2) (GenBank Accession Nos. JX126475, JX126476, JX126477, JX126478, and JX126479, respectively). The results showed high identity of all the five sequences to two C. chlorophytiisolates, IMI 103806 and CBS 142.79 (Accession Nos. GU227894/GU227895 in ITS = 100%, GU227992/GU227993 in actin = 99%, GU228188/GU228189 in β-tubulin = 99%, GU228286/GU228287 in GAPDH = 99% and 96%, respectively, and GU228090/GU228091 in histone H3 = 99%). Soybean anthracnose, commonly caused by C. truncatum, has curved and truncated conidia that are longer than C. chlorophyti. In addition, the two are distinguished by chlamydospores and lack of appressoria in C. chlorophyti combined with differences in multigene sequence analysis. Isolates of C. chlorophyti were reported to infect Chlorophytum sp. (Liliaceae) in India and Stylosanthes hamate in Australia (3). To our knowledge, there are no previous reports of this species in the United States or of it infecting soybean worldwide (3). This report describes C. chlorophyti as a novel incitant of soybean anthracnose.
  
  
  
• 2012: Vittal, R., Haudenshield, J. S., and Hartman, G. L. 2012. A multiplexed immunofluorescence method identifies Phakopsora pachyrhizi urediniospores and determines their viability. Phytopathology 102:1143-1152. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, occurs concomitantly wherever soybean is grown in the tropical and subtropical regions of the world. After reports of its first occurrence in Brazil in 2001 and the continental United States in 2004, research on the disease and its pathogen has greatly increased. One area of research has focused on capturing urediniospores, primarily by rain collection or wind traps, and detecting them either by microscopic observations or by immunological or molecular techniques. This system of detection has been touted for use as a potential warning system to recommend early applications of fungicides. One shortcoming of the method has been an inability to determine whether the spores are viable. Our study developed a method to detect viable P. pachyrhizi urediniospores using an immunofluorescence assay combined with propidium iodide (PI) staining. Antibodies reacted to P. pachyrhizi and other Phakopsora spp. but did not react with other common soybean pathogens or most other rust fungi tested, based on an indirect immunofluorescence assay using fluorescein isothiocyanate-labeled secondary antibodies. Two vital staining techniques were used to assess viability of P. pachyrhizi urediniospores: one combined carboxy fluorescein diacetate (CFDA) and PI, and the other utilized (2-chloro-4-[2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene]-1-phenylquinolinium iodide] (FUN 1). Using the CFDA-PI method, viable spores stained green with CFDA and nonviable spores counterstained red with PI. Using the FUN 1 method, cylindrical intravacuolar structures were induced to form within metabolically active urediniospores, causing them to fluoresce bright red to reddishorange, whereas dead spores, with no metabolic activity, had an extremely diffused, faint fluorescence. An immunofluorescence technique in combination with PI counterstaining was developed to specifically detect viable P. pachyrhizi urediniospores. The method is rapid and reliable, with a potential for application in forecasting soybean rust based on the detection of viable urediniospores.
  
  
  
• 2012: Twizeyimana, M., Hill, C. B., Pawlowski, M., Paul, C., and Hartman, G. L. 2012. A cut-stem inoculation technique to evaluate soybean for resistance to Macrophomina phaseolina. Plant Dis. 96:1210-1215. [download] [view abstract]
  Charcoal rot of soybean is caused by the fungal pathogen Macrophomina phaseolina. Effective and reliable techniques to evaluate soybean for resistance to this fungus are needed to work toward a management scheme that would utilize host resistance. Three experiments were conducted to investigate the use of a cut-stem inoculation technique to evaluate soybean genotypes for resistance to M. phaseolina. The first experiment compared aggressiveness of M. phaseolina isolates collected from soybean on different soybean genotypes. Significant (P < 0.05) differences among the isolates and genotypes for relative area under disease progress curve (RAUDPC) were found without a significant isolate–genotype interaction. The second experiment compared 14 soybean genotypes inoculated with M. phaseolina in multiple trials conducted in two environments, the greenhouse and growth chamber. Significant (P < 0.05) differences among environments and highly significant (P < 0.001) differences among soybean genotypes for RAUDPC were found. The environment–genotype interaction was nonsignificant (P > 0.05). Soybean genotypes DT97-4290, DT98- 7553, DT98-17554, and DT99-16864 had significantly (P < 0.05) lower RAUDPC than 7 of the 14 genotypes. The third experiment evaluated resistance in selected Phaseolus spp. and soybean genotypes. The range of RAUDPC for Phaseolus spp. was similar to that of soy- bean. The Phaseolus lunatus ‘Bush Baby Lima’ had significantly (P < 0.05) lower RAUDPC than P. vulgaris genotypes evaluated. The cut-stem inoculation technique, which has several advantages over field tests, successfully distinguished differences in aggressiveness among M. phaseolina isolates and relative differences among soybean geno- types for resistance to M. phaseolina comparable with results of field tests.
  
  
  
• 2011: Hartman, G.L., West, E.D., and Herman, T.K. 2011. Crops that feed the World 2. Soybean—worldwide production, use, and constraints caused by pathogens and pests. Food Security 3:5-17. [link]
  
  
• 2011: Twizeyimana, M., Ojiambo, P. S., Haudenshield, J. S., Caetano-Anollés, G., Pedley, K. F., Hartman, G. L., and Bandyopadhyay, R. 2011. Genetic structure and diversity of Phakopsora pachyrhizi isolates from soybean. Plant Pathology. 60: 719-729. [link]
  
  
• 2011: Richardson M., Lagos D., Mitchell R., Hartman G.L., and Voegtlin D.J. 2011. Life history and morphological plasticity of the soybean aphid, Aphis glycines. Entomologia Experimentalis et Applicata 140:139–145. DOI: 10.1111/j.1570-7458.2011.01144.x. [link]
  
  
• 2011: Valdés-López O., Thibivilliers S., Qiu J., Xu W.W., Nguyen T.H., Libault M., Le B.H., Goldberg R.B., Hill C.B., Hartman G.L., Diers B., and Stacey G. 2011. Identification of quantitative trait loci controlling gene expression during the innate immunity response of soybean. Plant Physiology 157(4):1975-86. doi: 10.1104/pp.111.183327. [link]
  
  
• 2011: Twizeyimana M., and Hartman G.L. 2011. Pathogenic variation of Phakopsora pachyrhizi isolates on soybean in the United States from 2006 to 2009. Plant Disease 96:75-81. [link] [view abstract]
  The introduction of Phakopsora pachyrhizi, the cause of soybean rust, into the U.S. is a classic case of a pathogen introduction that became established in a new geographical region on a perennial overwintering host (kudzu). The objective of our study was to classify the pathogenic variation of P. pachyrhizi isolates collected in the U.S., and to determine the spatial and temporal associations therof. A total of 72 isolates of P. pachyrhizi collected from infected kudzu and soybean leaves in the U.S. were purified, and then established and increased on detached soybean leaves. These isolates were tested for virulence and aggressiveness on a differential set of soybean genotypes that included six genotypes with known resistance genes (Rpp), one resistant genotype without any known characterized resistance gene, and a susceptible genotype. Three pathotypes were identified among the 72 U.S. P. pachyrhizi isolates based on the virulence of these isolates on the genotypes in the differential set. Six aggressiveness groups were established based on sporulating uredinia production recorded for each isolate on each soybean genotype. All three pathotypes and all six aggressiveness groups were found in isolates collected from the southern region, from collections made in 2008, and from both hosts (kudzu or soybean). Shannon’s index based on the number of pathotypes, indicated that isolates from the South region were more diverse (H values of 0.83) compared to the isolates collected in other regions. This study establishes a baseline of pathogenic variation of P. pachyrhizi in the U.S. that can be further compared to variation reported in other regions of the world and in future studies that monitor P. pachyrhizi virulence in association to deployment of rust resistance genes.
  
  
  
• 2011: Hartman G.L., Hill C.B., Twizeyimana M., Miles M.R., and Bandyopadhyay R. 2011. Interaction of soybean and Phakopsora pachyrhizi, the cause of soybean rust. CAB Reviews: Perspectives in Agriculture, Veternary Science, Nutrition and Natural Resources 6:1-13. [link]
  
  
• 2011: Paul C., Hill C.B., and Hartman G.L. 2011. Comparisons of visual rust assessments and DNA levels of Phakopsora pachyrhizi in soybean genotypes varying in rust resistance. Plant Disease 95:1007-1012. [download] [view abstract]
  Soybean resistance to Phakopsora pachyrhizi, the cause of soybean rust, has been characterized by the following three infection types: (i) immune response (IM; complete resistance) with no visible lesions, (ii) resistant reaction with reddish brown (RB) lesions (incomplete resistance), and (iii) susceptible reaction with tan-colored (TAN) lesions. Based on visual assessments of these phenotypes, single gene resistance in soybean to P. pachyrhizi has been documented, but colonization within infected tissues based on fungal DNA (FDNA) levels in different soybean genotypes had not been analyzed. The research used a quantitative polymerase chain reaction (Q-PCR) assay to compare visual disease assessment to FDNA in controlled inoculation experiments using two isolates of P. pachyrhizi. The objective of the first experiment was to compare data from digital visual disease assessment to FDNA from Q-PCR assays using digital visual disease assessment using five resistant soybean genotypes (one IM and four RB) and five susceptible genotypes (TAN). The objective of the second experiment was to quantify FDNA using Q-PCR at different time points after inoculation to determine if levels of fungal colonization differed in five soybean genotypes with different levels of resistance (one IM, two RB, and two TAN). For experiment 1, the numbers of uredinia and uredinia per lesion on four of the five resistant soybean genotypes were lower (P < 0.05) than the other six genotypes. Significant differences (P < 0.05) in FDNA concentrations were found among soybean genotypes with TAN lesions and among soybean genotypes with RB lesions. Soybean cultivar UG5 (IM phenotype) had significantly less (P < 0.05) FDNA than all of the other genotypes. Some genotypes that produced TAN lesions had significantly lower (P < 0.05) or non-significantly different FDNA concentrations compared to those genotypes that produced RB lesions. For experiment 2, the regression of FDNA on days after inoculation was significant (P < 0.01) with positive slopes for all genotypes except for UG5, in which FDNA declined over time, indicating a reduction of fungal colonization. The results of this Q-PCR FDNA screening technique demonstrates its use to distinguish different types of resistance, and could be used to facilitate the evaluation of soybean breeding populations, where precise quantification of incomplete and/or partial resistance is needed to identify and map quantitative trait loci.
  
  
  
• 2011: Twizeyimana, M., Ojiambo, P. S., Hartman, G. L., and Bandyopadhyay, R. 2011. Dynamics of soybean rust epidemics in sequential plantings of soybean cultivars in Nigeria. Plant Disease. 95: 43-50. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is an important foliar disease of soybean. Disease severity is dependent on several environmental factors, although the precise nature of most of these factors under field conditions is not known. To help understand the environmental factors that affect disease development, soybean rust epidemics were studied in Nigeria by sequentially planting an early-maturing, highly susceptible cultivar, TGx 1485-1D, and a late-maturing, moderately susceptible cultivar, TGx 1448-2E, at 30- to 45-day intervals from August 2004 to September 2006. Within each planting date, disease onset occurred earlier on TGx 1485-1D than on TGx 1448-2E, and rust onset was at least 20 days earlier on soybean planted between August and October than on soybean planted between November and April. The logistic model provided a better description of the temporal increase in rust severity than the Gompertz model. Based on the logistic model, the highest absolute rates of disease increase were observed on soybean planted in September 2006 and October 2004 for TGx 1485-1D and TGx 1448-2E, respectively. Disease severity as measured by the relative area under disease progress curve (RAUDPC) was significantly (P < 0.05) negatively correlated with evaporation (r = –0.73), solar radiation (r = –0.59), and temperature (r = –0.64) but positively correlated with urediniospore concentration (r = 0.58). Planting date and soybean cultivar significantly (P < 0.05) affected disease severity, with severity being higher on soybean crops planted during the wet season than those planted in the dry season. Within the wet season, planting in May and July resulted in a significantly (P < 0.05) lower RAUDPC than planting between August and October. Yields were significantly (P < 0.001) related to RAUDPC during the wet season, whereby an increase in RAUDPC resulted in a linear decrease in yield. This study suggests that selection of planting date could be a useful cultural practice for reducing soybean rust.
  
  
  
• 2011: Domier L.L., Hobbs H.A., McCoppin N.K., Bowen C.R., Steinlage T.A., Chang S., Wang Y., and Hartman G.L. 2011. Multiple loci condition seed transmission of Soybean mosaic virus (SMV) and SMV-induced seed coat mottling in soybean. Phytopathology 101:750-756. [download] [view abstract]
  Infection of soybean plants with Soybean mosaic virus (SMV), which is transmitted by aphids and through seed, can cause significant reductions in seed production and quality. Because seedborne infections are the primary sources of inoculum for SMV infections in North America, host-plant resistance to seed transmission can limit the pool of plants that can serve as sources of inoculum. To examine the inheritance of SMV seed transmission in soybean, crosses were made between plant introductions (PIs) with high (PI88799), moderate (PI60279), and low (PI548391) rates of transmission of SMV through seed. In four F₂ populations, SMV seed transmission segregated as if conditioned by two or more genes. Consequently, a recombinant inbred line population was derived from a cross between PIs 88799 and 548391 and evaluated for segregation of SMV seed transmission, seed coat mottling, and simple sequence repeat markers. Chromosomal regions on linkage groups C1 and C2 were significantly associated with both transmission of isolate SMV 413 through seed and SMV-induced seed coat mottling, and explained ≈42.8 and 46.4% of the variability in these two traits, respectively. Chromosomal regions associated with seed transmission and seed coat mottling contained homologues of Arabidopsis genes DCL3 and RDR6, which encode enzymes involved in RNA-mediated transcriptional and posttranscriptional gene silencing.
  
  
  
• 2011: Miles M.R., Bonde M.R., Nester S.E., Berner D.K., Frederick R.D., and Hartman G.L. 2011. Characterizing resistance to Phakopsora pachyrhizi in soybean. Plant Disease 95:577-581. [download] [view abstract]
  Resistance in soybean to Phakopsora pachyrhizi, the cause of soybean rust, is characterized by either reddish-brown (RB) lesions or an immune response. The RB type of resistance can be incomplete, as evidenced by the presence of sporulating uredinia within lesions. Susceptibility, on the other hand, is exemplified by tan-colored (TAN) lesions, and can be expressed in gradations of susceptibility or partial resistance that are less well defined. This study evaluated traits associated with incomplete or partial resistance to P. pachyrhizi in soybean by comparing 34 soybean accessions inoculated with four P. pachyrhizi isolates. Six accessions produced RB lesions to all four isolates, while 19 accessions produced TAN lesions, including plant introduction (PI) 200492 (Rpp1) and the susceptible check ‘Williams’. Williams had among the largest area under the disease progress curve (AUDPC) values and area under the sporulating uredinia progress curve (AUSUPC) values, while eight accessions had lower AUSUPC values. Of the known sources of single-gene resistance, only PI 230970 (Rpp2), PI 459025B (Rpp4), and PI 594538A (Rpp1b) had lower AUDPC and AUSUPC values than Williams. PI 594538A and PI 561356 had RB lesions and had the lowest AUDPC and AUSUPC values. Of the known sources of single-gene resistance, only PI 230970 (Rpp2) and PI 594538A (Rpp1b) produced fewer and smaller-diameter uredinia than Williams. This study characterized reactions to P. pachyrhizi in 34 accessions based on lesion type and sporulation, and defined incomplete resistance and partial resistance in the soybean–P. pachyrhizi interaction.
  
  
  
• 2011: Walker D., Boerma H., Phillips D., Schneider R., Buckley J., Shipe E., Mueller J., Weaver D., Sikora E., Moore S., Hartman G., Miles M.R., Harris D., Wright D.L., Marois J.J., and Nelson R.L. 2011. Evaluation of USDA soybean germplasm accessions for resistance to soybean rust in the Southern United States. Crop Science 51:678-693. [download] [view abstract]
  Soybean [Glycine max (L.) Merr.] resistance to soybean rust (SBR) caused by Phakopsora pachyrhizi could reduce reliance on fungicides to manage this disease. The objective of this study was to identify soybean germplasm with resistance to field populations of P. pachyrhizi in the United States. Field evaluations of 576 accessions from the USDA Soybean Germplasm Collection for resistance to SBR were conducted at seven locations in the southern United States between 2006 and 2008. Accessions from maturity groups (MG) 000 to X and North American susceptible check cultivars from each MG except X were rated for disease severity in all year–location environments, and for disease incidence, fungal sporulation, lesion type, and/or uredinia density in certain environments. While none of the accessions was immune in all environments, 64 were resistant in two or more locations each year that they were tested. Some accessions appeared to be more resistant in certain environments than in others. Of the original four Rpp genes described in the literature, Rpp1 provided the highest level of resistance, and among the accessions with uncharacterized Rpp genes, PI 567104B had the highest overall resistance across environments. The plant introductions confirmed to be resistant in these evaluations should be useful sources of genes for resistance to North American populations of P. pachyrhizi.
  
  
  
• 2011: Haudenshield, J. S. and Hartman, G.L. 2011. Exogenous controls increase negative call veracity in multiplexed, quantitative PCR assays for Phakopsora pachyrhizi. Plant Disease 95: 343-352. [download] [view abstract]
  Quantitative polymerase chain reaction (Q-PCR) utilizing specific primer sequences and a fluorogenic, 5′-exonuclease linear hydrolysis probe is well established as a detection and identification method for Phakopsora pachyrhizi and P. meibomiae, two rust pathogens of soybean. Because of the extreme sensitivity of Q-PCR, the DNA of single urediniospores of these fungi can be detected from total DNA extracts of environmental samples. However, some DNA preparations unpredictably contain PCR inhibitors that increase the frequency of false negatives indistinguishable from true negatives. Three synthetic DNA molecules of arbitrary sequence were constructed as multiplexed internal controls (ICs) to cull false-negative results by producing a positive signal to validate the PCR process within each individual reaction. The first two, PpaIC and PmeIC, are a single-stranded oligonucleotide flanked by sequences complementary to the primers of either the P. pachyrhizi or P. meibomiae primary assay but hybridizing to a unique fluorogenic probe; the third contains unique primer- and probe-binding sequences, and was prepared as a cloned DNA fragment in a linearized plasmid. These ICs neither qualitatively nor quantitatively affected their primary assays. PpaIC and PmeIC were shown to successfully identify false-negative reactions resulting from endogenous or exogenous inhibitors, and can be readily adapted to function in a variety of diagnostic Q-PCR assays; the plasmid was found to successfully validate true negatives in similar Q-PCR assays for other soybean pathogens, as well as to function as a tracer molecule during DNA extraction and recovery.
  
  
  
• 2010: Pham, T.A., C. B. Hill, M. R. Miles, B. T. Nguyen, T. T. Vu, T. D. Vuong , T. T. VanToai, H. T. Nguyen, and G. L. Hartman. 2010. Evaluation of soybean for resistance to soybean rust in Vietnam. Field Crops Research 117:131-138. [link]
  
  
• 2010: Soria-Guerra R.E., Rosales-Mendoza S., Chang S., Haudenshield J.S., Zheng D., Rao S.S., Hartman G.L., Ghabrial S.A., and Korban S.S. 2010. Identifying differentially expressed genes in leaves of Glycine tomentella in the presence of the fungal pathogen Phakopsora pachyrhizi. Planta 232:1181–1189. [link]
  
  
• 2010: Soria-Guerra R.E., Rosales-Mendoza S., Chang S., Haudenshield J.S., Padmanaban A., Rodriguez-Zas S., Hartman G.L., Ghabrial S.A., and Korban S.S. 2010. Transcriptome analysis of resistant and susceptible genotypes of Glycine tomentella during Phakopsora pachyrhizi infection reveals novel rust resistance genes. Theor Appl Genet 120:1315–1333. [link]
  
  
• 2010: Tang E., Hill C.B., and Hartman G.L. 2010. Carbon utilization profiles of Fusarium virguliforme isolates. Canadian Journal of Microbiology 56:979-986. [link]
  
  
• 2010: Hartman, G.L. and C.B. Hill. 2010. Diseases of Soybean and their Management. Pages 276-299 in "Soybean: Botany, Production, and Uses," Guriqbal Singh, Ed., CAB International, Wallingford, UK and Cambridge, MA. [link]
  
  
• 2010: Kim, K.-S., C.B. Hill, G.L. Hartman, D. Hyten, M.E. Hudson, and B.W. Diers. 2010. Fine mapping of the soybean aphid resistance gene Rag2 in soybean PI 200538. Theoretical Applied Genetics 121: 599-610. [link]
  
  
• 2010: Kim, K.S., S. Bellendir, K.A. Hudson, C.B. Hill, G.L. Hartman, D.L. Hyten, M.E. Hudson and B.W. Diers. 2010. Fine mapping the soybean aphid resistance gene Rag1 in soybean. Theoretical & Applied Genetics 120:1063-1071. [link]
  
  
• 2010: Paul C., Bowen C.R., Bandyopadhyay R., Tefera H., Adeleke R., Sikora E., Pegues M.D., and Hartman G.L. 2010. Registration of three soybean germplasm lines resistant to Phakopsora pachyrhizi (soybean rust). Journal of Plant Registrations 4:244-248. doi:10.3198/jpr2009.07.0413crg. [link]
  
  
• 2010: Cui D., Zhang Q., Li M., Hartman G.L., and Zhao Y. 2010. Image processing methods for quantitatively detecting soybean rust from multispectral images. Biosystems Engineering 107:186-193. [link]
  
  
• 2010: Bradley, C., Hines, R., Haudenshield, J.S., Hartman, G.L. 2010. First report of soybean rust, caused by Phakopsora pachyrhizi, on kudzu (Pueraria montana var. lobata) in Illinois. Plant Disease 94:477. [link] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi Syd., first was observed in the continental United States during 2004 on soybean (Glycine max (L.) Merr.) in Louisiana (4), and on kudzu (Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen & Almeida) in Florida (2). Kudzu is a leguminous weed that is prevalent in the southern United States with its range extending northward into other states including Illinois. In October 2009, a kudzu patch located in Pulaski County in southern Illinois was investigated for the presence of soybean rust. Twenty-five leaflets were collected, and the abaxial sides of leaflets were evaluated visually for the presence of uredinia with a dissecting microscope. Uredinia and urediniospores were found on two leaflets. When viewed with a compound microscope, urediniospores were hyaline, echinulate, and measured 20 × 25 μm. On the basis of uredinia and urediniospores, the disease tentatively was identified as soybean rust caused by P. pachyrhizi. To confirm the identification, one leaflet with pustules was assayed with a Soybean Rust QuickStix Diagnostic Kit (Envirologix, Portland, ME). For the other leaflet, the area of the pustule was excised (approximately 28 mm2) and an area of the leaflet at the margin on the opposite half of the leaflet with no visible pustule (approximately 54 mm2) was excised. DNA was extracted from the excised areas of the leaflet for confirmation by quantitative PCR (Q-PCR) using primers and probe specific to P. pachyrhizi and P. meibomiae (Arthur) Arthur (1). Both the QuickStix Diagnostic Kit and the Q-PCR confirmed the diagnosis as soybean rust caused by P. pachyrhizi. Q-PCR also suggested the presence of a nonsporulating latent rust infection on the same kudzu leaflet at the margin on the opposite side of the midrib. Soybean rust first was confirmed on soybean in Illinois in 2006 (3), but to our knowledge, this is the first observation of the disease on kudzu in the state. This report confirms that at least some kudzu plants in Illinois are susceptible to soybean rust and that latent kudzu infection may exist without outward signs of the fungus. Currently, this is the most northern observation of soybean rust on kudzu in North America. It is unknown what role, if any, Illinois kudzu will play in the epidemiology of soybean rust in the state. Since kudzu tops die after the first frost, there is no expectation of P. pachyrhizi to overwinter in Illinois on kudzu as it does in some states adjacent to the Gulf of Mexico.
  
  
  
• 2010: Lygin, A. V., Hill, C. B., Zernova, O. V., Crull, L., Widholm, J. M., Hartman, G. L., and Lozovaya, V. V. 2010. Response of soybean pathogens to glyceollin. Phytopathology 100:897-903. [download] [view abstract]
  Plants recognize invading pathogens and respond biochemically to prevent invasion or inhibit colonization in plant cells. Enhancing this response in crop plants could improve sustainable methods to manage plant diseases. To enhance disease resistance in soybean, the soybean phytoalexin glyceollin was assessed in soybean hairy roots of two soybean genotypes, Spencer and PI 567374, transformed with either soybean isoflavone synthase (IFS2) or chalcone synthase (CHS6) genes that were inoculated with the soybean pathogens Diaporthe phaseolorum var. meridionales, Macrophomina phaseolina, Sclerotinia sclerotiorum, and Phytophthora sojae. The hairy-root-transformed lines had severalfold decreased levels of isoflavone daidzein, the precursor of glyceollin, and considerably lower concentrations of glyceollin induced by pathogens measured 5 days after fungal inoculation compared with the nontransformed controls without phenolic transgenes. M. phaseolina, P. sojae, and S. sclerotiorum grew much more on IFS2- and CHS6-transformed roots than on control roots, although there was no significant difference in growth of D. phaseolorum var. meridionales on the transformed hairy-root lines. In addition, glyceollin concentration was lower in D. phaseolorum var. meridionales-inoculated transformed and control roots than roots inoculated with the other pathogens. Glyceollin inhibited the growth of D. phaseolorum var. meridionales, M. phaseolina, P. sojae, S. sclerotiorum, and three additional soybean pathogens: Cercospora sojina, Phialophora gregata, and Rhizoctonia solani. The most common product of glyceollin conversion or degradation by the pathogens, with the exception of P. sojae, which had no glyceollin degradation products found in the culture medium, was 7-hydroxyglyceollin.
  
  
  
• 2010: Li, S., Hartman, G. L., and Boykin, D. L. 2010. Aggressiveness of Phomopsis longicolla and other Phomopsis spp. on soybean. Plant Dis. 94:1035-1040. [download] [view abstract]
  Phomopsis seed decay of soybean is a major cause of poor-quality soybean seed. The disease is caused primarily by the fungal pathogen Phomopsis longicolla. Aggressiveness of isolates of P. longicolla from soybean and other Phomopsis spp. from other hosts were compared by inoculating 2-week-old soybean plants of cv. Williams 82. There were significant (P ≤ 0.0001) differences among isolates based on stem length and stem lesion length. The P. longicolla soybean isolate PL16, from Mississippi, caused the shortest stem length while the non-soybean isolate P9, from Illinois, caused the greatest stem lesion length. The type isolate of P. longicolla, PL31 (Fau 600), was one of the 3 most aggressive isolates among all 48 isolates tested. The velvetleaf isolate P9 was the most aggressive among 13 isolates from non-soybean hosts. This study provided the first evaluation of aggressiveness of P. longicolla isolates from different geographic origins and the first demonstration that Phomopsis spp. isolated from cantaloupe, eggplant, and watermelon infected soybean. Knowledge about the variability of the pathogen is important for selecting isolates for breeding soybean lines with broad-based resistance to Phomopsis seed decay.
  
  
  
• 2010: Twizeyimana, M., and Hartman, G. L. 2010. Culturing Phakopsora pachyrhizi on detached leaves and urediniospore survival at different temperatures and relative humidities. Plant Disease 94: 1453-1460. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important foliar diseases of soybean worldwide. In a series of experiments, multiple objectives were addressed to determine the (i) longevity of detached soybean leaves, (ii) reproductive capacity of uredinia on leaves inoculated and/or incubated on the abaxial versus adaxial side of the leaf, (iii) reproductive capacity of uredinia and urediniospore germination when spores were harvested at regular intervals or all at once, and (iv) effect of temperature and relative humidity (RH) on urediniospore germination. A detached-leaf assay using agar medium amended with 6-benzylaminopurine performed better in retarding leaf chlorosis than filter paper alone among five soybean genotypes. Among the three susceptible genotypes tested, detached leaves of cv. Williams 82 had the lowest level of leaf chlorosis and often allowed for the greatest urediniospore production and germination rate. Temperature and RH played significant roles in survival of urediniospore as measured by germination rates. Viable urediniospores were harvested from infected soybean leaves maintained at room temperature (23 to 24°C at 55 to 60% RH) for up to 18 days, whereas freshly harvested urediniospores that were desiccated for 12 h before being placed in vials and maintained at room temperature remained viable for up to 30 days. Urediniospore hydration was the major factor for the dormancy reversion; thermal shock with hydration and no thermal shock with hydration treatments had consistently similar urediniospore germination rates. In the RH experiment, urediniospores harvested from inoculated leaf pieces maintained at 85% RH had the highest germination rates compared with higher and lower RH. Improvement in P. pachyrhizi cultural techniques and understanding of urediniospore survival will enhance our knowledge of the pathogen biology, host-plant relationship, and conditions that favor the infection, reproduction, and survival of the pathogen.
  
  
  
• 2010: Slaminko, T. L., Bowen, C. R., and Hartman, G. L. 2010. Multi-year evaluation of commercial soybean cultivars for resistance to Phytophthora sojae. Plant Dis. 94:368-371. [download] [view abstract]
  Phytophthora sojae causes damping-off, root rot, and stem rot of soybean, particularly in poorly drained soils. Soybean cultivar resistance is one of the primary methods to control this disease, with Rps1c, Rps1k, and Rps1a being the most commonly used genes. The Varietal Information Program for Soybeans (VIPS) at the University of Illinois evaluates soybean cultivars for resistance to a number of diseases including Phytophthora root rot (PRR). The objectives of this research were to evaluate PRR resistance among commercial cultivars or advanced lines, and to compare these results with the information on PRR resistance provided by the company that entered the cultivar in VIPS. Each year from 2004 to 2008, between 600 and 900 cultivars were evaluated for resistance to either race 17 or 26 of P. sojae using the hypocotyl inoculation method. P. sojae single resistance genes were reported in 1,808 or 51% of the entries based on company information. Of these, the most commonly reported resistance genes were Rps1c (50%), Rps1k (40%), and Rps1a (10%). To a much smaller degree, companies reported using Rps3a (0.3%), Rps1b (0.2%), and Rps7 (0.2%). For the duration of the 5-year testing period, almost half of the cultivars (46%) were entered in VIPS with no reported resistance genes, and only nine out of a total of 3,533 entries (less than 0.3%) reported a stacked combination of resistance genes. Agreement between company-reported genes and any resistance found in the VIPS PRR evaluation was highest for those cultivars claiming to have Rps1c (90%) and Rps1k (83%), followed by Rps1a (70%). On average, 54% of the cultivars submitted to VIPS each year were new, reflecting the rapid development and turnover of soybean cultivars provided by the soybean seed companies.
  
  
  
• 2010: Hobbs, H. A., Herman, T. K., Slaminko, T. L., Wang, Y., Nguyen, B. T., McCoppin, N. K., Domier, L. L. and Hartman, G. L. 2010. Occurrences of soybean viruses, fungal diseases, and pests in Illinois soybean rust sentinel plots. Online. Plant Health Progress doi:10.1094/PHP-2010-0827-01-BR. [download] [view abstract]
  After soybean rust was confirmed in soybean in the USA, sentinel plots were established in 26 states to monitor its spread. Funding for establishing, sampling, and monitoring the plots came from the USDA, national, regional, and state soybean commodity boards, and state departments of agriculture, extension services, and universities. The presence of sentinel plots for soybean rust monitoring provided the potential for reducing the time and expense of extensive statewide travel for collection of soybean leaf samples for monitoring the incidence of other foliar diseases of soybean in Illinois.
  
  
  
• 2010: Ma, J., Hill, C. B., and Hartman, G. L. 2010. Production of Macrophomina phaseolina conidia by multiple soybean isolates in culture. Plant Dis. 94:1088-1092. [download] [view abstract]
  Macrophomina phaseolina is the cause of charcoal rot of soybean (Glycine max). Resistance to M. phaseolina in commercial soybean cultivars is not common but is needed in locations where the disease is chronic and severe. The objective of this study was to develop a reliable method to produce sufficient M. phaseolina conidia that can be used to inoculate soybean plants in a highthroughput resistance-screening program. Production of pycnidia is not common on most culture media, such as potato dextrose agar, but can be produced on media containing plant parts or oilseed extracts. Seven semi-defined media were tested to induce pycnidia production. Results indicated that the number of pycnidia that were produced by eight M. phaseolina isolates was dependent on induction medium; however, peanut butter extract-saturated filter paper placed over soynut butter extract agar (PESEA) allowed for greater pycnidia and conidia production than the other media tested. Production of pycnidia on PESEA ranged from 269 to 1,082 per plate. There were no differences among isolates in germination of conidia produced on PESEA, which averaged 83 ± 2% germination. A conidial suspension from one M. phaseolina isolate produced on PESEA and inoculated onto soybean radicles significantly distinguished (P < 0.01) ‘DT97-4290’, a soybean genotype with partial resistance to charcoal rot, from a susceptible genotype, ‘LS98-0358’. Results of this study indicated that multiple isolates of M. phaseolina from soybean produced sufficient amounts of conidia on PESEA to use as inoculum. This conidia inoculum production method will facilitate soybean charcoal rot resistance screening evaluation with different soybean isolates.
  
  
  
• 2009: Hartman, G.L. and Haudenshield, J. S. 2009. Movement of Phakopsora pachyrhizi (soybean rust) spores by non-conventional means. European Journal of Plant Pathology 123:225–228. [link]
  
  
• 2009: Goradia, L., G.L. Hartman, and S.L. Daniel. 2009. Evaluation of glyphosate-resistant soybean cultivars for resistance to bacterial pustule. European Journal of Plant Pathology 124:331-335. [link]
  
  
• 2009: Calla, B., Voung, T., Radwin, O., Hartman, G.L., and Clough, S.J. 2009. Gene expression profiling soybean stem tissue early response to Sclerotinia sclerotiorum and in silico mapping in relation to resistance markers. Plant Genome 2:149-166. [link]
  
  
• 2009: Cui, D., Q. Zhang, M. Li, Y. Zhao, and G.L. Hartman. 2009. Detection of soybean rust using a multispectral image sensor. Sens. Instrum. Food Qual. Saf. 3:49-56. [link]
  
  
• 2009: Pham, T. A., Miles, M. R., Frederick, R. D., Hill, C. B., and Hartman, G. L. 2009. Differential responses of resistant soybean entries to isolates of Phakopsora pachyrhizi. Plant Disease 93:224-228. [download] [view abstract]
  Soybean rust, caused by the fungus Phakopsora pachyrhizi, was detected in the continental United States in 2004. Several new sources of resistance to P. pachyrhizi have been identified in soybean (Glycine max); however, there is limited information about their resistance when challenged with additional U.S. and international isolates. Resistance of 20 soybean (G. max) entries was compared after inoculation with 10 P. pachyrhizi isolates, representing different geographic and temporal origins. Soybean entries included 2 universal susceptible cultivars, 4 sources of soybean rust resistance genes (Rpp1–4), and 4 and 10 resistant entries selected from field trials in Paraguay and Vietnam, respectively. Of the known Rpp1–4 sources of resistance, plant introduction (PI) 459025B (Rpp4) produced reddish-brown (RB) lesions in response to all of the P. pachyrhizi isolates, while PI 230970 (Rpp2) produced RB lesions to all isolates except one from Taiwan, in response to which it produced a susceptible tan (TAN) lesion. PI 200492 (Rpp1) and PI 462312 (Rpp3) produced TAN lesions in response to most P. pachyrhizi isolates. The resistant entries selected from Paraguay and Vietnam varied considerably in their responses to the 10 P. pachyrhizi isolates, with M 103 the most susceptible and GC 84058-18-4 the most resistant. The reaction patterns on these resistant entries to the P. pachyrhizi isolates were different compared with the four soybean accessions with the Rpp genes, indicating that they contain novel sources of rust resistance. Among the P. pachyrhizi isolates, TW 72-1 from Taiwan and IN 73-1 from India produced the most susceptible and resistant reactions, respectively, on the soybean entries.
  
  
  
• 2009: Paul, C., and G.L. Hartman. 2009. Sources of soybean rust resistance challenged with single-spored isolates of Phakopsora pachyrhizi collected from the USA. Crop Sci. 49: 1781-1785. [download] [view abstract]
  Soybean rust, caused by the fungus Phakopsora pachyrhizi Syd., is a potentially devastating disease that can cause significant yield losses. Resistance in soybean [Glycine max (L.) Merr.] germplasm, both qualitative and quantitative, may be effective in providing at least partial control of soybean rust. A number of soybean genotypes have resistance to soybean rust, but few of these have been challenged with the recently recovered U.S. isolates. The objective of this study was to evaluate known sources of soybean rust resistance against U.S. isolates of P. pachyrhizi. Twenty-eight soybean genotypes that either contained known major-genes for resistance or had been reported as new sources of soybean rust resistance, along with two susceptible checks, were challenged with six P. pachyrhizi isolates collected in the U.S. All six isolates produced similar phenotypic reactions within each of the genotypes. Five genotypes, including the Rpp1 source and the isoline of ‘Williams 82’ with Rpp1, had no visible lesions. Eleven genotypes produced red-brown lesions with few uredinia, including the sources of Rpp2 and Rpp3, and the remainder had susceptible tan lesions, including the source of resistance for Rpp4. Uredinial counts from genotypes producing red-brown lesions on live and fi xed leafl ets showed significant variation in the number of uredinia with a genotype × isolate interaction. Uredinial counts from genotypes producing tan lesions on live and fixed leaflets showed signifi cant variation in the number of uredinia among genotypes, but there was no genotype × isolate interaction. There were signifi cant correlations (r = 0.8, P < 0.0001; and r = 0.4, P < 0.0001) between uredinial counts based on live and fixed leaflets within genotypes producing red-brown lesions and those producing tan lesions, respectively.
  
  
  
• 2009: Twizeyimana, M., P.S. Ojiambo, K. Sonder, T. Ikotun, G.L. Hartman, and R. Bandyopadhyay. 2009. Pathogenic variation of Phakopsora pachyrhizi infecting soybean in Nigeria. Phytopathology 99:353-361. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is an important disease in Nigeria and many other soybean-producing countries world-wide. To determine the geographical distribution of soybean rust in Nigeria, soybean fields were surveyed in the Derived Savanna (DS), Northern Guinea Savanna (NGS), and Southern Guinea Savanna (SGS) agroecological zones in Nigeria between 2004 and 2006. Disease severity in each zone was determined and analyzed using geostatistics. Prevalence of infected fields and disease severity in surveyed fields were significantly (P < 0.05) different between geographical zones with both variables being higher in the DS zone than in either NGS or SGS zones. Geostatistical analysis indicated that the spatial influence of disease severity at one location on severity at other locations was between 75 and 120 km. An exponential model best described the relationship between semivariance and lag distance when rust severity was high. Spatial interpolation of rust severity showed that locations in the DS zone were more conducive for the rust epidemic compared to areas in the NGS zone. In the 2005 survey, 116 purified isolates were established in culture on detached soybean leaves. To establish the nature of pathogenic variation in P. pachyrhizi, a set of four soybean accessions with Rpp(1), Rpp(2), Rpp(3), and Rpp(4) resistance genes, two highly resistant and two highly susceptible genotypes were inoculated with single uredinial isolates. Principal component analysis on the number of uredinia per square centimeter of leaf tissue for 116 isolates indicated that an adequate summary of pathogenic variation was obtained using only four genotypes. Of these four, PI 459025B (with Rpp(4) gene) and TG× 1485-1D had the lowest and highest number of uredinia per square centimeter, respectively. Based on cluster analysis of the number of uredinia per square centimeter, seven pathotype clusters were determined. Isolates in cluster III were the most virulent, while those in cluster IV were the least virulent. Shannon’s index (H) revealed a more diverse pathogen population in the DS zone (H = 1.21) compared to the rust population in SGS and NGS with H values of 1.08 and 0.91, respectively. This work will be useful in breeding and management of soybean rust by facilitating identification of resistant genotypes and targeting cultivars with specific resistance to match prevailing P. pachyrhizi pathotypes in a given geographical zone.
  
  
  
• 2009: Hill, C.B., K.S. Kim, L. Crull, B.W. Diers, and G.L. Hartman. 2009. Inheritance of resistance to the soybean aphid in soybean PI200538. Crop Science 49: 1193-1200. [download] [view abstract]
  The soybean aphid (Aphis glycines Matsumura) is a major soybean [Glycine max (L.) Merr.] insect pest. Soybean plant introduction (PI) 200538 has strong resistance to the aphid. The objectives of our research were to determine the inheritance of resistance and to map gene(s) controlling resistance in PI 200538. F₂ populations developed from crosses between PI 200538 and three susceptible genotypes were tested for resistance and with DNA markers. F₂ plants from the cross ‘Ina’ × PI 200538 segregated 114 resistant to 37 susceptible and F₂ plants from the cross ‘Williams 82’ × PI 200538 segregated 203 resistant to 65 susceptible when tested for resistance to soybean aphid biotype 1. F₂ plants from the cross LD02-4485 × PI 200538 segregated 167 resistant to 62 susceptible when tested for resistance to biotype 2. These populations fit a 3:1 genetic ratio (P = 0.89, 0.78, and 0.52, respectively) with resistance dominant over susceptibility. Segregation among F_2:3 families from the crosses supported the dominant resistance gene hypothesis. The gene mapped to soybean linkage group F, flanked by the simple sequence repeat marker loci Satt510, Soyhsp176, Satt114, and Sct_033, located in the same region as the aphid resistance gene Rag2. Since the resistance gene in PI 200538 also gave resistance to soybean aphid biotypes 1 and 2, it is possible that the gene is Rag2 and not a new aphid resistance gene. Therefore, PI 200538 may be an additional source of Rag2.
  
  
  
• 2009: Mueller, T. A., Miles, M. R., Morel, W., Marois, J. J., Wright, D. L., Kemerait, R. C., Levy, C., and Hartman, G. L. 2009. Effect of fungicide and timing of application on soybean rust severity and yield. Plant Disease 93:243-248. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is a devastating foliar disease of soybean that may cause significant yield losses if not managed by well-timed fungicide applications. To determine the effect of fungicide timing on soybean rust severity and soybean yield, field trials were completed in Paraguay (four locations), the United States (two locations), and Zimbabwe (one location) from 2005 to 2006. Treatments at each location included applications of tebuconazole, pyraclostrobin, or a combination of azoxystrobin + propiconazole, and in some locations pyraclostrobin + tebuconazole at the following soybean growth stages (GS): (i) GS R1 (beginning flowering), (ii) GS R3 (beginning pod), (iii) GS R5 (beginning seed), (iv) GS R1 + R3, (v) GS R3 + R5, and (vi) GS R1 + R3 + R5. Soybean yields from plots treated with fungicides were 16 to 114% greater than yields from no fungicide control plots in four locations in Paraguay, 12 to 55% greater in two locations in the United States, and 31% greater in Zimbabwe. In all locations, rust severity measured over time as area under the disease progress curve (AUDPC) was negatively correlated (r = –0.3, P < 0.0001) to yield. The effectiveness of any given treatment (timing of application and product applied) was often dependent on when rust was first detected and the intensity of its development. For example, when soybean rust was first observed before GS R3 (two locations in Paraguay), the plants in plots treated with a fungicide at GS R1 had the lowest AUPDC values and highest yields. When soybean rust was first observed after GS R3, plants treated with a fungicide at GS R3 and/or GS R5 had the lowest AUDPC values and highest yields with a few exceptions.
  
  
  
• 2009: Chakraborty, N., J. Curley, R.D. Frederick, D.L. Hyten, R.L. Nelson, G.L. Hartman, and B.W. Diers. 2009. Mapping and confirmation of a new allele at Rpp1 from soybean PI 504538A conferring RB lesion type resistance to soybean rust. Crop Science 49:783-790. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi (H. Sydow & Sydow), is a destructive soybean [Glycine max (L.) Merr.] disease and identification of new resistance genes is essential for effective rust management. Our research objectives were to map and confirm the location of resistance gene(s) in PI 594538A using a population of 98 F_3:4 lines from a cross between PI 594538A (reddish-brown [RB] lesions) and the susceptible cultivar Loda (tan [TAN] lesions). The lines were inoculated with the P. pachyrhizi isolate ZM01-1 from Zimbabwe. The RB resistance in PI 594538A mapped on linkage group G as a single dominant gene. This gene is likely an allele of Rpp1 or a new closely linked gene because it mapped within 1 cM of Rpp1 and ZM01-1 produced RB lesions on PI 594538A and TAN lesions on PI 200492, the original source of Rpp1. The mapping of the new Rpp1 allele, named Rpp1-b, was confirmed in a second population.
  
  
  
• 2009: Li, S., G.L. Hartman, and Y. Chen. 2009. Evaluation of aggressiveness of Fusarium virguliforme isolates that cause sudden death syndrome. Journal of Plant Pathlogy 91:77-86. [download] [view abstract]
  Fusarium virguliforme (Akoi, O’Donnell, Homma & Lattanzi), formerly named F. solani (Mart.) Sacc. f.sp. glycines, is the cause of soybean sudden death syndrome (SDS). Over the last 6 years, an international collection of F. virguliforme isolates has been established and maintained at the National Soybean Pathogen Collection Center, University of Illinois at Urbana-Champaign. Using part of the collection, aggressiveness of F. virguliforme isolates to a susceptible soybean cultivar, Great Lakes 3202, was evaluated under controlled conditions in the greenhouse. After an initial evaluation of 123 isolates on soybean, 30 isolates from different geographic origins with different levels of foliar severity were selected to further evaluate both foliar and root severities. Variability of aggressiveness based on measurements of SDS foliar severity, shoot, root, and root lesion lengths, shoot and root dry weights, and total dry weights was found among isolates (P ≤ 0.01). Isolate FSG1(Mont-1), a reference isolate that has been widely used by the soybean community for basic and applied research, caused the greatest reduction in shoot weight and shoot length compared to the non-inoculated control plants, but six isolates caused higher foliar severity and 15 isolates caused longer root lesion length than the isolate FSG1. Isolate FSG5 caused the greatest reduction in root weight among isolates. Knowledge about the variability of the pathogen is important for selection of isolates for testing for broadbased SDS resistant soybean lines.
  
  
  
• 2008: Slaminko, T. L., Miles, M. R., Marois, J. J., and Hartman, G. L. 2008. Hosts of Phakopsora pachyrhizi identified in field evaluations in Florida. Online. Plant Health Progress doi:10.1094/PHP-2008-1103-01-RS. [link] [view abstract]
  Phakopsora pachyrhizi, the causal organism of soybean rust, was first found on Glycine max in the continental United States in 2004, and subsequently on Pueraria lobata, Desmodium tortuosum, three Phaseolus species, and Erythrina herbacea in the field. The pathogen has been reported to occur on over 150 legume species worldwide, and it is likely to infect native and introduced legume species in the USA. The objective of this study was to determine if USA-native or -naturalized legume species could become infected with P. pachyrhizi in field conditions. A total of 80 accessions representing 52 species in 29 genera were infected in the field trials. Crotalaria retusa, Lathyrus latifolius, Phaseolus angustissimus, P. polystachios, and Robinia hispida are new hosts. This is the first report showing the broad host range of P. pachyrhizi based on field infections in the USA. Some of these hosts grow in the southern USA, and could, like kudzu, overwinter P. pachyrhizi.
  
  
  
• 2008: Li, S., G.L. Hartman, L.L. Domier, and D. Boykin. 2008. Quantification of Fusarium solani f. sp. glycines isolates in soybean roots by colony-forming unit assays and real-time quantitative PCR. Theoretical and Applied Genetics 117:343-352. [link]
  
  
• 2008: Farias Neto, A.L., M. Schmidt, G.L. Hartman, S. Li, and B.W. Diers. 2008. Inoculation methods under greenhouse conditions for evaluating soybean resistance to sudden death syndrome. Pesquisa Agropecuária Brasileira 43:1475-1482. [link] [view abstract]
  The objectives of this work were to evaluate two greenhouse screening methods for sudden death syndrome (SDS) and to determine which one is best correlated with field resistance of soybean genotypes. The evaluations were done with three sets of genotypes that were classified as partially resistant, intermediate, and susceptible to SDS based on previous field evaluations. These three sets were independently evaluated for greenhouse SDS reactions using cone and tray inoculation methods. Plants were infected using grains of white sorghum [Sorghum bicolor (L.) Moench] infested with Fusarium solani f. sp. glycines. Foliar symptom severity was rated 21 days after emergence. The cone and field SDS ratings were significantly correlated and ranged from 0.69 for set 1 to 0.51 for set 3. Correlations of SDS ratings of genotypes between field and greenhouse tray ratings were significant for set 1 and not significant for set 2. The cone method showed the highest correlation with field results and is recommended to screen soybean genotypes for SDS resistance.
  
  
  
• 2008: Wille, B. D., and Hartman, G. L. 2008. Evaluation of artificial diets for rearing Aphis glycines (Hemiptera: Aphididae). Journal of Economic Entomology 101:1228-1232. [download] [view abstract]
  Artificial aphid diets have been previously developed for the pea aphid, Acyrthosiphon pisum (Harris), and the green peach aphid, Myzus persicae (Sulzer). The ability to rear aphids on an artificial diet allows for selectively adding or subtracting compounds from an aphid's food source to determine the effect on fecundity and longevity. Five diets previously developed for the green peach aphid and the pea aphid were tested for their suitability for rearing soybean aphid, Aphis glycines Matsumura. The best diet, originally developed for the green peach aphid and based on the amino acid profile of young potato plants, allowed 12 generations of soybean aphids to develop. For all diets tested, aphid fecundity, and longevity were greatly reduced in comparison with aphids reared on soybean, Glycine max (L.) Merr., plants or on detached soybean leaves. In addition, mean developmental time was significantly longer for aphids reared on artificial diets.
  
  
  
• 2008: Kim, K. S., Hill, C. B., Hartman, G. L., Mian, M. A. R., and Diers, B. W.2008. Discovery of soybean aphid biotypes. Crop Science 48:923-928. [download] [view abstract]
  The soybean aphid [Aphis glycines Matsumura (Hemiptera: Aphididae)] is an invasive insect pest of soybean [Glycine max (L.) Merr.] that was first reported in North America in 2000. There are currently no reports of soybean aphid biotype diversity and this information is needed before aphid resistance genes are deployed. The objective of this research was to test for aphid biotype variation. The response of two A. glycines isolates, one collected in Ohio and the other in Illinois, were compared by infesting eight soybean genotypes in nonchoice tests. The same genotypes also were tested with the Ohio isolate using a choice test. In the nonchoice test, there was a significant (P < 0.0001) effect of aphid isolate, genotype, and a significant aphid isolate by soybean genotype interaction for the number of aphids per plant 10 and 15 d after infestation. The responses of the eight genotypes to the Ohio isolate in the choice test were similar to their responses in nonchoice tests. PI 200538 and PI 567597C were resistant to both the Ohio and Illinois isolates and will be useful sources of resistance to both isolates. These tests confirm that there are at least two distinct biotypes of A. glycines in North America.
  
  
  
• 2008: Twizeyimana, M., Ojiambo, P. S., Ikotun, T., Ladipo, J. L., Hartman, G. L., and Bandyopadhyay, R. 2008. Evaluation of soybean germplasm for resistance to soybean rust (Phakopsora pachyrhizi) in Nigeria. Plant Disease 92:947-952. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is one of the most important constraints to soybean production worldwide. The absence of high levels of host resistance to the pathogen has necessitated the continued search and identification of sources of resistance. In one set of experiments, 178 soybean breeding lines from the International Institute of Tropical Agriculture were rated for rust severity in the field in 2002 and 2003 at Ile-Ife, Yandev, and Ibadan, Nigeria. Thirty-six lines with disease severity ≤3 (based on a 0-to-5 scale) were selected for a second round of evaluation in 2004 at Ibadan. In the third round of evaluation under inoculated field conditions, 11 breeding lines with disease severity ≤2 were further evaluated for rust resistance at Ibadan in 2005 and 2006. The breeding lines TGx 1835-10E, TGx 1895-50F, and TGx 1903-3F consistently had the lowest level of disease severity across years and locations. In another set of experiments, 101 accessions from the United States Department of Agriculture–Agricultural Research Service and National Agriculture Research Organization (Uganda) were evaluated in the first round in 2005 under inoculated conditions in the screenhouse; 12 accessions with disease severity ≤20% leaf area infected were selected for evaluation in the second round in 2005 and 2006 under inoculated field conditions at Ibadan. Highly significant differences (P < 0.0001 in disease severity were observed among the 101 accessions during this first round of rust evaluation. Significant (P < 0.0001) differences in rust severity and sporulation also were observed among the 12 selected accessions. Accessions PI 594538A, PI 417089A, and UG-5 had significantly (P < 0.05) lower disease severity than all other selected accessions in both years of evaluation, with rust severities ranging from 0.1 to 2.4%. These results indicate that some of the breeding lines (TGx 1835-10E, TGx 1895-50F, and TGx 1903-3F) and accessions (PI 594538A, PI 417089A, and UG-5) would be useful sources of soybean rust resistance genes for incorporation into high-yielding and adapted cultivars.
  
  
  
• 2008: Vuong, T., Diers, B. W., and Hartman, G. L. 2008. Identification of QTL for resistance to Sclerotinia stem rot (Sclerotinia sclerotiorum) in plant introduction 194639. Crop Science 48:2209–2214. [download] [view abstract]
  Sclerotinia stem rot of soybean [Glycine max (L.) Merr.], caused by Sclerotinia sclerotiorum (Lib.) de Bary, is a diffi cult disease to manage, although some gains have been made through breeding for quantitative resistance. The objective of the present study was to map quantitative trait loci (QTL) controlling partial resistance to Sclerotinia stem rot from the soybean plant introduction (PI) 194639. The resistance QTL were mapped in a population of 155 F_4:5 recombinant inbred lines (RILs) developed from the hybridization of the partially resistant parent, PI 194639, to the susceptible cultivar Merit. The population was evaluated for Sclerotinia stem rot resistance using a cut stem inoculation technique and was genotyped with 134 simple sequence repeat (SSR) markers. Broad-sense heritability of lesion length (LL) after inoculation with the cut stem technique in the population was 0.57. Two putative QTL-controlling LL were identified by composite interval mapping (CIM) and mapped to linkage groups (LGs) A2 and B2, with likelihood of odds scores of 5.6 and 3.5, respectively. The LG A2 QTL was linked to the marker Sat_138 and explained 12.1% of the phenotypic variation for LL. The LG B2 QTL was proximal to the marker Satt126 and explained 11.2% of the phenotypic variance. Two minor QTL also were mapped onto LGs K and L, explaining 5.5% of the total phenotypic variation. A multivariate model that included all significant QTL explained 27% of the observed phenotypic variation of LL. These results suggest that SSR markers associated with resistance QTL mapped in this study for Sclerotinia stem rot resistance may be useful for marker-assisted breeding programs in soybean.
  
  
  
• 2008: Li, Y., Zou, J., Li, M., Bilgin, D. D., Vodkin, L. O., Hartman, G. L., and Clough, S. J. 2008. Soybean defense responses to the soybean aphid. New Phytologist 179: 185–195. [download] [view abstract]
  Transcript profiles in aphid (Aphis glycines)-resistant (cv. Dowling) and -susceptible (cv. Williams 82) soybean (Glycine max) cultivars using soybean cDNA microarrays were investigated. Large-scale soybean cDNA microarrays representing approx. 18 000 genes or c. 30% of the soybean genome were compared at 6 and 12 h post-application of aphids. In a separate experiment utilizing clip cages, expression of three defense-related genes were examined at 6, 12, 24, 48, and 72 h in both cultivars by quantitative real-time PCR. One hundred and forty genes showed specific responses for resistance; these included genes related to cell wall, defense, DNA/RNA, secondary metabolism, signaling and other processes. When an extended time period of sampling was investigated, earlier and greater induction of three defense-related genes was observed in the resistant cultivar; however, the induction declined after 24 or 48 h in the resistant cultivar but continued to increase in the susceptible cultivar after 24 h. Aphid-challenged resistant plants showed rapid differential gene expression patterns similar to the incompatible response induced by avirulent Pseudomonas syringae. Five genes were identified as differentially expressed between the two genotypes in the absence of aphids.
  
  
  
• 2008: Miles, M. R., Morel, W., Ray, J. D., Smith, J. R., Frederick, R. D., and Hartman, G. L. 2008. Adult plant evaluation of soybean accessions for resistance to Phakopsora pachyrhizi in the field and greenhouse in Paraguay. Plant Disease 92:96-102. [download] [view abstract]
  Five hundred thirty soybean accessions from maturity groups (MG) III through IX were evaluated for resistance to Phakopsora pachyrhizi in a replicated field trial at Centro Regional de Investigación Agrícola in Capitán Miranda, Itapúa, Paraguay during the 2005–06 season. Soybean rust severities of individual accessions ranged from 0% (resistant) to 30.0% (susceptible). In MG III and IV, the most resistant accessions were PI 506863, PI 567341, and PI 567351B, with severities less than 1.2%. In MG V, the most resistant accessions were PI 181456, PI 398288, PI 404134B, and PI 507305, with severities less than 0.3%. In MG VI, the most resistant accessions were PI 587886, PI 587880A, and PI 587880B, with severities less than 0.3%. In MG VII and VIII, the most resistant were PI 587905 and PI 605779E, with severities less than 1.0%. In MG IX, the most resistant accessions were PI 594754, PI 605833, PI 576102B, and PI 567104B, with severities less than 1.0%. The resistance in 10 selected accessions from MG VI, VII, VIII, and XI was confirmed in subsequent greenhouse and field experiments where severities of 0.4% or less and reddish-brown lesions with sporulation levels less than 3.0 were observed. These accessions, with low severities in the adult plant field evaluation, may be new sources of resistance to P. pachyrhizi.
  
  
  
• 2008: Slaminko, T. L., Miles, M. R., Frederick, R. D., Bonde, M. R., and Hartman, G. L. 2008. New legume hosts of Phakopsora pachyrhizi based on greenhouse evaluations. Plant Disease 92:767-771. [download] [view abstract]
  Phakopsora pachyrhizi, the causal organism of soybean rust, was first found in the continental United States in 2004 and has been found on soybean, kudzu, Florida beggarweed, and three Phaseolus species in the field. The pathogen has been reported to occur on more than 90 legume species worldwide and it is likely to infect native and introduced legume species in the United States. The objective of this study was to determine if 176 species representing 57 genera of legumes, the majority of which are either native or naturalized to soybean-growing areas of the United States, could be hosts of P. pachyrhizi. Between one and three accessions of each species, a total of 264 accessions, were inoculated with a mixture of four isolates of P. pachyrhizi. Severity and sporulation were rated on a 1-to-5 scale at 14 and 28 days after inoculation. P. pachyrhizi was confirmed by the presence of sporulating uredinia and/or immunological assay on 65 new species in 25 genera; 12 of these genera have not been reported previously as hosts. Many of the newly identified hosts grow in the southern United States, and like kudzu, could serve as overwintering hosts for P. pachyrhizi.
  
  
  
• 2008: Li, S., Lygin, A. V., Zernova, O. V., Lozovaya, V. V., Hartman, G. L., and Widholm, J. M. 2008. Genotype response of soybean (Glycine max) whole plants and hairy roots to Fusarium solani f. sp. glycines infection. Soybean Science 27:275-282. [download] [view abstract]
  Fusarium solani f. sp. glycines, a soilborne fungus, infects soybean roots and causes sudden death syndrome. The response of 13 soybean genotypes to F. solani f. sp. glycines infection was tested with potted greenhouse grown plants and with cultured hairy roots. The taproots of all genotypes grown in the greenhouse had dark brown lesions following inoculation. Foliar disease severity for greenhouse grown plants measured 21 days after planting was greatest for Peking, followed by Spencer, Ripley, P3981, Williams 82, Essex, Forrest, Iroquois, PI 520733, Hartwig, PI 567650B, Jack, and PI 567374. There were significant negative correlations between foliar disease severity and shoot length (r = -0.422, P = 0.0018), shoot weight (r = -0.857, P < 0.0001), root weight (r = -0.732, P <0.0001), and total plant dry weights (r = -0.855, P < 0.0001). The taproot lesion length was not correlated with foliar disease severity indicating that soybean resistance may not be fully controlled at the root level. When cultured hairy roots were inoculated with F. solani f. sp. glycines mycelial plugs, the colony diameters after 10 days were significantly (P = 0.05) different among soybean genotypes ranging from 17 to 40 mm. Fungal colony diameters on hairy roots of Spencer and Peking were greater (P = 0.05) than on PI 567374 and PI 520733. In another experiment, following inoculation of Spencer and PI 567374 hairy roots with 10 µL of F. solani f. sp. glycines macroconidial suspensions, 10-day-colony diameters were 50 and 38 mm, respectively (P = 0.05). While there was generally a correlation between the growth of F. solani f. sp. glycines on the cultured hairy roots and the whole plant symptoms of the different genotypes, this was not always the case. The exceptions may be due to the fact that none of the genotypes showed clear root resistance even though they may show toxin resistance that would result in fewer foliar symptoms.
  
  
  
• 2007: Mueller, T. A., Miles, M. R., Hartman, G. L., Levy, C. 2007. Evaluation of fungicides and fungicide timing for the control of soybean rust in Zimbabwe, 2005-2006. Plant Disease Management Reports 1:FC103. [link]
  
  
• 2007: Mueller, T. A., Miles, M. R., Hartman, G. L., Morel, W. 2007. Evaluation of fungicides and fungicide timing for the control of soybean rust at Pirapo, Paraguay, 2005-2006. Plant Disease Management Reports 1:FC063. [link]
  
  
• 2007: Mueller, T. A., Miles, M. R., Hartman, G. L., Morel, W. 2007. Evaluation of fungicides and fungicide timing for the control of soybean rust at Capitán Meza, Paraguay, 2006. Plant Disease Management Reports 1:FC062. [link]
  
  
• 2007: Mueller, T. A., Miles, M. R., Hartman, G. L., Morel, W. 2007. Evaluation of fungicides and fungicide timing for the control of soybean rust at Bella Vista, Paraguay, 2005-2006. Plant Disease Management Reports 1:FC104. [link]
  
  
• 2007: Farias Neto, A. L. de, Hashmi, R., Schmidt, M., Carlson, S. R., Hartman, G. L., Li, S., Nelson, R. L., and Diers, B. W. 2007. Mapping and confirmation of a new sudden death syndrome resistance QTL on linkage group D2 from the soybean genotypes PI 567374 and 'Ripley'. Molecular Breeding 20:53-62. [link]
  
  
• 2007: Li, Y., Hill, C. B., Carlson, S. R., Diers, B. W., and Hartman, G. L. 2007. Soybean aphid resistance genes in the soybean cultivars Dowling and Jackson map to linkage group M. Molecular Breeding 19: 25-34. [link]
  
  
• 2007: Thekkeveetil, T., Hobbs, H. A., Wang, Y., Kridelbaugh, D., Donnelly, J., Hartman, G. L., and Domier, L. L. 2007. First report of Soybean dwarf virus in soybean in northern Illinois. Plant Disease 91:1686. [download]
  
  
• 2007: Ojiambo, P. S., Bandyopadhyay, R., Twizeyimana, M., Lema, A., Frederick, R. D., Pedley, K. F., Stone, C. L., and Hartman, G. L. 2007. First report of rust caused by Phakopsora pachyrhizi on soybean in Democratic Republic of Congo. Plant Disease 91:1204. [download] [view abstract]
  Nigeria and Uganda are the closest countries to the Democratic Republic of Congo (DRC) where soybean rust caused by Phakopsora pachyrhizi has been reported. In February 2007, during a disease survey in DRC, soybean (Glycine max) leaves with rust symptoms (tan, angular lesions with erumpent sori exuding urediniospores) were observed in 10 fields in the following areas in Bas Congo Province: Bangu, Kimpese, Kolo-Fuma, Lukala, Mbanza-Ngungu, Mpalukide, Mvuazi, and Ntemo. Rust incidence in these fields ranged from 85 to 100%, while severity ranged between 3 and 35% of the leaf area on infected plants. Urediniospores were hyaline, minutely echinulate, and 23 to 31 × 16 to 20 µm. Within a week of collection, infected leaf samples were sent to the USDA-ARS Foreign Disease-Weed Science Research Unit (FDWSRU) for pathogen identification. DNA was extracted from sections of leaves containing sori with the Qiagen DNeasy Plant Mini kit (Valencia, CA), and all 10 field samples amplified in a real-time fluorescent PCR with the P. pachyrhizi-specific primers Ppm1 and Ppa2. Infected leaves of cultivar Vuangi collected from one field each in the INERA Research Station, Kimpese-Crawford, and Kimpese-Ceco were separately washed in sterile water to collect urediniospores that were used to separately inoculate three detached leaves of susceptible cultivar TGx 1485-1D. Lesions on inoculated leaves developed 5 days after inoculation (DAI), and pustules (110 to 130 µm) formed 7 DAI and erupted 2 days later exuding columns of urediniospores similar in size to the initially collected isolates. Inoculation of another set of detached leaves with a spore suspension (1 × 10(^6) spores per ml) from the first set of detached leaves resulted in typical rust symptoms. Seedlings of cultivar Williams also showed typical rust symptoms when inoculated separately with urediniospores collected from nine fields (i.e., all except Kimpese-Ceco, which was infective in the detached leaf assay). Inoculation and incubation were carried out at the FDWSRU Plant Pathogen Containment Facility at Fort Detrick as described earlier (2). The PCR assay, morphological characters of the isolates, and pathogenicity tests demonstrate that P. pachyrhizi occurs in DRC. To our knowledge, this is the first report of P. pachyrhizi infecting soybean in DRC.
  
  
  
• 2007: Hyten, D. L., Hartman, G. L., Nelson, R. L., Frederick, R. D., Concibido, V. C., and Cregan, P. B. 2007. Map location of the Rpp1 locus that confers resistance to Phakopsora pachyrhizi(soybean rust) in soybean. Crop Science 47:837-838. [download] [view abstract]
  Soybean rust (SBR), caused by Phakopsora pachyrhizi, was first discovered in North America in 2004 and has the potential to become a major soybean [Glycine max (L.) Merr.] disease in the USA. Currently, four SBR resistance genes have been identified but not mapped on the soybean genetic linkage map. One of these resistance genes is the Rpp1 gene, which is present in the soybean accession PI 200492. The availability of molecular markers associated with Rpp1 will permit marker-assisted selection and expedite the incorporation of this gene into U.S. cultivars. We compared simple sequence repeat (SSR) markers between ‘Williams 82’ and the BC5 Williams 82 isoline L85-2378, which contains the Rpp1 resistance allele from the soybean accession PI 200492, for candidate regions that might contain Rpp1. One candidate region was found with the SSR marker BARC_Sct_187 on linkage group G. A population of BC6F_2:3 lines segregating for the Rpp1 resistance locus was genotyped in this region on linkage group G followed by inoculation with the P. pachyrhizi isolate India 73-1 in the USDA-ARS Biosafety Level 3 Plant Pathogen Containment Facility at Ft. Detrick, MD. The Rpp1 gene was mapped between SSR markers BARC_Sct_187 and BARC_Sat_064 on linkage group G.
  
  
  
• 2007: Lim, H. S., Ko, T. S., Hobbs, H. A., Lambert, K. N., Yu, J. M., McCoppin, N. K., Korban, S. S., Hartman, G. L., and Domier, L. L. 2007. Soybean mosaic virus helper component-protease alters leaf morphology and reduces seed production in transgenic soybean plants. Phytopathology 9:366-372. [download] [view abstract]
  Transgenic soybean (Glycine max) plants expressing Soybean mosaic virus (SMV) helper component-protease (HC-Pro) showed altered vegetative and reproductive phenotypes and responses to SMV infection. When inoculated with SMV, transgenic plants expressing the lowest level of HC-Pro mRNA and those transformed with the vector alone initially showed mild SMV symptoms. Plants that accumulated the highest level of SMV HC-Pro mRNA showed very severe SMV symptoms initially, but after 2 weeks symptoms disappeared, and SMV titers were greatly reduced. Analysis of SMV RNA abundance over time with region-specific probes showed that the HC-Pro region of the SMV genome was degraded before the coat protein region. Transgenic soybean plants that expressed SMV HC-Pro showed dose-dependent alterations in unifoliate leaf morphologies and seed production where plants expressing the highest levels of HC-Pro had the most deformed leaves and the lowest seed production. Accumulation of microRNAs (miRNAs) and mRNAs putatively targeted by miRNAs was analyzed in leaves and flowers of healthy, HC-Pro-transgenic, and SMV-infected plants. Neither expression of SMV HC-Pro nor SMV infection produced greater than twofold changes in accumulation of six miRNAs. In contrast, SMV infection was associated with twofold or greater increases in the accumulation of four of seven miRNA-targeted mRNAs tested.
  
  
  
• 2007: Daniel, S. L., Hartman, G. L., Wagner, E. D., and Plewa, M. J. 2007. Mammalian cell cytotoxicity analysis of soybean rust fungicides. Bulletin Environmental Contamination Toxicology 78:474-478. [download]
  
  
• 2007: Twizeyimana, M., Ojiambo, P. S., Ikotun, T., Paul, C., Hartman, G. L., and Bandyopadhyay, R. 2007. Comparison of field, greenhouse, and detached leaf evaluations of soybean germplasm for resistance to Phakopsora pachyrhizi. Plant Disease 91:1161-1169. [download] [view abstract]
  Fourteen soybean accessions and breeding lines were evaluated for resistance to soybean rust caused by the fungus Phakopsora pachyrhizi. Evaluations were conducted in replicated experiments in growth chambers using detached leaves and under greenhouse and field conditions. In growth-chamber experiments, inoculation of detached leaves with 1 × 106 spores/ml resulted in a significantly (P < 0.0001) higher total number of pustules and spores per unit leaf area than inoculations with lower spore concentrations. Amending agar medium with plant hormones significantly (P < 0.0001) aided retention of green leaf color in detached leaves. Leaf pieces on a medium containing kinetin at 10 mg/liter had 5% chlorosis at 18 days after plating compared with leaf pieces on media amended with all other plant hormones, which had higher levels of chlorosis. Leaf age significantly affected number of pustules (P = 0.0146) and number of spores per pustule (P = 0.0088), and 3- to 4-week-old leaves had a higher number of pustules and number of spores per pustule compared with leaves that were either 1 to 2 or 5 to 6 weeks old. In detached-leaf and greenhouse screening, plants were evaluated for days to lesion appearance, days to pustule formation, days to pustule eruption, lesion number, lesion diameter, lesion type, number of pustules, and spores per pustule in 1-cm2 leaf area. Plants also were evaluated for diseased leaf area (in greenhouse and field screening) and sporulation (in field screening) at growth stage R6. There were significant (P < 0.0001) differences among genotypes in their response to P. pachyrhizi infection in the detached-leaf, greenhouse, and field evaluations. Accessions PI 594538A, PI 417089A, and UG-5 had very low levels of disease compared with the susceptible checks and all other genotypes. Detached-leaf, greenhouse, and field results were comparable, and there were significant correlations between detached-leaf and greenhouse (absolute r = 0.79; P < 0.0001) and between detached-leaf and field resistance (absolute r = 0.83; P< 0.0001) across genotypes. The overall results show the utility of detached-leaf assay for screening soybean for rust resistance.
  
  
  
• 2007: Hartman, G. L., Hines, R. A., Faulkner, C. D., Lynch, T. N., and Pataky, N. 2007. Late season occurrence of soybean rust caused by Phakopsora pachyrhizi on soybean in Illinois. Plant Disease 91:466. [download]
  
  
• 2007: Bandyopadhyay, R., Ojiambo, P. S., Twizeyimana, M., Asafo-Adjei, B., Frederick, R. D., Pedley, K. F., Stone, C. L., and Hartman, G. L. 2007. First report of soybean rust caused by Phakopsora pachyrhizi in Ghana. Plant Disease 91:1057. [download]
  
  
• 2007: Patzoldt, M. E., Tyagi, R. K., Hymowitz, T., Miles, M. R., Hartman G. L. and Frederick, R. D. 2007. Soybean rust resistance derived from Glycine tomentella in amphiploid hybrid lines. Crop Sci. 47: 158-161. [download] [view abstract]
  Soybean rust (SBR), caused by the fungal pathogen Phakopsora pachyrhizi Syd., has the potential to cause significant economic yield loss in U.S. soybean production. Four single dominant resistance genes have been identified in soybean [Glycine max (L.) Merr.] that only confer specific resistance to a few rust isolates that have been tested. Additional resistance genes have been identified in wild perennial relatives, including G. tomentella Hayata (accession PI 483218, 2n = 78). Intersubgeneric hybrids have been created between G. max (cv. Altona) and this G. tomentella accession. Amphiploid hybrid lines (2n = 118) were the result of this hybridization and when further backcrossed to G. max (cv. Clark 63), derived fertile lines (2n = 40) were also generated. Both sets of progeny were screened at the USDA-ARS facility at Ft. Detrick, MD, to determine if the resistance to SBR was inherited in the subsequent populations. The amphiploid hybrid clones still retained the genetic SBR resistance that was found in the G. tomentella parent. However, the derived fertile lines were susceptible. These lines were not screened for SBR resistance following each backcross, which may explain this occurrence. Reinstituting the backcross procedure, while testing for SBR resistance at every generation, could move the SBR resistance gene(s) from G. tomentella to the cultivated soybean G. max.
  
  
  
• 2007: Miles, M. R., Pastor-Corrales, M. A., Hartman, G. L., and Frederick, R. D. 2007. Differential response of common bean cultivars to Phakopsora pachyrhizi. Plant Disease 91:698-704. [download] [view abstract]
  Soybean rust (Phakopsora pachyrhizi) has been reported on common bean (Phaseolus vulgaris) in Asia, South Africa, and the United States. However, there is little information on the interaction of individual isolates of Phakopsora pachyrhizi with common bean germplasm. A set of 16 common bean cultivars with known genes for resistance to Uromyces appendiculatus, the causal agent of common bean rust, three soybean accessions that were sources of the single gene resistance to P. pachyrhizi, and the moderately susceptible soybean ‘Ina’ were evaluated using seedlings inoculated with six isolates of P. pachyrhizi. Among the common bean cultivars, Aurora, Compuesto Negro Chimaltenango, and Pinto 114, were the most resistant to all six P. pachyrhizi isolates, with lower severity, less sporulation, and consistent reddish-brown (RB) lesions associated with resistance in soybean. A differential response was observed among the common bean cultivars, with a cultivar-isolate interaction for both severity and sporulation levels, as well as the presence or absence of the RB lesion type. This differential response was independent of the known genes that condition resistance to U. appendiculatus, suggesting that resistance to P. pachyrhizi was independent of resistance to U. appendiculatus.
  
  
  
• 2007: Miles, M. R., Levy, C., Morel, W., Mueller, T. A., Steinlage, T., van Rij, N. C., Frederick, R. D., and Hartman, G. L. 2007. International fungicide efficacy trials for the management of soybean rust. Plant Disease 91:1450-1458. [download] [view abstract]
  The efficacy of fungicides in managing soybean rust was evaluated in 12 environments in South America and southern Africa over three growing seasons from 2002 to 2005. There were differences in final soybean rust severity, defoliation, and yield among the treatments at most locations. In locations where soybean rust was not severe, all the fungicides evaluated reduced severity. In locations where soybean rust was severe, applications of triazole and triazole + strobilurin fungicides resulted in lower severity and higher yields compared with other fungicides. The strobilurin fungicides provided the highest yields in many locations; however, severity tended to be higher than that of the triazole fungicides. There also were differences in yield and severity between the trials with two and three applications of several fungicides, with three applications resulting in less severe soybean rust and higher yields. However, the third application of tebuconazole, tetraconazole, and the mixtures containing azoxystrobin and pyraclostrobin was not needed to maintain yield. These fungicides were among the most effective for managing soybean rust and maintaining yield over most locations.
  
  
  
• 2007: Domier, L. L., Steinlage, T. A., Hobbs, H. A., Yang, Y., Herrera-Rodriguez, G., Haudenshield, J. S., McCoppin, N. K., and Hartman, G. L. 2007. Similarities in seed and aphid transmission among Soybean mosaic virus isolates. Plant Disease 91: 546-550. [download] [view abstract]
  Soybean mosaic virus (SMV) is an aphid- and seed-transmitted virus that infects soybean (Glycine max) plants and causes significant yield losses. Seed-borne infections are the primary sources of inoculum for SMV infections. The strain specificity of SMV transmission through seed and SMV-induced seed-coat mottling were investigated in field experiments. Six soybean plant introductions (PIs) were inoculated with eight SMV strains and isolates. Transmission of SMV through seed ranged from 0 to 43%, and isolate-by-soybean line interactions occurred in both transmission rates and percentages of mottled seeds. For example, SMV 746 was transmitted through 43% of seed in PI 229324, but was not transmitted through seed of PIs 68522, 68671, or 86449. In contrast, SMV 413 was transmitted through seed from all PIs. SMVs that were transmitted poorly by the Asian soybean aphid, Aphis glycines, also were transmitted poorly through seed. No predicted amino acid sequences within the helper-component protease or coat protein coding regions differentiated the two groups of SMV strains. The loss of aphid and seed transmissibility by repeated mechanical transmission suggests that constant selection pressure is needed to maintain the regions of the SMV genome controlling the two phenotypes from genetic drift and loss of function.
  
  
  
• 2006: Farias Neto, A. L. de, Hartman, G. L., Pedersen, W. L., Li, S., Bollero, G. A., and Diers, B. W. 2006. Irrigation and inoculation treatments that increase the severity of soybean sudden death syndrome in the field. Crop Science 46:2547-2554. [link] [view abstract]
  The occurrence of sudden death syndrome (SDS), caused by the fungus Fusarium solani (Mart.) Sacc. f. sp. glycines (FSG) (syn. Fusarium virguliforme Akoi, O’Donnell, Homma and Lattanzi), is unpredictable in soybean [Glycine max (L.) Merr.] field trials making it difficult to evaluate soybean for resistance to the pathogen. Our objective was to evaluate the effect of field inoculation, soil compaction, and irrigation on the occurrence and severity of SDS symptoms. Six inoculation treatments were tested which included applications of FSG-infested grain planted in the furrow with the soybean seed, broadcasted and incorporated into the soil before planting, or placed below the soybean seed just before planting. Soil was compacted by driving a tractor across the field once in early spring. Irrigation treatments were applied at combinations of growth stages V3, V7, R3, R4, and/or R5. Significant increases in foliar SDS severity were observed from inoculation and irrigation treatments (P , 0.05), but not from compaction treatments. The inoculation treatments that placed inoculum close to the seed resulted in the greatest foliar severity. Irrigation treatments during mid to late reproductive growth stages resulted in significant increases in SDS foliar symptom development. These results increase our understanding of what environmental conditions increase SDS field symptoms and will be useful to researchers establishing SDS field nurseries.
  
  
  
• 2006: Lozovaya, V. V., Lygin, A. V., Zernova, O. V., Ulanov, A. V., Li, S., Hartman, G. L., and Widholm, J. M. 2006. Modification of phenolic metabolism in soybean hairy roots through down regulation of chalcone synthase or isoflavone synthase. Planta 225:665-679. [link] [view abstract]
  Soybean hairy roots, transformed with the soybean chalcone synthase (CHS6) or isoflavone synthase (IFS2) genes, with dramatically decreased capacity to synthesize isoflavones were produced to determine what effects these changes would have on susceptibility to a fungal pathogen. The isoflavone and coumestrol concentrations were decreased by about 90% in most lines apparently due to gene silencing. The IFS2 transformed lines had very low IFS enzyme activity in microsomal fractions as measured by the conversion of naringenin to genistein. The CHS6 lines with decreased isoflavone concentrations had 5 to 20-fold lower CHS enzyme activities than the appropriate controls. Both IFS2 and CHS transformed lines accumulated higher concentrations of both soluble and cell wall bound phenolic acids compared to controls with higher levels found in the CHS6 lines indicating alterations in the lignin biosynthetic branch of the pathway. Induction of the soybean phytoalexin glyceollin, of which the precursor is the isoflavone daidzein, by the fungal pathogen Fusarium solani f. sp. glycines (FSG) that causes soybean sudden death syndrome (SDS) showed that the low isoflavone transformed lines did not accumulate glyceollin while the control lines did. The (iso)liquritigenin content increased upon FSG induction in the IFS2 transformed roots indicating that the pathway reactions before this point can control isoflavonoid synthesis. The lowest fungal growth rate on hairy roots was found on the FSG partially resistant control roots followed by the SDS sensitive control roots and the low isoflavone transformants. The results indicate the importance of phytoalexin synthesis in root resistance to the pathogen.
  
  
  
• 2006: Miles, M. R., Hartman, G. L., and Levy, C. 2006. Control of soybean rust in an indeterminate cultivar at the Gwebi Variety Testing Center, Zimbabwe, 2004-05. F&N Tests 61:FC004. [download]
  
  
• 2006: Miles, M. R., Hartman, G. L., van Rij, N. C., Tweer, S., du Preez, E. D., and Lawrance, K. F. 2006. Evaluations of fungicides for control of soybean rust in the cultivar 'Prima 2000' near Cedara, South Africa, 2004-05. F&N Tests 61:FC002. [download]
  
  
• 2006: Bent, A.F., T.K. Hoffman, J.C. Schmidt, G.L. Hartman, D.D. Hoffman, P. Xue, and M.L. Tucker. 2006. Disease- and performance-related traits of ethylene-insensitive soybean. Crop Science 46:893-901. [download] [view abstract]
  Ethylene controls many beneficial responses in plants but also promotes chlorosis, senescence, disease, and fruit over-ripening. The present study compared previously isolated ethylene-insensitive lines of soybean [Glycine max (L.) Merr.] to their isogenic, ethylene-sensitive parent with respect to disease resistance, seed yield, and other field performance traits. In laboratory tests, ethylene insensitivity reduced root colonization by soybean cyst nematode. Using healthy young plants, ethylene-insensitivity also reduced ethylene-activated leaf chlorosis and abscission. However, in the field, leaf chlorophyll and late-season senescence were not altered, suggesting that ethylene is not a main determinant of late-season senescence of soybean leaves. Field studies also revealed no changes in susceptibility to Septoria brown spot disease (caused by Septoria glycines Hemmi), flowering date, plant height, or seed total protein and oil concentration. Field studies did demonstrate elevated susceptibility to white mold disease [Sclerotinia sclerotiorum (Lib.) deBary], poor stand establishment in some but not all environments, altered plant architecture, and earlier maturity date in the ethylene-insensitive lines. Seed yield was notably undependable, being similar to the parental line in some field locations but significantly reduced in most environments. To avoid these negative impacts on overall performance, manipulation of plant ethylene responses should be targeted to specific tissues, growth stages, or growth environments.
  
  
  
• 2006: Diers, B. W., Kopisch-Obuch, F. J., Hoffman, D. D., Hartman, G. L., Pedersen, W. L., Grau, C. R., and Wang, D. 2006. Registration of AxN-1-55 soybean germplasm with partial resistance to Sclerotinia stem rot. Crop Science 46:1403-1404. [download] [view abstract]
  AxN-1-55 soybean [Glycine max (L.) Merr.] (Reg. no. GP-315, PI 640911) was developed by the Illinois Agricultural Experiment Station at the University of Illinois and the Michigan Agricultural Experiment Station at Michigan State University. AxN-1-55 was released in 2005 as a mid group II maturity germplasm line for use as a parent because of its high level of resistance to Sclerotinia stem rot [caused by Sclerotinia sclerotiorum (Lib.) de Bary].
  
  
  
• 2006: Hill, C. B., Li, Y., and Hartman, G. L. 2006. A single dominant gene for resistance to the soybean aphid in the soybean cultivar Dowling. Crop Science 46:1601-1605. [download] [view abstract]
  The soybean aphid (Aphis glycines Matsumura), a new pest of soybean [Glycine max (L.) Merr.], rapidly spread throughout North America after its arrival in 2000 and caused millions of dollars in economic losses. At present, the application of insecticides is the only means to control the soybean aphid. However, genetic resistance to the aphid was recently discovered in soybean germplasm and the soybean cultivar Dowling was identified as having strong antibiosis-type aphid resistance. The objective of this study was to determine the inheritance of resistance to the soybean aphid in Dowling. Resistance in F1, F2, and F2–derived F3 (F2:3) families from crosses between Dowling and the two susceptible soybean cultivars Loda and Williams 82 was analyzed. All F1 plants were resistant to the aphid. Heterogeneity of segregation of F2 plants in 14 Dowling x Loda F2 families was nonsignificant (P = 0.16), and pooled F2 data, with 132 resistant to 45 susceptible plants, fit a 3:1 ratio (P = 0.90). F2 plants from Dowling x Williams 82 segregated 135 resistant to 44 susceptible, also fitting a 3:1 ratio (P = 0.89). Segregation among the F2:3 families fit a 1:2:1 monogenic inheritance pattern. These results indicated that a single dominant gene named Rag1 controlled resistance in Dowling. The monogenic dominant nature of resistance will enable breeders to rapidly convert existing susceptible cultivars to resistant cultivars using backcrossing procedures.
  
  
  
• 2006: Harmon, C.L., P.F. Harmon, T.A. Mueller, J.J. Marois, and G.L. Hartman. 2006. First report of Phakopsora pachyrhizi telia on kudzu in the United States. Plant Disease 90:380. [download]
  
  
• 2006: Isard, S. A., Dufault, N. S., Miles, M. R., Hartman, G. L., Russo, J. M., De Wolf, E. D., and Morel, W. 2006. The effect of solar irradiance on the mortality of Phakopsora pachyrhizi urediniospores. Plant Dis 90:941-945. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, may be the most important foliar disease of soybean. Within the last 10 years, the fungus has moved to many new geographical locations via spread of airborne urediniospores. The objective of this study was to determine the relationship between urediniospore viability and exposure to solar radiation. Urediniospores of P. pachyrhizi were exposed in Capitán Miranda, Paraguay, to determine the deleterious effects of sunlight. Concomitant total solar (0.285 to 2.8 µm) and ultraviolet (0.295 to 0.385 µm) irradiance measurements were used to predict urediniospore germination. Urediniospores exposed to doses of solar and ultraviolet (UV) radiation ≥27.3 MJ/m2 and ≥1.2 MJ/m2, respectively, did not germinate. The proportions of urediniospores that germinated, normalized with respect to the germination proportion for unexposed urediniospores from the same collections, were a linear function of solar irradiance (R2 = 0.83). UV measurements predicted normalized germination proportions equally well. Results of inoculation experiments with exposed P. pachyrhizi urediniospores supported the results of the germination trials, although the effects of moderate levels of irradiance varied. The relationship between urediniospore viability and exposure to solar radiation has been incorporated into the U.S. Department of Agriculture’s soybean rust aerobiological model that provides North American soybean growers with decision support for managing soybean rust.
  
  
  
• 2006: Hill, C. B., Hartman, G. L., Esgar, R., and Hobbs, H. A. 2006. Field evaluation of green stem disorder in soybean cultivars. Crop Science 46:879-885. [download] [view abstract]
  Green stem is a disorder of soybean [Glycine max (L.) Merrill] that causes the stems to remain green, nonsenescent, and moist, although pods and seeds are fully ripe and dry. The disorder is a nuisance for producers because it complicates harvesting of soybeans by significantly increasing the difficulty in cutting the affected plants during harvest. The cause of the disorder is unknown; however, differences in relative sensitivity to the disorder have been observed. The primary objective of this research was to evaluate the relative sensitivity among commercial or near-commercial cultivars from private and public soybean breeding organizations in replicated variety tests in Illinois. In 31 tests at Dekalb, Monmouth, and Urbana, IL, during 2001 to 2004, 1187 different MG I (maturity group)-MG IV conventional and glyphosate[N-(phosphonomethyl)glycine]-tolerant, cultivars were visually evaluated. There were significant differences in sensitivity among cultivars in 29 of the 31 tests, indicating that genetic variability among cultivars for green stem sensitivity exists. This variability may provide a basis for breeding for low sensitivity to the green stem disorder. Total levels of green stem disorder incidence varied over years and locations. Herbicide management systems did not appear to affect the levels of green stem incidence.
  
  
  
• 2006: Miles, M. R., Hartman, G. L., and Levy, C. 2006. Control of soybean rust in a determinate cultivar at the Rattray Arnold Research Station, Zimbabwe, 2004-05. F&N Tests 61:FC003. [download]
  
  
• 2006: Mueller, T. A., Miles, M. R., Hartman, G. L., and Morel, W. 2006. Evaluations of fungicides for the control of soybean rust at Bella Vista, Paraguay, 2004-2005. F&N Tests 61:FC007. [download]
  
  
• 2006: Bonde, M. R., S. E. Nester, C. N. Austin, C. L. Stone, R. D. Frederick, G. L. Hartman, and M. R. Miles. 2006. Evaluation of virulence of Phakopsora pachyrhizi and P. meibomiae isolates. Plant Disease 90:708-716. [download] [view abstract]
  Asian soybean rust (ASR), caused by Phakopsora pachyrhizi and recently discovered for the first time in continental United States, has been of concern to the U.S. agricultural industry for more than 30 years. Since little soybean rust resistance is known, and resistance is often difficult to detect or quantitate, we initiated a project to develop a better, more quantitative, method. The methodology determined the average numbers and diameters of uredinia in lesions that developed on leaves of inoculated plants 14 days after inoculation. It was used to compare virulence of P. pachyrhizi isolates from Asia and Australia and P. meibomiae from Puerto Rico and Brazil, collected as many as 30 years earlier, with isolates of P. pachyrhizi recently collected from Africa or South America. Susceptible reactions to P. pachyrhizi resulted in tan-colored lesions containing 1 to 14 uredinia varying greatly in size within individual lesions. In contrast, on these same genotypes at the same time of year, resistance to other P. pachyrhizi isolates was typified by 0 to 6 small uredinia in reddish-brown to dark-brown lesions. Using appropriate rust resistant and rust susceptible genotypes as standards, examination of uredinia 14 days after inoculation allowed quantitative comparisons of sporulation capacities, one measure of susceptibility or resistance to soybean rust. The study verified the presence and ability to detect all known major genes for resistance to soybean rust in the original sources of resistance. It demonstrated that soybean lines derived from the original PI sources, and presumed to possess the resistance genes, in actuality may lack the gene or express an intermediate reaction to the rust pathogen. We suggest that a determination of numbers and sizes of uredinia will detect both major gene and partial resistance to soybean rust.
  
  
  
• 2006: Gao, X., Jackson, T. A., Hartman, G. L., and Niblack, T. L. 2006. Interactions between soybean cyst nematode and Fusarium solani f. sp. glycines based on greenhouse factorial experiments. Phytopathology 96:1409-1415. [download] [view abstract]
  Soybean cyst nematode, Heterodera glycines, and the fungus that causes sudden death syndrome of soybean (SDS), Fusarium solani f. sp. glycines, frequently co-infest soybean (Glycine max) fields. The interactions between H. glycines and F. solani f. sp. glycines were investigated in factorial greenhouse experiments with different inoculum levels of both organisms on a soybean cultivar susceptible to both pathogens. Responses measured included root and shoot fresh and dry weights, H. glycines reproduction, area under the SDS progress curve (AUDPC), and fungal colonization. Results of experimets conducted in two greenhouse environments were analyzed separately by 2-way, and 3-way analysis of variance (ANOVA) models that were developed that included the effect of greenhouse environment. Both H. glycines and F. solani f. sp. glycines affected the growth of soybeans in an additive pattern. Reproduction of H. glycines was suppressed (P=0.05) by high inoculum levels of F. solani f. sp. glycines, whereas the low the level had no significant impact. Real-time PCR assays were used to quantify fungal infection of soybean roots by F. solani f. sp. glycines and indicated that the infection of soybean roots by H. glycines did not impact colonization of F. solani f. sp. glycines.
  
  
  
• 2006: Miles, M. R., R. D. Frederick, and G. L. Hartman. 2006. Evaluation of soybean germplasm for resistance to Phakopsora pachyrhizi. Online. Plant Health Progress: doi 10.1094/PHP-2006-0104-01-RS. [download] [view abstract]
  The accessions in the USDA Germplasm Collection at the Univ. of Illinois were evaluated to identify soybean germplasm with resistance to soybean rust. The inoculation program used a mixture of four P. pachyrhizi isolates. Of 16,595 accessions rated for rust severity, 3,215 were selected for a second round of evaluation. Of these, 805 were selected for further evaluation. Some of these selected accessions have the potential to provide soybean rust resistance genes that may be useful for incorporation into commercial soybean cultivars.
  
  
  
• 2006: Hill, C. B., Li, Y., and Hartman, G. L. 2006. Soybean aphid resistance in soybean Jackson is controlled by a single dominant gene. Crop Science 46:1606-1608. [download] [view abstract]
  The soybean aphid, Aphis glycines Matsumura, has become established as a serious pest of soybean, Glycine max (L.) Merr., since it was first found in North America in 2000 and has caused millions of dollars in economic losses. While the application of chemical insecticides is the only means to control the soybean aphid at present, genetic resistance to the aphid was recently discovered in soybean. A single dominant gene named Rag1 that controls resistance to the soybean aphid was found in the cultivar Dowling. Another cultivar found to have strong antibiosis-type resistance to the soybean aphid was Jackson. The primary objective of this study was to determine the inheritance of resistance to the soybean aphid in Jackson. Segregation of resistance was analyzed in F2 and among F2–derived F3 (F2:3) families produced from crosses between Jackson and the susceptible soybean cultivar Loda. Segregation of F2 plants was 247 resistant to 97 susceptible and fit a 3:1 genetic ratio (P = 0.17). Segregation among F2:3 families was not clear because a number of susceptible F2 plants did not produce a sufficient amount of seed for progeny testing. Ignoring the susceptible class, the segregation of F2:3 families fit a 1:2 (all resistant/segregating) ratio. These results indicated that a single dominant gene controlled resistance in Jackson. There is no known genetic relationship between Jackson and Dowling. The genetic relationship between Rag1 in Dowling and the gene in Jackson is unknown.
  
  
  
• 2006: Lozovaya, V.V., A.V. Lygin, O.V. Zernova, S. Li, J. M. Widholm, and G. L. Hartman. 2006. Lignin degradation by Fusarium solani f. sp. glycines. Plant Disease 90:77-82. [download]
  
  
• 2006: Lynch, T. N., J. J. Marois, D. L. Wright, P.F. Harmon, M. R. Miles, and G. L. Hartman. 2006. First report of soybean rust caused by Phakopsora pachyrhizi on Phaseolus spp. in the United States. Plant Disease 90:970. [download] [view abstract]
  Phakopsora pachyrhizi Syd. & P. Syd., the cause of soybean rust, was first observed in the continental United States in November 2004 (2). During the growing season of 2005, P. pachyrhizi was confirmed on soybean (Glycine max) and/or kudzu (Pueraria montana) in nine states in the southern United States. It is known that P. pachyrhizi has a much larger host range within the Fabaceae family. On 29 September 2005 in Quincy, FL, 45 entries of mostly large-seeded legumes were planted next to soybeans that were infected with P. pachyrhizi. Several seeds of each entry were planted on one hill. Soybean plants growing adjacent to these potential hosts had 15 to 25% of the leaf area affected, 95% incidence, and 73% defoliation on 16 November. On 7 December 2005, all the plants of Phaseolus coccineus L. (scarlet runner bean, PI311827), Phaseolus lunatus L. (lima bean, PI583558), and two Phaseolus vulgaris L. (kidney bean) cvs. Red Hawk and California Early Light Red Kidney (CELRK) were found to have leaves with suspected rust lesions. These plants were at physiological maturity but had not senesced. None of the hosts had been inoculated other than from spores produced by the adjacent rust-infected soybean plants or from unknown locations. On the basis of microscopic examination, suspected infected leaves from plants of the Phaseolus spp. had rust pustules characteristic of P. pachyrhizi uredinia. Uredinia were counted within a randomly selected 2-cm(^2) area of one leaf of each sample. The mean and range of uredinia per lesion for Phaseolus coccineus was 29 uredinia with a range of 0 to 3 uredinia per lesion, Phaseolus lunatus had 2 uredinia with 0 to 1 uredinium per lesion, Phaseolus vulgaris cv. Red Hawk had 22 uredinia with 0 to 5 uredinia per lesion, and Phaseolus vulgaris cv. CELRK had 43 uredinia with 0 to 4 uredinia per lesion. Polymerase chain reactions using two sets of primers (Ppa1/Ppa2 and Pme1/Pme2) were performed on DNA extracted from leaves of the three species with sporulating rust pustules. The results of these tests and further tests conducted by the USDA/APHIS confirmed that P. pachyrhizi was the causal organism for the observed rust.
  
  
  
• 2006: Ferro, C.R., C.B. Hill, M.R. Miles, and G.L. Hartman. 2006. Evaluation of soybean cultivars with the Rps1k gene for partial resistance or field tolerance to Phytophthora sojae. Crop Science 46:2427-2436. [download] [view abstract]
  Phytophthora root rot, caused by Phytophthora sojae Kaufmann and Gerdeman, primarily attacks the roots of soybean [Glycine max (L.) Merr.] plants. Partial resistance and field tolerance in 14 commercial glyphosate [N-(phosphonomethyl)glycine] tolerant soybean cultivars with the Rps1k resistance gene were studied. Partial resistance to compatible P. sojae races 28 and 30 was evaluated by the agar layer technique. Relative to the percentage of the control, all of the commercial cultivars with the Rps1k had reductions in top mass and plant height that were not significantly different from the partial resistant check ‘Conrad’ that had 83% top mass and 77% plant height reduction; two of the 14 commercial cultivars had significantly lower root mass (28 and 31% lower) than Conrad (84%). In addition, there was no significant difference in disease ratings (root or whole plant) of the 14 commercial cultivars with the Rps1k compared with Conrad. Field tolerance, studied in six field experiments at Urbana, IL, during 2002–2004, was identified when there were no significant differences between the yield of inoculated treatments with or without mefenoxam [methyl N-(methoxyacetyl)-N-(2,6-xylyl)-D-alaninate] fungicide seed treatment or between inoculated and noninoculated treatments. There were no significant cultivar x inoculation x fungicide treatment interactions found in any of the field experiments, and a significant cultivar x inoculation treatment interaction was found in only one field experiment. Therefore, most of the cultivars appeared to be tolerant to P. sojae. It should be noted that field tolerance was not distinguished from partial resistance in the field component of this study.
  
  
  
• 2005: Bradley, C. A., G. L. Hartman, D. S. Mueller, D. D. Hoffman, A. D. Nickell, and W. L. Pedersen. 2005. Genetic analysis of partial resistance to Rhizoctonia solani in the soybean cultivar 'Savoy'. Canadian Journal of Plant Pathology 27:137-142. [link] [view abstract]
  Rhizoctonia solani is a soilborne pathogen that causes Rhizoctonia root rot. This disease is commonly found in most soybean-growing areas and can cause stand reduction and yield losses in soybean. A population from a cross between the soybean cultivar Savoy (partially resistance to R. solani) and Jack (susceptible to R. solani) was evaluated in the greenhouse. Reaction to R. solani in segregating F₂ and F₃ generations indicated that resistance was inherited as a quantitative trait. Heritability estimates indicated that selection for resistance to R. solani in soybean based on F_2:3 family means would be more efficient than selecting on a single F₂ plant basis. (Rhizoctonia root rot, caused by the fungus Rhizoctonia solani, is a common disease of soybean in the north central United States and causes pre- and postemergence damping off in addition to rotting of the hypocotyl and roots. A previous study, in which several soybean cultivars were evaluated for resistance to R. solani, reported that the cultivar Savoy had partial resistance, while the cultivar Jack was susceptible. The objectives of this study were to determine the inheritance of this partial resistance. A population from a cross between the soybean cultivar Savoy and Jack was evaluated in the greenhouse. Reaction to R. solani in segregating generations indicated that resistance was inherited as a quantitative trait. This is the first report of genetic analysis of resistance to R. solani in a soybean cultivar, and provides information that may allow soybean breeders to select lines with partial resistance to R. solani more efficiently.
  
  
  
• 2005: Lim, H.-S., Ko, T.-S., Lambert, K. N., Kim, H.-G., Korban, S. S., Hartman, G. L., and Domier, L. L. 2005. Soybean mosaic virus helper component-protease enhances somatic embryo production and stabilizes transgene expression in soybean. Plant Physiology and Biochemistry 43:1014-1021. [link] [view abstract]
  Soybean mosaic virus (SMV) helper component protease (HC-Pro), a suppressor of post-transcriptional gene silencing, was evaluated for its ability to enhance production of soybean hygromycin-resistant somatic embryos (HR-SEs), and stabilize transgene expression. Immature soybean cotyledonary explants were co-cultured with Agrobacterium tumefaciens strain KYRT1 harboring either pCAMBIA1302, carrying a hygromycin phosphotransferase gene (hpt) and a gene encoding green fluorescent protein; pCAMBIA1305.1, carrying hpt and β-glucuronidase (uidA) genes; pG2-HC-Pro, a derivative of pCAMBIA1305.1 containing SMV G2 HC-Pro; or pG5-HC-Pro, a derivative of pCAMBIA1305.1 containing SMV G5 HC-Pro, but lacking uidA. Significantly (ρ < 0.02) higher numbers of HR-SEs were obtained from explants transformed with Agrobacterium harboring either pG2-HC-Pro or pG5-HC-Pro than with either of the vector controls (pCAMBIA1302 or pCAMBIA1305.1). β-glucuronidase (GUS) expression was significantly (P < 0.003) higher in 50-day-old transgenic plants expressing GUS along with SMV-HC-Pro and in SMV-infected GUS transgenic plants than in transgenic plants expressing GUS alone. Together, these data suggest that SMV-HC-Pro enhanced recovery of HR-SEs by suppressing silencing of the hygromycin phosphotransferase gene.
  
  
  
• 2005: Miles, M. R., Morel, W., and Hartman, G. L. 2003. Summary of the USDA fungicide efficacy trials to control soybean rust in Paraguay 2002-2003. [Online]. http://www.ipmcenters.org/NewsAlerts/soybeanrust/efficacy.cfm. [download]
  
  
• 2005: Hartman, G. L., Miles, M. R., and Frederick, R. D. 2005. Breeding for resistance to soybean rust. Plant Dis. 89:664-666. [download]
  
  
• 2005: Miles, M. R., Hartman, G. L., and Frederick, R. D. 2005. Management of Asian soybean rust. Pages 23-27 in: Proceedings: 2005 Illinois Crop Protection Technology Conference University of Illinois Extension, Urbana. [download]
  
  
• 2005: Miles, M. R., Morel, W., Steinlage, T. A., and Hartman, G. L. 2004. Summary of the USDA fungicide efficacy trials to control soybean rust in Paraguay 2003-2004. [Online]. http://www.ipmcenters.org/NewsAlerts/soybeanrust/efficacy.cfm. [download]
  
  
• 2005: Wang, Y., H.A. Hobbs, C.B. Hill, L.L. Domier, G.L. Hartman, and R.L. Nelson. 2005. Evaluation of ancestral lines of U.S. soybean cultivars for resistance to four soybean viruses. Crop Sci. 45:639-644. [download] [view abstract]
  Fifty-two North American (NA) ancestral soybean [Glycine max (L.) Merr.] lines were screened for resistance to Bean pod mottle virus (BPMV), Soybean mosaic virus (SMV) strains G1 and G5, Tobacco ringspot virus (TRSV), and Tobacco streak virus (TSV). Seven ancestors, ‘CNS’, ‘Haberlandt’, ‘Ogden’, ‘Peking’, PI 71506, PI 88788, and ‘Tokyo’, were resistant to SMV-G1. Sixteen entries, ‘A.K. (Harrow)’, ‘Capital’, CNS, FC 33243, Haberlandt, ‘Illini’, ‘Improved Pelican’, ‘Laredo’, ‘Lincoln’, ‘Mandarin’, ‘Mandarin (Ottawa)’, Ogden, ‘Palmetto’, Peking, PI 88788, and Tokyo were resistant to SMV-G5. All ancestral lines tested were susceptible to BPMV and TRSV. Only one ancestor, ‘Tanner’, was resistant to TSV. On the basis of cultivar registration articles through 2002, there were 15 public soybean cultivars with reported resistance to SMV. The possible donors of resistance for each were identified. Two soybean ancestors, CNS and Ogden, were the most important possible sources of SMV resistance genes in U.S. commercial soybean cultivars, as the pedigree of 75 and 56% of the reported resistant cultivars contained CNS and Ogden, respectively. In most of the cultivar registration articles, reactions to SMV were not reported. With the relatively high frequency of SMV resistance in major ancestral lines, SMV resistance in U.S. cultivars may be more common than expected.
  
  
  
• 2005: Yorinori, J. T., Paiva, W. M., Frederick, R. D., Costamilan, L. M., Bertagnolli, P. F., Hartman, G. L., Godoy, C. V., and Nunes Jr., J. 2005. Epidemics of soybean rust (Phakopsora pachyrhizi) in Brazil and Paraguay from 2001 to 2003. Plant Dis. 89:675-677. [download]
  
  
• 2004: Hartman, G. L., Miles, M. R., and Frederick, R. D. 2004. Soybean rust: Historical significance and U.S. perspective. In Argentinian Conference on Mimimum Tillage in Agriculture. Buenos Aires Argentina. [link]
  
  
• 2004: Li, S., Kurtzweil, N. C., Grau, C. R., and Hartman, G. L. 2004. Occurrence of soybean stem canker (Diaporthe phaseolorum var. meridionalis) on soybean in Wisconsin. Plant Disease 88:576. [download] [view abstract]
  Soybean (Glycine max) developed symptoms characteristic of stem canker during the 2000 to 2003 growing seasons in Wisconsin. Symptoms were widespread in 2003 and were associated with yield losses of ª1% statewide, and as much as 25% in individual fields. Affected plants ex-pressed dieback of foliage beginning at growth stage R3 and progressed until the R6 growth stage. Dark brown lesions were frequently observed at a single node on the lower portion of stems of plants expressing foliage dieback. Fungi were isolated from symptomatic plants collected from seven growers’ fields in Rock, Sauk, Veron, and Walworth counties, and the Arlington and Marshfield Agricultural Research Stations. Stems with lesions were cut into 5-mm pieces, surface-disinfested with 0.5% NaOCl solution for 3 min, rinsed three times in sterile distilled water, and placed on water agar (WA) or potato dextrose agar (PDA) at pH 4.5. Hyphal tips from colonies of interest were excised and placed on acidi-fied PDA at 25∞C under continuous light for 25 to 30 days. In addition to Diaporthe phaseolorum var. caulivora, the cause of northern stem canker, four isolates of D. phaseolorum var. meridionalis, the cause of southern stem canker, were isolated. Colonies of D. phaseolorum var. meridionalis isolates were white, lanose, and turned tan with age as pre-viously described for D. phaseolorum var. meridionalis (1). Pycnidia with alpha conidia (no beta-conidia) and perithecia with 3.1 to 3.4 _ 9.5 to 9.8 µm ascospores formed on oat flakes on acidified WA after 30 days. Stromata were brown to black and irregularly shaped. Four isolates of D. phaseolorum var. meridionalis were tested for pathogenicity in a controlled environment using a cut stem inoculation method (2). Stems of 3 week old seedlings of the cultivar Sturdy were cut at the midpoint between the second and the third node, and a PDA mycelial plug (4 mm in diameter) was placed on the surface of the cut stems. This method was used to inoculate 15 plants, in three replicates, for each isolate tested. Inoculated plants were placed in a mist chamber in the dark at 25∞C for 4 days and later moved to a greenhouse with a 16-h photoperiod at 24 ± 3∞C for 3 days. All plants challenged by this method exhibited stem lesions 2 to 3 cm long and of similar color to lesions observed in field grown plants. For each isolate tested, D. phaseolorum var. meridionalis was reisolated from three randomly selected symptomatic plants. Negative controls with a PDA plug did not produce lesions. To our knowledge, this is the first report of D. phaseolorum var. meridionalis on soybean in Wisconsin. The significance of this report relates to the potential spread of D. phaseolorum var. meridionalis beyond its known southern range in the United States.
  
  
  
• 2004: Lozovaya, V. V., Lygin, A. V., Zernova, O. V., Li, S., Hartman, G. L., and Widholm, J. M. 2004. Isoflavonoid accumulation in soybean hairy roots upon treatment with Fusarium solani. Plant Phys. & Bioch. 42:671-679. [link] [view abstract]
  Hairy roots were initiated from two soybean [Glycine max (L.) Merr.] genotypes with different susceptibility (susceptible ‘Spencer’ and partially resistant ‘PI567.374’) to the disease sudden death syndrome (SDS) caused by the soil-borne fungal pathogen Fusarium solani f. sp. glycines (FSG) to study the role of isoflavonoids in the plant response to FSG infection. Hairy root cultures obtained by transformation with Agrobacterium rhizogenes allows normal root growth that can be visually monitored. The principal isoflavones (genistin, daidzin, glycitin and their malonyl conjugates and aglycones) and also isoflavonoid phytoalexins (coumestrol and glyceollin) were measured by HPLC in extracts of the FSG-inoculated and non-inoculated hairy roots. FSG mycelia grew more slowly on inoculated PI567.374 hairy roots than on Spencer hairy roots. The glyceollin content was higher in FSG-inoculated PI567.374 hairy roots than in Spencer hairy roots even though the glyceollin precursor, the isoflavone daidzein, was higher in Spencer. The de novo synthesis of isoflavones and glyceollin was confirmed by [14C]Phe incorporation into glyceollin, which was higher both in the FSG-inoculated roots and surrounding medium of the cv. PI567.374 than that of Spencer. Glyceollin was the most inhibitory to FSG growth among eight isoflavonoids tested. The levels of coumestrol, a putative phytoalexin, did not change upon FSG inoculation. The defense response was also elicited by FSG culture filtrates in hairy roots grown in liquid culture. The data obtained indicate that the ability of soybean roots to rapidly produce sufficient amounts of glyceollin in response to FSG infection might be important in providing partial resistance to this fungus.
  
  
  
• 2004: Gao, X., Jackson, T. A., Lambert, K. N., Li, S., Hartman, G. L., and Niblack, T. L. 2004. Detection and quantification of Fusarium solani f. sp. glycines in soybean roots with real-time quantitative polymerase chain reaction. Plant Dis. 88:1372-1380. [download] [view abstract]
  Fusarium solani f. sp. glycines is the causal organism of soybean sudden death syndrome (SDS). This organism is difficult to detect and quantify because it is a slow-growing fungus with variable phenotypic characteristics. Reliable and fast procedures are important for detection of this soybean pathogen. Protocols were optimized for extraction of DNA from pure fungal cultures and fresh or dry roots. A new procedure to test polymerase chain reaction (PCR) inhibitors in DNA extracts was developed. Novel real-time quantitative PCR (QPCR) assays were developed for both absolute and relative quantification of F. solani f. sp. glycines. The fungus was quantified based on detection of the mitochondrial small-subunit rRNA gene, and the host plant based on detection of the cyctophilin gene of the host plant. DNA of F. solani f sp. glycines was detected in soybean plants both with and without SDS foliar symptoms to contents as low as 9.0 x 10-5 ng in the absolute QPCR assays. This is the first report of relative QPCR using the comparative threshold cycle (Ct) method to quantify the DNA of a plant pathogen relative to its host DNA. The relative QPCR assay is reliable if care is taken to avoid reaction inhibition and it may be used to further elucidate the fungus-host interaction in the development of SDS or screen for resistance to the fungus.
  
  
  
• 2004: Kull, L. S., Pedersen, W. L., and Hartman, G. L. 2004. Mycelial compatibility and aggressiveness of Sclerotinia sclerotiorum. Plant Disease 88:325-332. [download] [view abstract]
  Population variability of Sclerotinia sclerotiorum, the causal organism of Sclerotinia stem rot of soybean, was determined by mycelial compatibility grouping (MCG) and isolate aggressiveness comparisons. MCG and aggressiveness of S. sclerotiorum isolates from diverse hosts and geographic locations (Diverse Set, 24 isolates), from a soybean field in Argentina (Argentine Set, 21 isolates), and from soybean fields in DeKalb and Watseka, Illinois (DeKalb and Watseka Sets, 125 and 135 isolates, respectively) were assessed. Among 305 isolates tested, 42 MCGs were identified, and 61% were represented by single isolates observed at single locations. Within the Diverse Set, 17 MCGs were identified; one MCG consisted of six isolates, and 16 MCGs consisted of one isolate each. Each Illinois field was a mosaic of MCGs, but MCG profiles differed between the two fields. Nine MCGs were identified within the Argentine field with two MCGs composed of either five or six isolates, two MCGs composed of two isolates, and the remaining composed of one isolate each. MCGs were shared among the Diverse, DeKalb, and Watseka Sets, but MCGs within the Argentine Set were not shared with other sets. MCGs within the DeKalb and Watseka Sets were spatially aggregated based upon sampling location within the field. MCG 8 was the most frequently sampled and widely distributed MCG and occurred at a frequency of 29, 36, and 62% in the Diverse, DeKalb, and Watseka Sets, respectively. Variation in isolate aggressiveness was assessed using a limited-term, plug inoculation technique and area under the disease progress curve (AUDPC) was calculated for each isolate. Isolate aggressiveness varied (P=0.001) within the Diverse, DeKalb, Watseka, and Argentine Sets and varied (P<0.10) within MCGs composed of isolates from different locations, but did not vary within MCGs composed of isolates from a single field. Additionally, MCGs within the DeKalb and Watseka Sets differed in aggressiveness. A cultivar x isolate interaction was not detected, but resistant and susceptible cultivars performed similarly when inoculated with either less or highly aggressive isolates. Pathogen population structure and isolate variability may be important considerations in disease management systems.
  
  
  
• 2004: Vuong, T. D., D. D. Hoffman, B. W. Diers, J. F. Miller, J. R. Steadman, and G. L. Hartman. 2004. Evaluation of soybean, dry bean, and sunflower for resistance to Sclerotinia sclerotiorum. Crop Sci. 44:777-783. [download] [view abstract]
  Many inoculation methods have been used to evaluate resistance of different crops to Sclerotinia sclerotiorum (Lib.) de Bary. Only a few of these methods have been used to evaluate more than one crop. This study compared disease evaluations of soybean [Glycine max (L.) Merr.], dry bean (Phaseolus vulgaris L.), and sunflower (Helianthus annuus L.) inoculated in the greenhouse (cut stem inoculation method) to field evaluations. In one experiment, stems of two soybean cultivars, ‘Williams 82’ (susceptible) and ‘NKS19-90’ (partially resistant), were severed and inoculated with a colonized mycelial plug of S. sclerotiorum placed on top of the plant at the cut point of the stem. Stem lesion lengths on these two cultivars were used to determine what affect plant age and post-infection temperature had on disease development. There was a significant (P<0.05) difference in lesion lengths between inoculated 5-wk-old plants compared to 6- or 7-wk-old plants within each cultivar. At different post-infection temperatures, lesions developed at 25°C but not at 30°C. In another experiment, disease rating of 15 soybean cultivars evaluated in the greenhouse and field had significant (P<0.05) correlation coefficients from 0.53 to 0.79. In addition to soybean, two experiments were completed on dry bean and sunflower. There were significant (P<0.05) differences in lesion lengths among 14 genotypes of each, dry bean and sunflower. The correlation between greenhouse and field evaluations of dry bean and sunflower were 0.74 and 0.50 (P<0.05), respectively. In summary, disease assessments from the cut stem inoculation compared favorably to disease assessments in the field for soybean, dry bean, and sunflower.
  
  
  
• 2004: Hartman, G. L., Bonde, M. R., Miles, M. R., and Frederick, R. D. 2004. Variation of Phakopsora pachyrhizi isolates on soybean. Pages 440-446 in: Proceedings of VII World Soybean Research Conference, IV International Soybean Processing and Utilization Conference, III Congresso Mundial de Soja (Brazilian Soybean Conference), F. Moscardi, et al., eds. Embrapa Soybean, Londrina. [download] [view abstract]
  Phakopsora pachyrhizi Sydow, the causal fungus of soybean (Glycine max (L.) Merrill) rust, occurs in most soybean-growing areas of the world except continental North America. Initial studies on soybean rust isolates from the Western Hemisphere indicated that they were different than isolates from the Eastern Hemisphere. In 1992, the Eastern Hemisphere species, P. pachyrhizi, and the Western Hemisphere species, P. meibomiae, were established for the soybean rust fungi based on morphological differences. The first molecular differentiation of the two species was reported in 2002. A number of studies have reported the occurrence of race in P. pachyrhizi either on soybeans or on other hosts. In 1984, a set of four native Australian Glycine species were used to identify six different virulence combinations of P. pachyrhizi. Much of the research on differentiating isolates on soybean was completed in a containment facility at in the U.S. Genetic characterization on four plant introductions (PIs) indicated the occurrence of four independently inherited dominant genes. These genes are known to be effective to a limited number of isolates. There are many studies that need to be completed to determine if all isolates respond equally in terms of survival, urediniospore production, telia formation, and host range under different environments. Over the next few years, our understanding of pathogen diversity will increase as more concerted research efforts take place in different parts of the world.
  
  
  
• 2004: Miles, M. R., Morel, W., Yorinori, J. T., Ma, Z.-H., Poonpolgul, S., Hartman, G. L., and Frederick, R. D. 2004. Preliminary report of Asian soybean rust reaction on soybean accessions planted in Brazil, China, Paraguay and Thailand with seedling reactions from greenhouse screens in the United States. Page 162 in: Documentos 228: Abstracts of contributed papers and posters VII World Soybean Research Conference, IV International Soybean Processing and Utilization Conference, III Congresso Mundial de Soja, F. Moscardi, et al., eds. Embrapa Soybean, Londrina. [download] [view abstract]
  Asian soybean rust, Phakopsora pachyrhizi, has been an important pathogen of soybean in Asia with yield losses of 40 to 80% commonly reported. The pathogen has moved into Africa, where it was reported in Uganda in 1996, then Zimbabwe (1998) and South Africa (2001). The pathogen was first found South America in Paraguay and then Brazil during the 2001 growing season. A set of 174 soybean accessions was evaluated against local soybean rust populations in field or greenhouse studies in Brazil, China, Paraguay, and Thailand. The materials were also evaluated in the USDA BSL-3 containment greenhouse in Ft. Detrick, MD against a mixed collection of P. pachyrhizi from Brazil, Paraguay, Thailand and Zimbabwe. Among the set were soybeans that had previously been reported to have resistance to either P. pachyrhizi or P. meibomia, including the sources of the four identified resistance genes. The pathogen is known to have a complex and diverse virulence pattern with many phenotypes seen within a field collection. This was observed as mixed resistant (RB) and susceptible reactions on several lines within each location. Disease severity and reaction phenotypes on individual lines differed by location. These differences were due to local environmental conditions, which reduced rust severity as well as differences in the virulence of the rust population at each location. No lines were found to be resistant at all locations.
  
  
  
• 2004: Miles, M. R., Blaine, A., Tingle, C., Lancos, D., Draper, M., Giesler, L., Hartman, G. L., and Pedersen, W. 2004. Evaluation of fungicide application methods in post flowering soybeans to support recommendations for control of soybean rust, Phakopsora pachyrhizi, preliminary report. Pages 230-1 in: Documentos 228: Abstracts of contributed papers and posters VII World Soybean Research Conference, IV International Soybean Processing and Utilization Conference, III Congresso Mundial de Soja, F. Moscardi, et al., eds. Embrapa Soybean, Londrina. [download] [view abstract]
  Asian soybean rust is one of the most devastating diseases of soybean with yield losses of 10 to 100% reported. The disease is found primarily in the lower canopy before flowering and in the middle and upper canopy after flowering. Heavily infected plants often prematurely defoliate causing significant yield losses. Until useful genetic resistance can be identified and moved into commercial cultivars, fungicides will be the primary means to control the disease. There is not much information on fungicide application in soybean. Fungicide use in soybean has been limited to seed treatments and a single late season foliar. With soybean rust the canopy needs to be protected from onset of flowering through pod fill. The research presented is a preliminary summary of the measurement of canopy penetration using high and low water volumes with two fungicides, Bravo and Quadris. Fungicides were applied aerially at 5 and 10 gal/ac in six locations in the southern US and by ground in three locations in the midwest US. In the ground application experiment, air induction, flat fan pointed down, flat fans on drops set to spray 105° and twin jet on forward facing right angle drops set to spray 80° nozzles were compared. Field design was set up as a strip plot with at least three replications per location. Three water sensitive paper strips were placed at mid canopy across the spray swath in three locations the length of the plot. Increased water volume in both ground and aerial application improved fungicide coverage when compared to the lower application volume. Among the nozzle tips evaluated in ground applications, overhead flat fans provided the least fungicide coverage in mid canopy.
  
  
  
• 2004: Li, Y., Hill, C. B., and Hartman, G. L. 2004. Effect of three resistant soybean genotypes on the fecundity, mortality, and maturation of the soybean aphid, Aphis glycines (Homoptera: Aphididae). Journal of Economic Entomology 97:1106-1111. [download] [view abstract]
  The fecundity, longevity, mortality, and maturation of the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), were characterized using three resistant soybean, Glycine max (L.) Merrill, genotypes ('Dowling', 'Jackson', and PI200538 'Sugao Zarai') and two susceptible genotypes ('Pana' and 'Loda'). Antibiosis in the resistant genotypes was demonstrated by a significant decrease in fecundity and longevity and increased mortality of A. glycines. Aphid fecundity, measured as number of offspring produced in the first 10 d by each viviparous aptera, was higher on Pana than on the resistant genotypes. Aphid longevity, the mean number of days a 1-d-old adult lived, was 7 d longer on Pana than on Dowling and Jackson. The mortality of both viviparous apterae and nymphs on resistant genotypes was significantly higher than on susceptible genotypes. A greater number of first instars survived to maturation stage (date of first reproduction) on susceptible plants than on resistant plants. None of the first instars placed on Dowling and PI200538 leaves survived to maturation. Observations of aphid behavior on leaves indicated that aphids departed from the leaves of resistant plants 8 -24 h after being placed on them, whereas they remained indefinitely on leaves of susceptible cultivars and developed colonies. Reduced feeding due to ingestion of potentially toxic compounds in soybean may explain the possible mechanism of resistance to the soybean aphid. KEY WORDS Aphis glycines, aphid longevity, feeding preferences, host resistance, soybean aphid.
  
  
  
• 2004: Hill, C. B., Li, Y., and Hartman, G. L. 2004. Resistance of Glycine species and various cultivated legumes to the soybean aphid (Homoptera: Aphididae). J. of Econ. Entomol. 97:1071-1077. [download] [view abstract]
  ABSTRACT The soybean aphid, Aphis glycines Matsumura, is a new pest of soybean, Glycine max (L.) Merr., in North America. It has become widespread on soybean in North America since it was first identifed in the Midwest in 2000. Species of Rhamnus L. (buckthorn) are the primary hosts of A. glycines, and soybean is known as a secondary host. There is limited information about the secondary host range of A. glycines. Aphid colonization on variouslegume hostswascompared in choice experiments. Aphid colonization occurred on species in the genus Glycine Wild. No colonization occurred on Lablab purpureus (L.) Sweet, Lens culinaris Medik, Phaseolus vulgaris L., Pisum sativum L., or species of Vicia L. and Vigna Savi. Colonization was limited or aphids were transient on species of Medicago L., Phaseolus L., and Trifolium L. There were significant differences in aphid colonization among Medicago truncatula accessions with numbers ranging from 7 to 97 aphids per plant. Six Glycine soja Sieb.&Zucc. accessions were as resistant as G. max accessions to A. glycines; these may represent novel sources of A. glycines resistance not found in G. max. Antibiosis was found to play a large role in the expression of resistance in three of the G. soja accessions. Results of this study indicated that G. max and G. soja were the best secondary hosts of A. glycines; however, its secondary host range may include other leguminous species. Therefore, A. glycines did not seem to have a highly restricted monophagous secondary host range.
  
  
  
• 2004: Hill, C. B., Li, Y., and Hartman, G. L. 2004. Resistance to the soybean aphid in soybean germplasm. Crop Sci. 44:98-106. [download] [view abstract]
  With an efficient greenhouse screening method, the first resistance to the soybean aphid (Aphis glycines Matsumura) was found in culti¬vated soybean [Glycine max (L.) Merr.] germplasm. No resistance was found in 1425 current North American soybean cultivars, 106 Maturity Group (MG) 000 through VII Asian cultivars, and in a set of 11 'Clark' isolines possessing different pubescence traits. Dense pubescence did not provide protection against the soybean aphid. Resistance was discovered and established in three ancestors of North American genotypes: 'Dowling', 'Jackson', and PI 71506. Expression of resis¬tance in those genotypes was characterized in choice and nonchoice tests. In choice tests, significantly fewer aphids occurred on Dowling, Jackson, and PI 71506 plants compared with susceptible cultivars (P = 0.05). Aphid populations did not develop on Dowling and Jackson in nonchoice tests, indicating that there was a negative impact on aphid fecundity on those cultivars. That evidence combined with ob¬servations of aphid mortality on those cultivars suggested that antibio¬sis-type resistance contributed to the expression of resistance. Possible donors of resistance to Dowling and Jackson were identified. In non-choice tests, population development on PI 71506 was not sig¬nificantly different from development on susceptible cultivars, indicat¬ing that antixenosis was more important in that genotype. Resistance was expressed in all plant stages. Dowling provided season-long pro¬tection against aphids equal to the use of the systemic insecticide imi-dadoprid {l-[(6-Chloro-3-pyridinyl)methyl]-Ar-nitro-2-imidazolidini-mine) in a field test. Four other germplasm accessions, 'Sugao Zarai', 'Sato', 'T260H', and PI 230977, had levels of resistance not significantly different from Dowling, Jackson, and PI 71506 in a choice test (P = 0.05).
  
  
  
• 2004: Lozovaya, V. V., Lygin, A. V., Li, S., Hartman, G. L., and Widholm, J. M. 2004. Biochemical response of soybean roots to Fusarium solani f. sp. glycines infection. Crop Science 44:819-826. [download] [view abstract]
  The soil-borne fungus, Fusarium solani f. sp. glycines (FSG), infects soybean roots and causes the disease sudden death syndrome. The biochemical response of soybean roots to FSG infection, that has not been studied before, was investigated by comparing FSG-inoculated and non-inoculated roots of two partially resistant (PI520.733 and PI567.374) and susceptible (Spencer) genotypes. Activity of phenylalanine ammonia-lyase, the first enzyme in the phenylpropanoid biosynthetic pathway, was greater in inoculated than non-inoculated plants of all three genotypes. The phytoalexin glyceollin increased to much higher levels in roots of the partially resistant cvs. PI520.733 and PI567.374 than in the susceptible Spencer. The changes in phenolic metabolism were much greater in lesion containing areas of roots than in the new portion growing under the FSG inoculum. No clear correlation was found between the glyceollin precursor daidzein and its conjugates and glyceollin levels in root tissues; however, isoflavone levels increased only in roots of inoculated plants of partially resistant lines, even though constitutive isoflavone levels were higher in the susceptible control. FSG growth on potato dextrose agar medium was inhibited by increasing concentrations of glyceollin. Induction of lignin synthesis was found in the inoculated roots of all three lines, with the highest rate of lignification observed in roots of the partially resistant genotypes, especially PI567.374. These studies show that FSG inoculation of soybean roots in soil induces the phenylpropanoid pathway to synthesize isoflavones, the phytoalexin glyceollin and lignin, indicating that these compounds may be involved in the partial resistance response.
  
  
  
• 2004: Miles, M. R., Levy, C., and Hartman, G. L. 2004. Summary of the USDA fungicide efficacy trials to control soybean rust in Zimbabwe 2003-2004. [Online]. http://www.ipmcenters.org/NewsAlerts/soybeanrust/efficacy.cfm. [download]
  
  
• 2004: Hartman, G. L., Huang, Y. H., and Li, S. 2004. Phytotoxicity of Fusarium solani culture filtrates from soybean and other hosts assayed by stem cuttings. Australasian Plant Pathology 33:9-15. [download] [view abstract]
  Fusarium solani infects roots of a number of different plant species and some strains produce phytotoxins. F. solani f. sp. glycines, the causal organism of sudden death syndrome (SDS) of soybean (Glycine max), colonizes soybean roots and produces toxin(s) that are translocated to leaves and cause intervienal chlorosis and necrosis. Several experiments evaluated the phytotoxicity of cell-free culture filtrates of F. solani f. sp. glycines by immersing cuttings of soybean seedlings into filtrates to determine what in vitro growth conditions alter the phytotoxicity, and to determine the specificity of toxicity of F. solani f. sp. glycines and other F. solani on cuttings of soybean and other legume species. Foliar disease severity ratings of soybean cuttings in cell-free culture filtrates diluted 25- and 50-fold were higher than when diluted 100-fold or more. Cell-free culture filtrates originating from cultures grown at 15, 20, and 25˚C caused greater (P = 0.05) foliar disease severity ratings on cutting than when the fungus was grown at 30˚C. Cell-free culture filtrates of F. solani isolates from cucumber (Cucumis sativus) and pumpkin (Cucurbita pepo) did not cause symptoms on soybean cuttings while filtrates of F. solani isolates obtained from other hosts caused some leaf chlorosis and/or necrotic spots. F. solani f. sp. glycines inoculated on eight legume species caused symptoms such as leaf chlorosis, defoliation, wilt or death on most of the species, but azuki bean (Vigna angularis), common pea (Pisum sativum) and vetch (Vicia sativa) were symptomless. Cell-free culture filtrates of F. solani f. sp. glycines caused foliar symptoms on all cuttings of legume species except for mung bean (Vigna radiata), although none of the symptoms matched the SDS symptoms observed on soybean foliage.
  
  
  
• 2003: Hartman, G. L., Miles, M. R., and Frederick, R. D. 2003. Soybean rust: Will resistance work? Pages 7-13 in: Proceedings of the 15th Annual Integrated Pest Management Conference, Dec. 3-4, 2003 Iowa State University Extension, Ames, Iowa. [link]
  
  
• 2003: Miles, M. R., Frederick, R. D., and Hartman, G. L. 2003. Management strategies for the control of soybean rust. Pages 13-22 in: Proceedings of the 15th Annual Integrated Pest Management Conference, Dec. 3-4, 2003 Iowa State University Extension, Ames, Iowa. [link]
  
  
• 2003: Miles, M. R., Hartman, G. L., and Frederick, R. D. 2003. Soybean rust: Is the U.S. crop at risk? [Online]. http://www.apsnet.org/online/feature/rust. [link]
  
  
• 2003: Zhang, Z. D., Ma, Z. H., Wang, Y. X., Yang, X. B., Hartman, G. L., Miles, M. R., and Frederick, R. D. 2003. Screening soybean germplasm against soybean rust in China. In Proceedings: 15th International Plant Protection Congress. [link]
  
  
• 2003: Bradley, C. A., Noel, G. R., Grau, C. R., Gaska, J. M., Kurtweil, N. C., MacGuidwin, Hartman, G. L., Wax, L. M., and Pedersen, W. L. 2003. Impact of herbicides on Heterodera glycines susceptible and resistant soybean cultivars. Journal of Nematology 35:88-97. [link]
  
  
• 2003: Domier, L. L., Latorre, I. J., Steinlage, T. A., McCoppin, N., and Hartman, G. L. 2003. Variability and transmission of Aphis glycines of North American and Asian soybean mosaic virus isolates. Archives of Virology 148:1925-1941. [link]
  
  
• 2003: Li, S., and Hartman, G. L. 2003. Molecular detection of Fusarium solani f. sp. glycines in soybean roots and soil. Plant Path. 52:74-83. [link] [view abstract]
  A polymerase chain reaction (PCR)-based method was developed to detect DNA of Fusarium solani L sp. glycines, the cause of soybean sudden death syndrome. Two pairs of primers, Fsg1/Fsg2 designed from the mitochondrial small subunit ribosomal RNA gene, and FsgEF1/FsgEF2 designed from the translation elongation factor 1-± gene, produced PCR products of 438 and 237 bp, respectively. Primer specificity was tested with DNA from 82 F. solani f. sp. Glycines, 55 F. solani non-SDS isolates, 43 isolates of 17 soybean fungal pathogens and the oomycete Phytophthora soja, and soybean. The sensitivity of primer Fsg1/Fsg2 was 10 pg while that of FsgEF1/FsgEF2 was 1 ng when using F. solani f. sp. glycines total genomic DNA or down to 103 macroconidia g-1 soil Nested PCR increased the sensitivity of the PCR assay 1000-fold to 10 fg using primers Fsg1/Fsg2, and 1 pg using primers FsgEF1/FsgEF2. f. solani f. sp. glycines DNA was detected in field-grown soybean roots and soil by PCR using either single pairs of primers or the combination of two pairs of primers. The occurrence of F. solani f. sp.glycines was determined using nested PCR for 47 soil samples collected from soybean fields in 20 counties of Illinois in 1999. F. solani f. sp. glycines was detected in soil samples from all five Illinois Agricultural Statistic Districts including 100, 89, 50, 92 and 50% of the samples from East, Central, North-east and West District, respectively.
  
  
  
• 2003: Vuong, T. D., and Hartman, G. L. 2003. Evaluation of soybean resistance to Sclerotinia stem rot using reciprocal grafting. Plant Dis. 87:154-158. [download] [view abstract]
  Sclerotinia stem rot of soybean is one of the major soybean diseases in the North Central region of the United States. One disease management option is to plant cultivars that have partial resistance. Although sources of partial resistance have been identified, information pertaining to the nature of resistance to Sclerotinia stem rot is limited. The objective of this study was to determine the expression of resistance by using combinations of susceptible and partially resistant shoots. Resistant and susceptible soybean genotypes were grafted in different shoot and rootstock combinations of self-, single- or double-scion grafts. After successful grafts were made, cotyledons were inoculated with a plug of fungal mycelium. Based on seven grafting combinations of cross- and self-grafted plants using two soybean cultivars, grafts with NKS19-90 (partially resistant) as shoots had greater (P < 0.05) plant survival than the other graft combinations. In another experiment, a total of 17 graft combinations were generated using resistant plant introductions, PI549.076A, PI503.336, and PI194.639, and two susceptible cultivars, Alpha and Merit. Resistant self-grafts of PI194.639, PI503.336, and PI549.076A, had greater (P < 0.05) plant survival than those of Alpha or Merit. Most inter-genotypic grafts with resistant shoots had greater plant survival than those in reciprocal combinations. In a double-graft experiment, shoots each of NKS19-90 and Williams 82 were grafted to either NKS19-90 or Williams 82 rootstocks. Regardless of the rootstock, the shoots of Williams 82 died while shoots of NKS19-90 survived. A resistant or susceptible response was consistently associated with resistant or susceptible shoots regardless of the rootstock, type of grafting technique, or inoculation method, indicating that shoot are expression of partial resistance to S. sclerotiorum is not affected by root characteristics.
  
  
  
• 2003: Kull, L. S., Vuong, T. D., Powers, K. S., Eskridge, K. M., Steadman, J. R., and Hartman, G. L. 2003. Evaluation of resistance screening methods for Sclerotinia stem rot of soybean and dry bean. Plant Dis. 87:1471-1476. [download] [view abstract]
  Data from three screening methods used to identify levels of resistance to Sclerotinia sclerotiorum for soybean (Glycine max) and dry bean (Phaseolus vulgaris) genotypes were compared by five statistical methods. Analysis of variance and mean separation tests were used to separate genotypes by resistance level and isolates by aggressiveness level. Six S. sclerotiorum isolates of known relative aggressiveness, and three soybean and three dry bean genotypes with varying levels of resistance to S. sclerotiorum were utilized. The three screening methods were mycelial plug inoculations of cotyledons, cut stems, and detached leaves. For soybean, all three inoculation methods accurately identified isolate aggressiveness levels irrespective of cultivar, but identification of susceptible and partially resistant soybean cultivars was influenced by isolate. For dry bean, the cotyledon and cut stem methods accurately identified isolate aggressiveness levels, but identification of susceptible and partially resistant dry bean cultivars was influenced by isolate and inoculation method. The cut stem method had the smallest coefficient of variation, was more precise at detecting interactions, and correlated with the other two methods. The sensitivity ratio showed the cut stem method to be superior to both other methods. The cotyledon method approached the technical merit of the cut stem method for both soybean and dry bean. When considering all five statistical analyses of resistance screening methods under controlled environmental conditions, the cut stem method was superior to the cotyledon method which was superior to the detached leaf method.
  
  
  
• 2003: Mueller, D. S., Hartman, G. L., Nelson, R. L., and Pedersen, W. L. 2003. Response of commercially developed soybean cultivars and the ancestral soybean lines to Fusarium solani f. sp. glycines. Plant Disease 87:827-831. [download] [view abstract]
  Sudden death syndrome, caused by Fusarium solani f. sp. glycines, has caused severe damage to soybean production in recent years. One way to control sudden death syndrome is with resistant cultivars. Over a 3-year period, 2335 publicly and privately developed soybean entries were inoculated and evaluated for their response to F. solani f. sp. glycines under greenhouse conditions. The entries were compared to the susceptible check, Great Lakes 3302 (GL3302), and the moderately resistant checks, plant introductions (PI) 520733 and 567374. Thirty-eight entries were identified with moderate levels of resistance. Based on foliar ratings, there were no differences (P<0.05) between the Roundup Ready and conventional cultivars. Ninety ancestral lines that represent 99% of the genes in modern U.S. cultivars and 55 lines found in the pedigrees of public cultivars reported to have some resistance were evaluated for their response to F. solani f. sp. glycines. Nine ancestral lines (Aoda , Kim, Jackson, Sioux, Mammoth Yellow, T117, PI 171450, PI 54615-1, and PI 71506) and 12 cultivars or experimental lines (Ina, D83-3349, LN98-4340, LN83-2356, Hartwig, Harosoy, Bedford, Merit, Cutler, Calland, Hill, and Evans) had disease ratings not significantly different (P<0.05) from PI 520733 or PI 567374. PI 54610, a putative ancestral line, was also found to be moderately resistant.
  
  
  
• 2003: Hobbs, H. A., Hartman, G. L., Wang, Y., Hill, C. B., Bernard, R. L., Pedersen, W. L.., and Domier, L. L. 2003. Occurrence of seed coat mottling in soybean plants inoculated with Bean pod mottle virus and Soybean mosaic virus. Plant Dis. 87:1333-1336. [download] [view abstract]
  Soybean seed coat mottling often has been a problematic symptom for soybean growers and the soybean industry. The percentages of seed in eight soybean lines with seed coat mottling were evaluated at harvest after inoculating plants during the growing season with Bean pod mottle virus (BPMV), Soybean mosaic virus (SMV), and both viruses inside an insect-proof cage in the field. Results from experiments conducted over 2 years indicated that plants infected with BPMV and SMV, alone or in combination, produced seed coat mottling, whereas noninoculated plants produced little or no mottled seed. BPMV and SMV inoculated on the same plants did not always result in higher percentages of mottled seed compared with BPMV or SMV alone. There was significant virus, line, and virus-line interaction for seed coat mottling. The non-seed-coat-mottling gene (Im) in Williams isoline L77-5632 provided limited, if any, protection against mottling caused by SMV and none against BPMV. The Peanut mottle virus resistance gene Rpvl in Williams isoline L85-2308 did not give any protection against mottling caused by SMV, whereas the SMV resistance gene Rsvl in Williams isoline L78-379 and the resistance gene or genes in the small-seeded line L97-946 gave high levels of protection against mottling caused by SMV. The correlations (r = 0.77 for year 2000 and r = 0.89 for year 2001) between virus infection of the parent plant and seed coat mottling were significant (P = 0.01), indicating that virus infection of plants caused seed coat mottling.
  
  
  
• 2003: Mabry, T. R., Hobbs, H. A., Steinlage, T. A., Johnson, B. B., Pedersen, W. L., Spencer, J. L., Levine, E., Isard, S. A., Domier, L. L., and Hartman, G. L. 2003. Distribution of leaf feeding beetles and Bean pod mottle virus (BPMV) in Illinois and transmission of BPMV in soybeans. Plant Dis. 87:1221-1225. [download] [view abstract]
  Bean leaf beetles (BLB; Cerotoma trifurcata) were collected in soybean (Glycine max) fields in 58 and 99 Illinois counties surveyed during the 2000 and 2001 growing seasons, respectively. In 2000 BLB counts were highest in the central portion of the state BLB counts were lower the following year, but were more uniformly distributed throughout the state. BLB tested positive forr Bean pod mottle virus (BPMV) in 37 of 41 counties assayed in 2000. In 2001, BLB tested positive for BPMV in 86 of 99 counties sampled. In 2000 and 2001, western corn rootworm (WCR; Diabrotica virgifera virgifera) adults were abundant in soybean fields only in east central Illinois. WCR adults tested positive for BPMV in 21 of 21 east central Illinois counties in 2000 and 20 of 24 sampled in 2001. BPMV was detected in soybean plants in 38 of 46 counties sampled in 2000. Field-collected WCR adults transmitted BPMV to potted soybean plants at low rates either directly from BPMV-infected soybean fields or with prior feeding on BPMV-infected plants. This is the first report of the distribution of BLB, WCR adults, and BPMV in Illinois and of BPMV transmission by adult WCR.
  
  
  
• 2003: Miles, M. R., Hartman, G. L., Levy, C., and Morel, W. 2003. Current status of soybean rust control by fungicides. Pesticide Outlook 14:197-200. [download] [view abstract]
  This paper focuses on the Asian soybean rust (Phakopsora pachyrhizi), the fungicides so far evaluated to control this disease, including the corresponding country where each fungicide was tested, as well as the individual summaries of application trials and recommendations. The importance of the timing and number of applications to control the disease, and the factors determining the number of applications (length of the reproductive phase of the crop, persistence of the compound and severity of the epidemic) are also emphasized. Among the most effective fungicides from trial done in Southern Africa were flusilazole + carbendazim, difenoconazole, and triadimenol. Trials in South America have identified several triazoles (tebuconazole and tetraconazole) as well as several strobularins and strobularin mixes ( azoxystrobin, pyraclostrobin, pyraclostrobin + boscalid and trifloxystrobin + propoconazole). The recommendations for control of the disease based on the experience in Southern Africa were two applications with the first application times 50 days after planting, at or before flowering, and a second application 20 days later.
  
  
  
• 2003: Hartman, G. L., Miles, M. R., and Frederick, R. D. 2003. Epidemiology and spread of soybean rust. In 2003 Corn & Sorghum and Soybean Conference: American Seed Trade Association Pub. No. 33. [download]
  
  
• 2002: Yu, G. Y., Sinclair, J. B., Hartman, G. L., and Bertagnolli, B. L. 2002. Produciton of iturin A by Bacillus amyloloiquefaciens supressing Rhizoctonia solani. Soil Biology & Biochemistry 34:955-963. [link] [view abstract]
  Bacillus amyloliquefaciens strain B94 was used as a biocontrol agent to suppress Rhizoctonia solani and other fungal plant pathogens. Three major antifungal compounds were purified from its culture broth, each has an amino acid composition consisting of Asn, Gln, Ser, Pro, and Tyr in a molar ratio of 3:1:1:1:1. Fast atom bombardment mass spectrometry/mass spectrometry (FAB MS/MS) collision induced dissociation (CID) analysis show that the antifungal compounds were three isomers of iturin A, a cyclic lipopeptide antibiotic produced by Bacillus subtilis. One of the major compounds with a molecular weight of 1042.5533 was identified as iturin A2. The peptide backbone of this compound was opened chemically, and the resulting linear peptide partially sequenced using the Edman degradation method. The results confirmed the results of FAB MS/MS CID analysis. A new reliable method for isolation and purification of iturin A and related compounds from bacterial broth culture was developed. The CID spectrum of iturin A could be used as a “fingerprint” to identify iturin A in a variety of mixtures.
  
  
  
• 2002: Li, S., Hartman, G. L., Jarvis, B. B., and Tak, H. 2002. A Stachybotrys chartarum isolate from soybean. Mycopathologia 154:41-49. [link] [view abstract]
  Stachybotrys chartarum was isolated from root lesions of soybean. Fungal morphology was examined using light and environmental scanning electron microscopy. Conidia were unicellular, round or ellipsoidal, 5-13 x 4-7 ºm, initially hyaline with smooth walls then dark brown to black and rough-walled when mature. Pathogenicity was performed using sorghum grain colonized by S. chartarum placed below sown soybean seeds in soil:sand (1:1) steam-pasteurized mix. Three weeks after inoculation, root lesions ranged from 7 to 25 mm long. The fungus was reisolated from soybean root lesions and was reidentified as S. chartarum. Biochemical analysis indicated that this soybean isolate produced satratoxins G and H along with roridin L-2, as well as the spircyclic lactones and lactams in rice culture. The DNA sequence of the ITS region was 100% identical to the S. chartarum strain ATCC 9182, one nucleotide mismatch with S. chartarum strain UAMH 7900, and differed from all published sequences of other Stachybotrys and Memnoniella species in GenBank with genetic divergence ranging from 5.26 to 9.98%. PCR using a S. chartarum-specific primer StacR3 and IT51 amplified a 198-bp DNA fragment from the total genomic DNA. This molecular evidence further supports the identification of S. chartarum isolated from soybean root lesions.
  
  
  
• 2002: Bradley, C. A., Hartman, G. L., Wax, L. M., and Pedersen, W. L. 2002. Influence of herbicides on Rhizoctonia root and hypocotyl rot of soybean. Crop Protection 21:679-687. [link]
  
  
• 2002: Mueller, D. S., Hartman, G. L., and Pedersen, W. L. 2002. Effect of crop rotation and tillage on Sclerotinia sclerotiorum on soybean. Canadian Journal of Plant Pathology 24:450-456. [download] [view abstract]
  Sclerotinia stem rot (SSR) of soybean is a major disease In the North Central region of the United States. A 3-year study was done to determine if crop rotation and tillage, moldboard plowing then mulch tillage (MP + MT}, mulch tillage (MT), and no-till (NT), affected the population density of sclerotia and apothecia, incidence of SSR, and soybean yield. Crop rotation did not significantly affect the number or distribution of sclerotia or SSR incidence, but did affect the number of apothecia and the yield. The highest number of apothecia per square metre was observed in the plots in the continuous soybean rotation. Tillage affected both the number and distribution of sclerotia in the soil profile. Moldboard plowing lowered the number of sclerotia per litre of soil, compared to MT and NT plots, and buried the sclcrotia deeper than 10 cm into the soil. Tillage did not affect the total number of apothecia observed, but moldboard plowing did delay emergence of apothecia compared to no-till. The MP + MT plots had the lowest disease incidence and the highest yield, while the NT plots had the highest disease incidence and (he lowest yields. One year of moldboard plowing will bury sclerotia at least 10 cm in soil and delay the production of apothecia. How this affects SSR development depends on the other factors involved with disease development.
  
  
  
• 2002: Bradley, C. A., Hartman, G. L., Wax, L. M., and Pedersen, W. L. 2002. Quality of harvested seed associated with soybean cultivars and herbicides under weed-free conditions. Plant Disease 86:1036-1042. [download] [view abstract]
  Field plots planted to different soybean cultivars located at four locations in Illinois were established between 1997 and 2000. Different weed management treatments were applied to the soybean plants, and varied from handweeded to preemergence herbicides to postemergence herbicides, and soybean seed was harvested and evaluated for different seed quality parameters. Herbicides had little or no effect on seed quality parameters such as percentage germination, incidence of seed pathogens, and protein and oil concentrations. Soybean seed quality was affected by Phomopsis spp. and Cercospora kikuchii in that there were significant (P ≤ 0.05) inverse correlations between Phomopsis spp. incidence and percentage seed germination, C. kikuchii incidence and percentage seed germination, and C. kikuchii incidence and oil concentration. A significant (P ≤ 0.05) inverse relationship between Phomopsis spp. incidence and C. kikuchii incidence was also detected.
  
  
  
• 2002: Mueller, D. S., Hartman, G. L., Nelson, R. L., and Pedersen, W. L. 2002. Evaluation of Glycine max germplasm for resistance to Fusarium solani f. sp. glycines. Plant Disease 86:741-746. [download] [view abstract]
  Sudden death syndrome, caused by Fusarium solani f. sp. glycines, has caused increased losses in soybean production in recent years. This study was done to identify potential sources of sudden death syndrome resistance. Over 6000 soybean plant introductions (PIs) were compared to a susceptible check, Great Lakes 3302, and two moderately resistant checks, PI 520.733 and PI 567.374. Only 60 PIs had foliar disease ratings equal to or lower than (P<0.05) PI 520.733 and PI 567.374 three weeks after inoculation. Also, 14 PIs had significantly lower disease severity ratings than PI 520.733 and six PIs had lower ratings than PI 567.374 four weeks after inoculation. Lesion lengths were measured four weeks after inoculation and ranged from 25.2 to 41.5 mm for all the PIs. None of the accessions had smaller lesions lengths than the susceptible check Great Lakes 3302. The correlation between lesion length and disease foliar severity rating was not significant. There also was no plant morphological characteristic associated with higher sudden death syndrome foliar symptoms. Eighteen moderately resistant PIs with differing agronomic traits were inoculated with five different isolates of Fusarium solani f. sp. glycines. There was very little variation for foliar symptoms among PIs within each isolate. However, there was variation for symptom intensity among isolates. Isolate Mont-1 caused the greatest disease severity ratings.
  
  
  
• 2002: Mueller, D. S., Dorrance, A. E., Derksen, R., Ozkan, E., Grau, C. R., Gaska, J. M., Kurle, J. E., Hartman, G. L., Bradley, C. A., and Pedersen, W. L. 2002. Efficacy of fungicides on Sclerotinia sclerotiorum and their potential control of Sclertoinia stem rot on soybean. Plant Disease 86:26-31. [download] [view abstract]
  Sclerotinia stem rot (SSR) of soybeans, caused by Sclerotinia sclerotiorum, is a major disease in north central growing regions of the United States. One approach to control SSR on soybeans is with the use of fungicides. Azoxystrobin, benomyl, tebuconazole, thiophanate methyl, and vinclozolin were tested to control S. sclerotiorum in pure cultures on agar medium, inoculated soybean seedlings, detached inoculated leaves, and in the field. To evaluate the efficacy of five foliar fungicides in vitro, potato dextrose agar (PDA) was amended with different concentrations of fungicide and fungal radial growth in culture was measured. Vinclozolin was the most effective in controlling S. sclerotiorum by inhibiting mycelial growth at 1.0 ug a.i./ml. Mean mycelial growth of 91 isolates of S. sclerotiorum in the thiophanate methyl and vinclozolin amended agar was reduced 18-93% and 93-99%, respectively. Greenhouse grown seedlings treated with benomyl, thiophanate methyl, and vinclozolin prevented S. sclerotiorum from colonizing leaf tissue. Azoxystrobin and tebuconazole significantly (P<0.01) reduced disease severity ratings, but did not provide complete control. Detached leaves sprayed with thiophanate methyl and then inoculated with mycelial plugs of S. sclerotiorum did not become infected, and the area under disease progress curve was significantly less (P<0.01) than the nontreated control for leaves treated with azoxystrobin, benomyl, and tebuconazole. In field plots in 1997 and 1999, all plots had less than 1% disease, while in 1998, all fungicide treated plots had similar levels of disease as the nontreated control.
  
  
  
• 2002: Hoffman, D. D., Diers, B. W., Hartman, G. L., Nickell, C. D., Nelson, R. L., Pedersen, W. L., Cober, E. R., Dorrance, A. E., Graef, G. L., Steadman, J. R., Grau, C. R., Nelson, B. D., del Rio, L. E., Helms, T., Poysa, V., Rajcan, I., and Stienstra, W. C. 2002. Selected soybean plant introductions with partial resistance to Sclerotinia sclerotiorum. Plant Disease 86:971-980. [download] [view abstract]
  Sclerotinia stem rott caused by Sclerotinia sclemtiarum, is a major soybean (Glycine max) disease in north-central regions of the United States and throughout the world. Current sources of resistance to Sclerotinia stem rot express partial resistance, and are limited in number within soybean germ plasm. A total of 6,520 maturity group (MG) 0 to IV plant introductions (PIs) were evaluated for Sclerotinia stem rot resistance in the United States and Canada in small plots or in the greenhouse from 1995 to 1997. Selected PIs with the most resistance were evaluated for resistance in the United States and Canada in replicated large plots from 1998 to 2000. The PIs in the MG I to III tests in Urbanar IL were evaluated for agronomic traits from 1998 to 2000. The selected PIs also were evaluated with an excised leaf inoculation and petiole inoculation technique. After the 1995 to 1997 evaluations, all but 68 PIs were eliminated because of their susceptibility to Sclerotinia stem rot. In field tests in Urbana, higher disease severity in selected MG I to III PIs was significantly (P < 0,05) associated with taller plant heights and greater canopy closure. All other agronomic traits evaluated were not associated or were inconsistently associated with desease severity. MG I to III PIs 153.282, 189.931, 196.157, 398.637, 417.201, 423.818, and 561.331 had high levels of resistance and had canopies similar to the resistant checks. The resistance ratings from the petiole inoculation technique had a high and significant (P < 0.01) correlation with disease severity in the MG I and II field tests. The partially resistant PIs identified in this study can be valuable in incorporating Sclerotinia stem rot resistance into elite germplasm.
  
  
  
• 2002: Mueller, D. S., Li, S., Hartman, G. L., and Pedersen, W. L. 2002. Use of aeroponic chambers and grafting to study partial resistance to Fusarium solani f. sp. glycines in soybean. Plant Disease 86:1223-1226. [download] [view abstract]
  Several plant introductions (PIs) and cultivars have been classified as partially resistant (PR) to sudden death syndrome. However, little is known about the nature of resistance to this disease. Seedlings of two PR PIs and two susceptible cultivars were inoculated with Fusarium solani f. sp. glycines in aeroponic chambers. Plants were inoculated by taping two sorghum seeds infested with F. solani f. sp. glycines to the main root. Foliar symptoms of the susceptible cultivars were higher than those on the PR PIs and were associated with lower root and plant dry weight. Root lesion lengths of the four soybean lines differed (P < 0.05), but did not correlate with foliar disease or any other variable. To better understand the resistance mechanism by distinguishing between root and plant resistance, three partially resistant PIs (PI 520.733, PI 567.374, and PI 567.650B) and one susceptible soybean cultivar (GL3302) were compared using different grafting combinations in aeroponic chambers. Results of sudden death syndrome evaluation indicated that resistance is conditioned by both the scion and the rootstock. All three PIs evaluated had resistance associated with the scion; resistance in PI 567.650B also was associated with the rootstock. Although the PR PIs used appear to have little or no root resistance, an aeroponic system and grafting may help identify new sources of resistance to F. solani f. sp. glycines with root- or whole-plant resistance.
  
  
  
• 2001: Bradley, C. A., Hartman, G. L., Nelson, R. L., Mueller, D. S., and Pedersen, W. L. 2001. Response of ancestral soybean lines and commercial cultivars to Rhizoctonia root and hypocotyl rot. Plant Disease 85:1091-1095. [download] [view abstract]
  Rhizoctonia root and hypocotyl rot is a common disease of soybean caused by Rhizoctonia solani. There are no commercial cultivars marketed as resistant to Rhizoctonia root and hypocotyl rot, and only a few sources of partial resistance to this disease have been reported. Ninety ancestral soybean lines, maturity groups (MGs) 000 to X, and 700 commercial cultivars, MGs II to IV, were evaluated for resistance to R. solani under greenhouse conditions. Most of the ancestral lines and cultivars evaluated were susceptible; however, 21 of the ancestral lines and 20 of the commercial cultivars were partially resistant. Of the 21 ancestral lines, CNS, Mandarin (Ottawa), and Jackson are in the pedigree of cultivars previously reported as being partially resistant to R. solani. In an additional study, dry root weights of 21 soybean cultivars were evaluated after inoculation with R. solani. Variation in dry root weight occurred among cultivars, but there was not a significant (P = 0.05) correlation between dry root weight and disease severity.
  
  
  
• 2001: Li, S., Bradley, C. A., Hartman, G. L., and Pedersen, W. L. 2001. First report of Phomopsis longicolla from velvetleaf causing stem lesions on inoculated soybean and velvetleaf plants. Plant Disease 85:1031. [download]
  
  
• 2001: Gardner, M. E., T. Hymowitz, S.J. Xu, and G. L. Hartman. 2001. Physical map location of the Rps1-k allele in soybean. Crop Science 41:1435-1438. [download] [view abstract]
  Several genetic maps of the soybean have been developed during the past decade. Different markers have been used to construct these maps including RFLP, AFLP, RAPD, SSR, and classical markers. However, virtually none of the maps and linkage groups developed has been associated with specific soybean chromosomes. For example, there are 13 single dominant resistance genes at 7 different loci that control Phytophthora sojae. These resistance genes (Rps genes) have not been located on any chromosomes, but several have been associated on classical and molecular maps. For example, the Rps1 locus is associated with molecular linkage group N. The objective of this study was to locate the Rps1 locus on a specific soybean chromosome using primary trisomic analysis. Crosses were made between 10 soybean trisomic lines and cv. Resnik (containing Rps1-k). The F₂ populations from trisomic parents were inoculated with race 3 of P. sojae to determine the ratio of resistant to susceptible plants. Nine of the F₂ populations tested segregated in a normal 3:1 ratio. The F₂ population of triplo 3 segregated in a 2:1 ratio, the expected segregation ratio for a single dominant gene if the gene is located on the extra chromosome, suggesting that the Rps1 locus is on chromosome 3. Thus, chromosome 3 corresponds to molecular linkage group N of the integrated genetic linkage map.
  
  
  
• 2001: Gravert, C. E., Li, S., and Hartman, G. L. 2001. Occurrence of Diaporthe phaseolorum var. meridionalis on soybean in Illinois. Plant Disease 85:1211. [download] [view abstract]
  Both Diaporthe phaseolorum var. caulivora (DPC) and D. p. var. meridionalis (DPM) cause stem canker on soybean with DPC reported in the northern regions and DPM in the southern regions of the U.S. During the 1999 and 2000 growing season, fungi were isolated from soybean plants from growers' fields exhibiting stem canker symptoms. Stem tissue along the margin of the canker was cut into 1-5 mm3 pieces, surface disinfected for 4 min in 0.5% NaOCl solution, rinsed twice, and plated on water or potato dextrose agar (PDA). Fungi of interest were hyphal tipped, grown on PDA at 21∞C with 24-hour light, and identified by culture and spore morphology after 3 to 4 weeks. Typical DPM isolates produced white, lanose colonies that turned tan with age. Most of the DPM isolates produced pycnidia with alpha spores and beaked perithecia after 25-30 days. Brown to black stroma formed in irregular shapes. Of the 16 DPM isolates identified, 11 were from Illinois, one each from Indiana and Ohio, and three each from Kentucky. In Illinois, four isolates were from the northern part of the state, the rest were from central and southern Illinois. In addition to DPM, other isolates were obtained from soybean plants including DPC, D. p. var. sojae, and Phomopsis longicolla. To date, this is the first report of DPM on soybean in Illinois.
  
  
  
• 2001: Hartman, G. L., Domier, L. L., Wax, L. M., Helm, C. G., Onstad, D. W., Shaw, J. T., Solter, L. F., Voegtlin, D. J., D'Arcy, C. J., Gray, M. E., Steffey, K. L., Isard, S. A., and Orwick, P. L. 2001. Occurrence and distribution of Aphis glycines on soybeans in Illinois in 2000 and its potential control. Plant Health Progess:(On-line). [download]
  
  
• 2000: Li, S., Hartman, G. L., Lee, B. S., and Widholm, J. W. 2000. Identification of a stress-induced protein in stem exudates of soybean seedlings root-infected with Fusarium solani f. sp glycines. Plant Physiology and Biochemistry 38:803-809. [link] [view abstract]
  Sudden death syndrome of soybean (Glycine max) is caused by the soilborne fungus, Fusarium solani f. sp. glycines, that infects soybean roots. Besides root necrosis, symptoms include interveinal leaf chlorosis, necrosis and premature defoliation. It is proposed that a fungal toxin is produced in soybean roots and translocated to foliage. In this study, we isolated compounds from soybean stem exudates from plants that were either inoculated or not inoculated with F. solani f. sp. glycines. A protein with an estimated molecular mass of 17 kDa and designated as FISP 17 for F. solani f. sp. glycines-induced stress protein was identified using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This protein occurred only in F. solani f. sp. glycines-infected soybean stem exudates. The N-terminal amino acid sequence of the purified protein had 100 % identity with a starvation-associated message 22 protein, and 80 and 78 % identity with purified bean pathogenesis-related proteins, PvPR1 and PvPR2, respectively. To determine if the protein was of plant or fungal origin, a synthetic peptide was designed based on the N-terminal sequence and used to raise a polyclonal antibody from rabbit. Western blot analysis showed that the antibody only reacted with a 17-kDa protein in F. solani f. so. glycines-infected plant exudates, but no reaction occurred with healthy plant exudates or with culture filtrates of F. solani f. Sp. glycines. This is the first report of the presence of a stress-induced protein in stem exudates of soybean seedlings root-infected with F. solani f. sp. glycines.
  
  
  
• 2000: Li, S., and Hartman, G. L. 2000. First report of Stachybotrys chartarum causing soybean root rot. Plant Disease 84:100. [download] [view abstract]
  Stachybotrys chartarum (Ehrenb. ex Link) Hughes was isolated from surface-disinfested soybean [Glycine max (L.) Merr] root lesions. The fungus was cultured on potato dextrose agar and the morphology was examined using light and an environmental scanning electron microscopy. Conidiophores were determinate, macronematous, solitary or in groups, and simple or irregularly branched. The phialides occurred in whorls and were obovate or ellipsoidal. Conidia were unicellular, round or ellipsoidal, 5-13 x 4-7 mm, initially hyaline, smooth-walled, then turning dark brown to black and rough-walled when mature. A pure culture obtained from infected soybean roots was used to test pathogenicity under greenhouse and growth chamber conditions. S. chartarum was grown on sterilized sorghum grain for 2 weeks and placed in soil 2 to 3 cm below sown soybean seeds. Non-infested sorghum grain was used as a control. All soybean plants inoculated with S. chartarum had root-rot symptoms with lesions ranging from 7 to 25 mm 21 days after sowing, while control plants did not have any measurable root rot. The DNA sequence of the ITS region was 100% identical to the S. chartarum strain ATCC 9182 (1), but differed from all published sequences of other Stachybotrys and Memnoniella species in GenBank (1). PCR using the S. chartarum-specific primer StacR3 and IT51 (1) amplified a 198-bp DNA fragment from the total genomic DNA. This molecular evidence further supports the identification of S. chartarum isolated from soybean. This is the first report of S. chartarum causing soybean root rot.
  
  
  
• 2000: Kim, H. S., Hartman, G. L., Manandhar, J. B., Graef, G. L., Steadman, J. R., and Diers, B. W. 2000. Reaction of soybean cultivars to Sclerotinia stem rot in field, greenhouse, and laboratory evaluations. Crop Sci. 40:665-669. [download] [view abstract]
  Sclerotinia stem rot of soybean [Glycine max (L.) Merr.], caused by the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, recently has increased in importance in the northern U.S. soybean production area. The objective of our study was to determine the effectiveness of three different inoculation techniques in predicting the field reactions of cultivars to sclerotinia stem rot. Eighteen soybean cultivars were field tested in six Michigan environments from 1994 to 1996 and tested in the greenhouse or laboratory with three inoculation methods. The cultivars were inoculated by placing infested oat (Avena sativa L.) seed or mycelial plugs on cotyledons or by placing mycelial plugs on detached leaves. There were significant (P < 0.05) differences in resistance to sclerotinia stem rot among cultivars at all but one field environment and for all inoculation methods. The disease severity ratings based on the inoculations were significantly correlated with the field results, with the exception of one method. Disease severity ratings for the three inoculation methods were significantly correlated with only two exceptions. Cultivars such as Novartis S19-90 and Corsoy 79 consistently had the lowest disease severity ratings in the field tests and for the inoculation methods. Similarly, a number of cultivars were rated as susceptible in all tests. Ratings for cultivars with intermediate reactions were not consistent across tests. The inoculation methods tested can provide some useful information on the resistance of soybean genotypes to sclerotinia stem rot. However, resistance identified by inoculation methods should be confirmed with field tests, since these methods can misclassify the resistance of some cultivars.
  
  
  
• 2000: Hartman, G. L., Gardner, M. E., Hymowitz, T., and Naidoo, G. C. 2000. Evaluation of perennial Glycine species for resistance to soybean fungal pathogens that cause Sclerotinia stem rot and sudden death syndrome. Crop Sci. 40:545-549. [download] [view abstract]
  The cultivated soybean [Glycine max (L.) Merr.] has a relatively narrow genetic base and most commercial cultivars are susceptible to Sclerotinia sclerotiorum (Lib.) de Bary and Fusarium solani (Mart.) Sacc. f. sp. glycines, which, respectively cause Sclerotinia stem rot (SSR) and sudden death syndrome (SDS). The objective of this study was to screen all the available accessions of the perennial Glycine species for resistance to the pathogens that cause SSR and SDS. For SSR evaluations, five seedlings of each of 787 accessions were screened once in a series of eight non-replicated runs. Seedlings were inoculated with an agar plug cut from the edge of a 1-d-old fungal culture by placing the plug next to the stem. Of the 787 accessions, 183 had partial resistance with 144 of these accessions being G. tabacina (Labill.) Benth. A selected set of 53 accessions was further screened in two replicated trials with five plants per each of four replications. Glycine tabacina had several accessions that were consistently rated as partially resistant. For SDS evaluations, five plants of each of 767 accessions were screened once in a series of eight runs. Plants were inoculated by a layered technique in which infested sorghum seed were placed below the transplanted seedlings. In the initial evaluation of 767 accessions, 134 had partial resistance with 65 of these accessions being G. tomentella Hayata. In a replicated set of selected accessions, G. tomentella had several accessions that were consistently rated as partially resistant. These perennial Glycine species represent potential untapped sources for improving disease resistance in soybean.
  
  
  
• 2000: Leitz, R. A., Hartman, G. L., Pedersen, W. L., and Nickell, C. D. 2000. Races of Phytophthora sojae on soybean in Illinois. Plant Disease 84:487. [download] [view abstract]
  Phytophthora root rot, caused by Phytophthora sojae, is a very destructive disease of soybean. Races of P. sojae have been identified from Indiana, Iowa, Ohio, and other states that are not controlled by the commonly used race-specific resistance genes in soybean. The prevalent races of P. sojae in Illinois are not known. The objectives of this study were to isolate and identify races of P. sojae in the state of Illinois. Thirty-three isolates were obtained from 192 soil samples collected throughout Illinois in 1997 and were identified to race by inoculating Rps isolines of the soybean cultivar Williams. Most P. sojae isolates were races 1, 3, 4, or variants with the addition of Rps1d virulence. One new race, 54, with virulence on the Rps1d and Rps7 alleles, accounted for 50% of the isolates. Another new race, 55, also was identified in one sample. Two isolates were obtained from plants with race-specific resistance and were virulent on those resistance alleles, and were identified as races 41 and 43. Many of the isolates were obtained from the east-central part of the state. Combining currently used resistance alleles with alleles at other loci could potentially control P. sojae in Illinois.
  
  
  
• 2000: Li, S., Tam, Y. K., and Hartman, G. L. 2000. Molecular differentiation of Fusarium solani f. sp glycines from other F. solani based on mitochondrial small subunit rDNA sequences. Phytopathology 90:491-497. [download] [view abstract]
  Fusarium solani is a soilborne plant pathogen that infects many different hosts. Within the species, there is some specialization, and a number of forma specialis have been described based on host affiliation. One of these, F. solani f. sp. glycines, infects soybean and causes sudden death syndrome. To differentiate between F. solani f. sp. glycines and other F. solani isolates, a partial sequence of the mitochondrial small subunit (mtSSU) rRNA gene was amplified by polymerase chain reaction and sequenced from 14 F. solani f. sp. glycines and 24 F. solani isolates from various plant hosts. All F. solani f. sp. glycines isolates had identical sequences. A single, unique insertion of cytosine occurred in all F. solani isolates but not in any of the F. solani f. sp. glycines isolates. Two major lineages, distinguished by sequence divergence and the presence or absence of multiple insertions, occurred in F. solani isolates. Cladistic analysis produced a single most-parsimonious tree with three major clades. The first clade contained all F. solani f. sp. glycines isolates. A second clade grouped together all of the F. solani isolates that had only a single nucleotide insertion difference from the first clade. Genetic distance between these two clades was 0.016. A third clade was formed by five F. solani isolates that had multiple insertions. Isolates in the third clade had a genetic distance of 0.040 from the first and second clades. Based on the sequence data, it is likely that F. solani f. sp. glycines has a shorter evolutionary history than other F. solani isolates that have either single or multiple nucleotide insertions. The differences in nucleotide insertions in part of the mtSSU rRNA gene between F. solani f. sp. glycines and other F. solani isolates provide a direct and reliable way to distinguish isolates off solani.
  
  
  
• 1999: Sinclair, J. B., and Hartman, G. L. 1999. Soybean rust. Pages 25-6 in: Compendium of Soybean Diseases, G. L. Hartman, et al., eds. American Phytopathological Society, St. Paul, MN. [ISBN: 0890542384] [link]
  
  
• 1999: Li, S., Hartman, G. L., and Widholm, J. M. 1999. Viability staining of soybean suspension-cultured cells and a seedling stem cutting assay to evaluate phytotoxicity of Fusarium solani f. sp. glycines culture filtrates. Plant Cell Reports 18:375-380. [link] [view abstract]
  The phytotoxicity of culture filtrates of Fusarium solani f. sp. glycines, the fungus causing sudden death syndrome (SDS) of soybean (Glycine max), was tested with a viability stain of soybean suspension-cultured cells and a stem cutting assay of soybean seedlings. Suspension-cultured cells from a SDS-susceptible soybean cultivar were exposed to cell-free culture filtrates of F. solani f. sp. glycines or other F. solani isolates for 2, 4, 6, and 8 days and then stained with 0.1% phenosafranin. The percentage of dead soybean suspension-cultured cells was greater (P < 0.001) with filtrates prepared from F. solani f. sp. glycines than from other F. solani isolates, and dead cells increased over time and with higher concentrations of culture filtrate. Cuttings of soybean seedlings with their stems immersed in culture filtrates of F. solani f. sp. glycines isolates developed SDS-like foliar symptoms, but not when immersed in filtrates of other isolates. There was a positive correlation (r = 0.94, P < 0.001) between soybean foliar symptom severity and percentage of stained soybean suspension-cultured cells. Both methods were used to determine the phytotoxicity of fungal culture filtrates.
  
  
  
• 1999: Mueller, D. S., Hartman, G. L., and Pedersen, W. L. 1999. Development of sclerotia and apothecia of Sclerotinia sclerotiorum from infected soybean seed and its control by fungicide seed treatment. Plant Disease 83:1113-1115. [download] [view abstract]
  Seed coats were removed from soybean seeds infected with Sclerotinia sclerotiorum and the seed coats and cotyledons were surface sterilized with NaOCl (0.53%), rinsed in sterile distilled water, and placed on water agar. After 48 hours, mycelia of S. sclerotiorum were observed on both seed coats and cotyledons. Infected soybean seeds also were placed in aluminum pans containing field soil and placed in soybean fields near Urbana, IL and Clinton, WI. In 1997, a total of 553 sclerotia, 20 stipes, and 10 apothecia were produced from 500 infected seeds. In 1998, 201 sclerotia, and 22 stipes were produced, but no apothecia were observed from the 500 infected seeds. Fludioxonil was the most effective fungicide for reducing radial growth of S. sclerotiorum on PDA plates and suppressed 99% of the radial growth at 0.1 ug a.i./ml. When seed lots containing infected seeds were treated with several fungicides, captan + pentachloronitrobenzene + thiabendazole and fludioxonil completely inhibited mycelial growth from infected seeds; thiram and thiabendazole reduced infection by 90%. In a similar study in the field, thiram, fludioxonil, and captan + pentachloronitrobenzene + thiabendazole reduced sclerotia formation from infected seeds by more than 98%.
  
  
  
• 1998: Huang, Y. H., and Hartman, G. L. 1998. Reaction of selected soybean genotypes to isolates of Fusarium solani f. sp. glycines and their culture filtrates. Plant Disease 82:999-1002. [download] [view abstract]
  Four soybean plant introductions, PI 520.733, PI 567.374, PI 567.650B, and PI 567.659, and one soybean cultivar, Great Lakes 3202, were inoculated under greenhouse conditions with four isolates of Fusarium solani f. sp. glycines. Foliar disease severity rating was greatest on PI 567.659, followed by Great Lakes 3202, PI 520.733, PI 567.650B, and PI567.374. There was no significant interaction between isolates and soybean entries for foliar disease severity ratings. Experiments also were conducted to determine if disease development and root colonization differed among entries. Root infection of the five entries did not differ (P = 0.05). Foliar disease progress curves increased faster for PI 567.659 and Great Lakes 3202 than for PI 567.374. The area under the disease progress curve (AUDPC) value for PI 567.374 was the lowest and differed (P = 0.01) from AUDPC values for Great Lakes 3202 and PI 567.659. There were no differences (P = 0.01) in length of taproot lesions, losses in root dry weight, and vascular stem length discoloration among the entries, and there was no correlation (P = 0.05) between these measurements and foliar AUDPC values. Cut seedling stems immersed in culture filtrate developed interveinal chlorosis on leaves of each entry within 2 days. Disease severity on cut seedlings of PI 567.374 was lower (P = 0.01) than on the other entries. There was a positive correlation (r = 0.94, P = 0.05) between AUDPC values of the five entries inoculated with the fungus and the cut seedling test using culture filtrate.
  
  
  
• 1998: Hartman, G. L., Kull, L., and Huang, Y. H. 1998. Occurrence of Sclerotinia sclerotiorum in soybean fields in East-Central Illinois and enumeration of inocula in soybean seed lots. Plant Disease 82:560-564. [download] [view abstract]
  Sclerotinia stem rot (SSR) of soybean is an important disease in the northern soybean-production areas of the United States. In Illinois, the occurrence of SSR has been limited to the northern-most soybean-production areas. In this study, soybean fields in east-central Illinois were surveyed for incidence of SSR. Of 68 fields surveyed, 31 contained SSR. Of the fields with SSR, 25 had between 1 and 5% SSR incidence, while 6 fields had more than 5% SSR incidence. The pattern of the disease in one field was mapped, and the spatial distribution of SSR was aggregated with a Lloyd's index of 1.4. In addition to field incidence of SSR, seed lots suspected of being contaminated with Sclerotinia sclerotiorum sclerotia were obtained from the Illinois Crop Improvement Association. Sclerotia and seeds were separated, and seeds were germinated to determine the level of seedborne infection by S. sclerotiorum. Sclerotia were recovered from 71 of 81 seed lots. Most of the seed lots were from the north-central area of Illinois, but one seed lot was from Madison County in the southwestern area of the state, and three and six seed lots contaminated with sclerotia were from Iowa and Wisconsin, respectively. Sclerotia counts ranged from 0 to 363 per seed lot. Normal-appearing seeds from the 81 seed lots (100 to 200 seeds per lot) were tested for germination and incidence of seedborne infection by S. sclerotiorum. Eight seed lots had at least one infected seed, and the incidence of seed infection ranged from 0.07 to 0.1%. From 10 randomly selected seed lots of the 81, discolored, shriveled seeds were selected and germinated to determine the incidence of seedborne infection. Seed infection rates ranged from 0. to 70%. The occurrence of SSR throughout Illinois and the importance of seedborne infection as a source of inoculum dispersal need further documentation.
  
  
  
• 1998: Hoffman, D. D., Hartman, G. L., Mueller, D. S., Leitz, R. A., Nickell, C. D., and Pedersen, W. L. 1998. Yield and seed quality of soybean cultivars infected with Sclerotinia sclerotiorum. Plant Disease 82:826-829. [download] [view abstract]
  Sclerotinia stem rot (SSR) is one of the most important diseases of soybean in the United States. Five maturity group III cultivars, Asgrow A3304 STS (A3304), Pioneer Brand 9342 (P9342), Pioneer Brand 9381 (P938l), Probst, and Yale, grown in fields in east-central Illinois, were used to determine the relationship of SSR incidence to yield, 100-seed weight, seed protein and oil content, visual seed quality, and seed germination. In addition, the number of sclerotia in seed samples and the seedborne incidence of Sclerotinia sclerotiorum were determined. For each cultivar, at least 23 two-row plots, 3 m long, that represented a range of SSR incidence from low to high, were used to count the number of plants with and without SSR stem symptoms and were used to estimate yields and evaluate seed quality. Disease incidence ranged from 2 to 45% for Probst, 0 to 65% for P938l, 0 to 68% for P9342, 1 to 93% for Yale, and 0 to 95% for A3304. Regression of yields on SSR incidences for each cultivar was significant (P < 0.05); for every 10% increase in SSR incidence, yields were reduced by 147, 194, 203, 254, and 263 kg/ha for Probst, A3304, P9342, Yale, and P9381, respectively. Disease incidence was negatively correlated (P < 0.05) with seed germination for all cultivars but Probst, and to oil content and seed weight for P9381 and Yale. Disease incidence was positively correlated (P < 0.05) with seed quality for all cultivars and to the number of sclerotia in harvested seeds for P9342, P9381, and Probst. The seedborne incidence of S. sclerotiorum was 0.3, 0.3, 0.3, 0.4 and 0.7% in A3304, P9381, Yale, Probst, and P9342, respectively, and represents a significant potential for further spread of this pathogen and disease.
  
  
  
• 1998: Li, S., Hartman, G. L., and Gray, L. E. 1998. Chlamydospore formation, production, and nuclear status in Fusarium solani f. sp. glycines soybean sudden death syndrome-causing isolates. Mycologia 90:414-21. [download] [view abstract]
  Six isolates of Fusarium solani f. sp. glycines, that cause soybean sudden death syndrome were examined for chlamydospore formation, production, and nuclear status, Chlamydospores formed from macroconidia either terminally, laterally by outward protrusion, or intercalarily. They also formed from germinated macroconidia and hyphae. Occasionally, a single macroconidium produced more than one chlamydospore. The percentage of chlamydospores produced differed significantly (P < 0.0001) by incubation temperature and varied among fungal isolates. More Chlamydospores formed at 30°C followed by 25°C, 20°C and 4°C. Nuclear stained Chlamydospores usually were uninucleate but occasionally multinucleate. Nuclei migrated from macroconidia into Chlamydospores through germ tubes.
  
  
  
• 1997: Pazdernik, D. L., Hartman, G. L., Huang, Y. H., and Hymowitz, T. 1997. A greenhouse technique for assessing Phytophthora root rot resistance in Glycine max and Glycine soja. Plant Disease 81:1112-1114. [download] [view abstract]
  New sources of soybean (Glycine max) resistance to Phytophthora sojae are needed to provide effective resistance because of the rapidly changing race patterns of P. sojae in fields. The objectives of our study were to develop a method to screen Glycine soja for resistance to P. sojae and then use this methodology to screen G. soja lines for resistance to P. sojae races 1, 3, and 20. An agar plug-inoculation method, in which a 3-mm-diameter mycelial plug of the fungus was placed mycelium side down on cotyledons of 10-day-old soybean seedlings, was directly compared with the traditional hypocotyl inoculation method. There was no significant difference between the hypocotyl- and plug-inoculation methods when tested on four soybean differential lines using three P. sojae races. The plug-inoculation method then was used to screen 430 G. soja accessions for resistance to P. sojae race 3. Nine G. soja accessions were retested with races 1, 3, and 20. Of the 430 G. soja accessions tested, 22 accessions had survival rates higher than 75% and nine had rates higher than 90% against race 3. Additionally, five of the nine accessions that were tested again had greater than 60% survival against races 1, 3, and 20. These results suggest that the plug-inoculation method can be used as an alternative to the hypocotyl-inoculation method. Potential sources of new P. sojae resistance and/or tolerance may be present in G. soja, but additional genetic research is needed to determine if these sources are different from sources currently found in G. max.
  
  
  
• 1997: Hartman, G. L., Huang, Y. H., Nelson, R. L., and Noel, G. R. 1997. Germplasm evaluation of Glycine max for resistance to Fusarium solani, the causal organism of sudden death syndrome. Plant Disease 81:515-518. [download] [view abstract]
  Sudden death syndrome (SDS) is an important soybean disease that potentially can be controlled by host plant resistance. In this study, over 800 soybean plant introductions (PIs), lines, and cultivars were screened for resistance to Fusarium solani. Of 728 PIs from China, PI 567.374 had mean foliar SDS severities significantly (P = 0.05) lower than PI 520.733 (resistant check) in both growth-chamber and greenhouse tests. In addition, PIs 567.315, 567.441C, 567.650B, and 567.664 had mean SDS severity ratings significantly (P = 0.05) lower than PI 520.733 in a growth-chamber test. Of 16 soybean cyst nematode-resistant entries tested, 5 had values lower than the resistant check, PI 520.733, with cv. Hartwig significantly lower in the first trial. In trial two, no entries were lower than the resistant check, although cvs. Bell and Hartwig were not significantly different from PI 520.733. In another experiment, few soybean cultivars or experimental lines had SDS severity ratings lower than PI 520.733 in any one of three trials. Some of the newly acquired PIs from China that exhibited low foliar SDS severity ratings may provide the sources of resistance needed to develop new SDS-resistant soybean breeding lines and cultivars.
  
  
  
• 1996: Michel, V. V., Hartman, G. L., and Midmore, D. J. 1996. Effects of previous crop on soil populations of Burkholderia solanacearum, bacterial wilt, and yield of tomatoes in Taiwan. Plant Disease 80:1367-1372. [download] [view abstract]
  Three field experiments were conducted to evaluate populations of Burkholderia solanacearum and the occurrence of tomato bacterial wilt in soil left fallow, and following crops of cowpea, eggplant, and rice. Bacterial population declined after cowpea and rice, but not after eggplant. The population also declined after soil was left fallow, indicating that a suitable host plant is required to maintain the bacterial population. The area under disease progress curve (AUDPC), based on the incidence of wilted tomato plants, was significantly (P < 0.05) higher following eggplant compared with cowpea and rice for three experiments and in fallow for two of the three experiments. Yields of cowpea, eggplant, and rice were not affected by the presence of B. solanacearum in the soil; however, yields of tomato crops were significantly (P < 0.05) lower following eggplant than following rice. Under greenhouse conditions, bacterial populations decreased more when soil was cropped to rice under permanently flooded conditions.
  
  
  
• 1996: Lee, G. B., Hartman, G. L., and Lim, S. M. 1996. Brown spot severity and yield of soybeans regenerated from calli resistant to a host-specific pathotoxin produced by Septoria glycines. Plant Disease 80:408-413. [download] [view abstract]
  Regenerated soybean lines from the R(3) to R(7) generations were field-evaluated for their reactions to Septoria glycines, the brown spot pathogen, from 1991 to 1994. The regenerated lines from cvs. BSR201, Fayette, and L86P-1615 were selected from calli resistant to a host-specific pathotoxin produced by S. glycines. Selected resistant plants to the pathogen from the R, generation produced R(4) progeny that were resistant, intermediate and susceptible in their reaction to S, glycines in 1991. In 1992, 1993, and 1994 among the R(3) to R(7) generations, brown spot reaction was only intermediate and susceptible. F-3 families obtained from a cross between R(3) regenerants and BSR201 had low heritability (23%) for resistance to S. glycines. Lines in the R(5) or R(6) generation, obtained originally from plants regenerated from calli of BSR201 that had intermediate and susceptible reactions to S. glycines in 1992, and five commercial soybean cultivars were evaluated for brown spot resistance, maturity, and yield in 1993 and 1994. Area-under the disease progress curve (AUDPC), maturity, and yield varied among entries. The 10 lines selected with an intermediate reaction had lower AUDPC, matured later, and had higher yields than the nine susceptible lines. Three regenerated lines, 2728, 2733, and 2734, had significantly (P = 0.05) lower AUDPC, later maturity, and higher yields than the other regenerated lines. AUDPC was significantly (P = 0.01) negatively correlated to yield (r = -0.29), to plant height (r = -0.74) and number of nodes (r = -0.39); but positively correlated to pods having 0 seed (r = 0.44) and two seeds (r = 0.49).
  
  
  
• 1996: Adebitan, S. A., Fawole, B., and Hartman, G. L. 1996. Effect of plant spacing and cropping pattern on brown blotch (Colletotrichum truncatum) of cowpea. Tropical Agriculture 73:275-280. [download] [view abstract]
  Field studies were conducted to determine the effect of plant spacing and cropping pattern on brown blotch, caused by Colletotrichum truncatum. A greater reduction of the disease occurred on intercropped compared to monocropped cowpea [Vigna uniguiculata (L.) Walp.]. Cowpea at wider spacings (between and within rows) showed lower disease incidence and severity in both monocrop and intercrop patterns than those at closer spacings. Fewer but more marketable yields were obtained from intercropped than monocropped cowpea, and from cowpea planted at wider row-spacings than those from closer spacings.
  
  
  
• 1996: Jin, H., Hartman, G. L., Nickell, C. D., and Widholm, J. M. 1996. Characterization and purification of a phytotoxin produced by Fusarium solani, the causal agent of soybean sudden death syndrome. Phytopathology 86:277-282. [download] [view abstract]
  A phytotoxic polypeptide identified in culture filtrates of Fusarium solani, the causal agent of soybean sudden death syndrome, was heat unstable, negatively charged, absorbed by 10% charcoal, and destroyed by proteinase K. The toxicity of the culture filtrates and fractions obtained during purification was bioassayed by measuring browning of soybean calli. Purification of the phytotoxin was achieved by Sephadex G-50 gel filtration chromatography followed by ion exchange chromatography on a DE-52 column. The purified protein migrated as a single band on sodium dodecyl sulfate-polyacrylamide gels with an estimated molecular weight of 17,000. The sequence of the N-terminal 15 amino acids was determined and indicated that a peptide was present. Samples containing this single protein caused browning of soybean calli, necrosis on detached soybean cotyledons and leaves, and yellowing, curling, and drying of attached soybean cotyledons and leaves.
  
  
  
• 1996: Hartman, G. L., and Sinclair, J. B. 1996. Red leaf blotch (Dactuliochaeta glycines) of soybeans (Glycine max) and its relationship to yield. Plant Path. 45:332-343. [download] [view abstract]
  Red leaf blotch of soybeans, caused by Dactuliochaeta glycines, was evaluated on soybean plants in field plots located in Zambia. Two experiments were conducted in each of two seasons. Experiment 1 had four cultivars that were either fungicide-sprayed or not sprayed. Disease severity was greatest on leaves at the lowest nodes from early vegetative through the reproductive growth stages. Area under the disease progress curve (AUDPC) values and percentage of nodes defoliated at growth stage R5 were significantly (P = 0.05) greater in unsprayed plots for all cultivars in both seasons. Yield losses ranged from 8 to 37% while reduced seed size ranged from 21 to 29% for the four cultivars. Number of pods per plant in fungicide-sprayed plots did not differ from those in unsprayed plots. However, the number of seeds per plant and seeds per pod were significantly (P = 0.05) greater in sprayed than unsprayed plots for some cultivars. In experiment 2, cultivar Tunia was either fungicide-sprayed at different times or not sprayed. The lowest attached leaf had the most variation in the amount of disease while ratings of the most median leaf in the canopy were generally less variable. The AUDPC values calculated from the lowest attached leaf, the mean of all attached leaves, and the median attached leaf differed significantly (P = 0.05) the number of times plants were sprayed with fungicide. Defoliation and vertical incidence of red leaf blotch from lower to higher nodes were significantly (P = 0.05) reduced in fungicide-sprayed plots in one season, but not the other. One thousand-seed weight and yield differed significantly (P = 0.05) with treatment as one application of triphenyltin acetate increased yields by 18% over unsprayed plots in season 1. One thousand-seed weight and yield, regressed on the AUDPC for the median leaf in the canopy, explained 92. and 72% of the variation, respectively. [References: 19]
  
  
  
• 1996: Jin, H., Hartman, G. L., Nickell, D., and Widholm, J. M. 1996. Phytotoxicity of culture filtrate of Fusarium solani, the causal agent of sudden death syndrome of soybean. Plant Dis. 80:922-927. [download] [view abstract]
  An isolate of Fusarium solani that caused sudden death syndrome (SDS) of soybean was grown in a semidefined liquid medium. The phytotoxicity oi cell-free fungal culture filtrates was determined on soybean calli grown on tissue culture medium amended with fungal culture filtrate. The mean calli brown rating increased as culture filtrate increased in the medium. There were significant (P < 0.05) positive correlations between SDS severity from field microplot data and calli browning due to culture filtrates. Seedlings of five soybean cultivars inoculated with the fungus under greenhouse conditions had significantly (P < 0.05) different foliar severity ratings and relative plant fresh weights. Sensitivity of calli of the same five cultivars to culture filtrate also had significantly (P < 0.05) different brown ratings and relative fresh weights. Then were significant (P < 0.05) correlations between variables measured on inoculated soybean seedlings and calli sensitivity, Pathogenicity and phytotoxicity of F. solani isolates from different hosts were tested on soybean plants and calli, respectively. Isolates from hosts other than soybean did not cause SDS symptoms, and their culture filtrates had significantly lower toxicity to soybean calli than did that of soybean SDS-causing isolates.
  
  
  
• 1996: Lee, J. M., Hartman, G. L., Domier, L. L., and Bent, A. F. 1996. Identification and map location of TTR1, a single locus in Arabidopsis thaliana that confers tolerance to Tobacco ringspot nepovirus. Molecular Plant-Microbe Interaction 9:729-735. [download] [view abstract]
  The interaction between Arabidopsis and the nepovirus Tobacco ringspot virus (TRSV) was characterized. Of 97 Arabidopsis lines tested, all were susceptible when inoculated with TRSV grape strain. Even though there was systemic spread of the virus, there was a large degree of variation in symptoms as the most sensitive lines died 10 days after inoculation, while the most tolerant lines either were symptomless or developed only mild symptoms. Four lines were selected for further study based on their differential reactions to TRSV. Infected plants of line Col-0 and Col-0 gl1 flowered and produced seeds like noninfected plants, while those of lines Estland and 1155 died before producing seeds, Symptoms appeared on sensitive plants approximately 5 to 6 days after inoculation. Serological studies indicated that in mechanically inoculated seedlings, the virus, as measured by coat protein accumulation, developed at essentially the same rates and to the same levels in each of the four lines, demonstrating that differences in symptom development were not due to a suppression of virus accumulation, Two additional TRSV strains gave similar results when inoculated on the four lines. Genetic studies with these four Arabidopsis lines revealed segregation of a single incompletely dominant locus controlling tolerance to TRSV grape strain, We have designated this locus TTR1. By using SSLP and CAPS markers, TTR1 was mapped to chromosome V near the nga129 marker, Seed transmission frequency of TRSV for Col-0 and Col-0 gl1 was over 95% and their progeny from crosses all had seed transmission frequencies of over 83%, which made it possible to evaluate the segregation of TTRI in F-2 progeny from infected F-1 plants without inoculating F-2 plants, Seed transmission of TRSV will be further exploited to streamline selection of individuals for fine mapping the TTRI gene. The identification of tolerant and sensitive interactions between TRSV and A. thaliana lines provides a model system for genetic and molecular analysis of plant tolerance to virus infection.
  
  
  
• 1996: Lee, G. B., and Hartman, G. L. 1996. Reactions of Glycine species and other legumes to Septoria glycines. Plant Disease 80:90-94. [download] [view abstract]
  Thirteen genera representing 30 legume species, two weed species (Abutilon theophrasti and Cynanchum laeve), and five cultivars of soybean were inoculated with Septoria glycines in the field and/or greenhouse. Of these, 29 legume species and A. theophrasti had leaf symptoms. Only Cicer arietinum was symptomless under field and greenhouse inoculations. C. laeve was found to be infected in its natural state in the field, but symptoms could not be reproduced when it was inoculated in the greenhouse. Leaf symptoms on the legume species and A. theo¬phrasti were separated into three types. All Glycine spp. except one accession of G. tabacina (PI440994) had lesions typical of soybean brown spot. Ten legume species with green cotyle¬dons had small lesions. Six legume species and A. theophrasti had atypical symptoms. Incu¬bated leaf samples from inoculated field and greenhouse-grown plants were used to count pycnidia with cirrhi. Species with small lesions and atypical symptoms had fewer pycnidia with cirrhi than those plants with typical brown spot lesions. Septoria was isolated from leaf lesions of field-grown noninoculated A. theophrasti and C. laeve plants. These isolates were similar in culture to an isolate of 5. glycines from soybean and, like the soybean isolate, caused typical brown spot lesions on soybeans and A. theophrasti.
  
  
  
• 1996: Jin, H., Hartman, G. L., Huang, Y. H., Nickell, C. D., and Widholm, J. M. 1996. Regeneration of soybean plants from embryogenic suspension cultures treated with toxic culture filtrate of Fusarium solani and screening of regenerants for resistance. Phytopathology 86:714-718. [download] [view abstract]
  Soybean embryogenic suspension cultures established from immature cotyledons of four cultivars were selected for resistance to a toxic culture filtrate of Fusarium solani, the causal agent of sudden death syndrome (SDS) of soybean. The embryogenic cultures were challenged with the fungal culture filtrates for 1 to 2 months. Many well-developed somatic embryos formed when the toxin-selected embryogenic cultures were incubated on regeneration medium; however, only a few plants were regenerated from three cultivars, whereas 98 plants were regenerated from cv. Jack embryos. The regenerants that survived were grown to maturity to obtain more seeds for screening plants for resistance to SDS. In the first experiment, the R1 (187, first-selfed generation) and R2 (225, second-selfed generation) plants of cv. Jack regenerants, resistant line PI520.733, and cvs. Jack, Great Lakes 3202, and Ripley were inoculated with a F. solani SDS isolate and rated on a 1 to 5 scale. The regenerants had significantly (P < 0.05) lower mean disease ratings than two of the three cultivars but did not differ from PI520.733. In the second experiment, R3 plants (990 from cv. Jack and 53 from cv. Spencer) were screened for SDS resistance. The regenerants did not differ significantly from the other cultivars/lines in mean disease severity ratings, although a greater percentage of regenerants (Jack and Spencer R3 combined) had disease severity ratings of 1 and 2 than did the soybean cultivars tested but not greater than PI520.733. The regenerants with lower disease severity ratings were grown to maturity to produce more seeds that will be used to screen plants for SDS resistance and for crossing to determine how heritable and useful. the resistance is in these regenerants.
  
  
  
• 1995: Hartman, G. L. 1995. Highlights of soybean rust research at the Asian Vegetable Research and Development Center. Pages 19-28 in: Proceedings of the Soybean Rust Workshop, 9-11 Aug. 1995, J. B. Sinclair, et al., eds. College of Agricultural, Consumer, and Environmental Sciences, National Soybean Research Laboratory, Urbana, IL. [link]
  
  
• 1995: Sinclair, J. B., and Hartman, G. L., eds. 1995. Proceedings of the Soybean Rust Workshop, 9-11 Aug. 1995. Urbana, IL: National Soybean Research Laboratory. [link]
  
  
• 1995: Wang, T. C., Hartman, G. L., Hsieh, W. H., and Black, L. L. 1995. Reactions of solanaceous species to Pseudocercospora fuligena, the causal agent of tomato black leaf mold. Plant Disease 79:661-665. [download] [view abstract]
  A total of 137 accessions representing 26 species and five genera of solanaceous plants were inoculated with Pseudocercospora fuligena, the causal agent of tomato black leaf mold, under controlled conditions (growth room) and in the field. Twenty of 26 species developed symptoms after inoculation under controlled conditions. Black nightshade (Solanum nigrum) developed symptoms when inoculated under controlled conditions, but not in the field. Ground cherry (Physalis sp.), five Irish potato (Solanum tuberosum) cultivars, and eight tobacco (Nicotiana tabacum) lines remained symptomless following inoculation both under controlled conditions and in the field. Of 40 pepper accessions representing four species of Capsicum tested under controlled conditions, 32 developed lesions and eight were symptomless. Of 33 eggplant (Solanum melongena) accessions and related species representing seven Solanum spp. tested under controlled conditions, 24 developed symptoms and nine were symptomless. Two commercial eggplant cultivars, Pingtung Long and Farmers Long, were highly susceptible under controlled conditions and in the field. Among 46 Lycopersicon accessions representing 10 species that were evaluated, accessions of L. esculentum were the most susceptible and accessions of L. hirsutum were the most resistant. Five Lycopersicon spp., three Solanum spp., and four Capsicum spp. are reported as new hosts of P. fuligena.
  
  
  
• 1995: Manandhar, J. B., Hartman, G. L., and Wang, T. C. 1995. Conidial germination and appressorial formation of Colletotrichum capsici and C. gloeosporioides isolates from pepper. Plant Disease 79:361-366. [download] [view abstract]
  Conidial germination and appressorial formation of Colletotrichum capsici and C. gloeosporioides were examined on pepper fruits and in association with some inorganic and organic compounds. Conidial germination and appressorial formation were greater on immature green or ripe red fruits of pepper (Capsicum annuum) variety Long Fruit than in water droplets on glass slides. Conidial germination was significantly (P = 0.05) higher for both fungi as concentrations of either sucrose or KCl increased. Appressorial formation for C. capsici was highest when sucrose was 10 mM and for C. gloeosporioides at 0.1 mM. Appressorial formation was reduced and mycelia formed for both fungi at higher sucrose concentrations, but not at 1-100 mM of KCl. Among six compounds tested for induced conidial germination and appressorial formation, CaCl2 and sucrose caused a significant (P = 0.05) increase, KCl an intermediate one, and AlCl3 was lowest. beta-resorcilic acid did not stimulate conidial germination and appressorial formation, and Fe-resorcilic acid stimulated conidial germination only for C. capsici. Three test melanin biosynthesis inhibitors at 1 mu g per milliliter stimulated conidial germination but varied in causing appressorial formation for both fungi. Appressorial formation of C. capsici was completely inhibited by tricyclazole and stimulated by fthalide and isoprothiolane; appressorial formation of C. gloeosporioides was completely inhibited and stimulated by isoprothiolane and tricyclazole, respectively, and only slightly inhibited by fthalide. Inorganic and organic compounds that affect conidial germination and appressorial formation may play a role in the preinfection process of Colletotrichum spp. on pepper fruits.
  
  
  
• 1995: Hartman, G. L., and Huang, Y. H. 1995. Characteristics of Phytophthora infestans isolates and development of late blight on tomato in Taiwan. Plant Disease 79:849-852. [download] [view abstract]
  Thirteen isolates of Phytophthora infestans were grown on various solidified media. Growth of all isolates was best on rye A agar. Mean sporangia length and width ranged from 23.5 to 41.7 mu m x 13.9 to 23.4 mu m, respectively, with a length/width ratio of 1.69 to 1.92. All isolates were Al mating type and all isolates, except one isolate from potato, were classified race T1 because blight developed on three tomato lines with the Phl resistance gene. Area under the disease progress curve (AUDPC) differed significantly (P < 0.05) by isolate on both detached tomato leaflets and pot-cultured seedlings. Isolate Pill from potato had the lowest AUDPC values on detached leaves and seedlings. Late blight occurred on tomato seedlings transplanted monthly in the central highlands of Taiwan with greatest disease severity from March to June. Field-grown tomatoes sprayed with metalaxyl once and twice per week reduced late blight AUDPC values, decreased yield losses, and increased fruit numbers, compared with the results from fewer or no sprays. Disease, measured as AUDPC, correlated negatively (P < 0.05) to yield (r = -0.82) and number of fruit (r = -0.76).
  
  
  
• 1995: Manandhar, J. B., Hartman, G. L., and Wang, T. C. 1995. Semiselective medium for Colletotrichum gloeosporioides and occurrence of three Colletotrichum spp. on pepper plants. Plant Disease 79:376-379. [download] [view abstract]
  Inhibition of mycelial growth of Colletotrichum capsici and C. gloeosporioides was significantly (P = 0.01) less than that of Alternaria sp, and Fusarium spp. when grown on a semiselective medium, C. gloeosporioides pepper isolate medium (CGPIM) containing one-quarter strength potato-dextrose agar amended with fenarimol and vinclozolin at 5 mu g/ml each, chloramphenicol and erythromycin at 6.5 mu g/ml each, iprodione at 15 mu g/ml, neomycin sulfate at 20 mu g/ml, and tetracycline hydrochloride at 25 mu g/ml. Fenarimol enhanced the detection of C. gloeosporioides as cream-yellow sporulating colonies formed around infected and/or infested pepper (Capsicum spp.) seeds. When pepper seeds were placed on CGPIM and wet filter paper, C. capsici occurred at equal frequencies, but the frequency of C. gloeosporioides was significantly (P = 0.01) higher on CGPIM than on wet filter paper. C. capsici was detected on 14.5% of the seeds from var. LSU Sport, while C. gloeosporioides detection was less frequent. C. gloeosporioides was isolated from 30 and 1% of diseased fruits harvested and stored for 130 and 225 days, respectively. CGPIM and wet filter paper were equally effective in evaluating the occurrence of C. capsici, but the occurrence of C. gloeosporioides and Glomerella cingulata appressoria was significantly (P = 0.01) higher on CGPIM than on wet filter paper. C. capsici was recovered more frequently than either C. gloeosporioides or G. cingulata on inoculated leaves.
  
  
  
• 1995: Manandhar, J. B., Hartman, G. L., and Wang, T. C. 1995. Anthracnose development on pepper fruits inoculated with Colletotrichum gloeosporioides. Plant Disease 79:380-383. [download] [view abstract]
  Colletotrichum gloeosporioides caused anthracnose on pepper fruits of line PBC 510 when inoculated with a microdrop spore suspension on immature fruits one-half the normal size up to fully mature ripe red fruits. Incidence of anthracnose was greater on inoculated purple and ripe red fruits than on fruits at other developmental stages. Cuticle and exocarp thicknesses varied by fruit maturity. Disease incidence differed among eight pepper lines based on the number of days to fruit lesion development. Over 50% of the fruits in lines PBC 452, PBC 454, and PBC 595 had lesions less than 5 days after inoculation, whereas it took 6 days for fruits in three lines (PBC 365, PBC 371, and PBC 518), 8 days for fruits in line PBC 370, and 11 days for fruits in line PBC 495. Fruits of PBC 595 had the largest lesions, while fruits of PBC 518 had the smallest lesions. Conidial production was lowest on fruit lesions of PBC 495 and highest on fruit lesions of PBC 595. Disease incidence was correlated to cuticle and exocarp thicknesses. Cuticle thickness was significantly negatively correlated to conidial production (r = -0.45) and lesion expansion (r = -0.46). C. gloeosporioides infected more fruits of var. Szechwan 90714 in a given period than did C. capsici, whether or not fruits were chloroform-dipped. Anthracnose was detected more on incubated fruits that were chloroform-dipped than water-dipped prior to inoculation.
  
  
  
• 1995: Hartman, G. L., Noel, G. R., and Gray, L. E. 1995. Occurrence of soybean sudden death syndrome in east-central Illinois and associated yield losses. Plant Dis. 79:314-318. [download] [view abstract]
  Sudden death syndrome (SDS) of soybeans, causal organism Fusarium solani, occurred for the first time in epidemic proportions in east-central Illinois in 1993. SDS occurred in 46% of the soybean fields, based on air and ground surveys. Within fields containing plants with SDS, the percent area affected ranged from 1 to 70% with an average of 7.3 and 13.9% for ground and aerial surveys, respectively. Soil samples taken in 25 fields in areas where all plants showed SDS symptoms and in adjacent areas where plants appeared healthy did not differ in cyst populations of soybean cyst nematode (Heterodera glycines). Disease severity and yield components were compared from replicated plots at an experimental farm and in a commercial field and in a nonreplicated commercial field. Diseased plants from infested areas had fewer pods and seeds and less 300-seed weights. Plant yields were 46, 41, and 20% less for plants in plots with a high incidence of SDS than were the yields for those with a low incidence of SDS in a nonreplicated commercial field, replicated plots at an experimental farm, and a commercial field, respectively. Seed germination was less and the frequency of Phomopsis spp. was greater on seeds harvested from plants in plots with a high occurrence of SDS compared to plots with a low occurrence of SDS.
  
  
  
• 1995: Hartman, G. L., and Lee, G. B. 1995. Velvetleaf a host for Septoria glycines. Plant Disease 79:426. [download] [view abstract]
  Brown spot of soybean [Glycine max (L.) Merr.] caused by Septoria glycines, occurs in most soybean production areas as does velvetleaf (Abutilon theophrastii Medik.) (1). Leaves with lesions from soybean and velvetleaf were collected at the Agronomy/Plant Pathology South Farm in August 1993. Leaves were disinfected with 0.5 NaOCl for 2 minutes, rinsed, and incubated on sterile moist filter paper in glass dishes for 4 days. Isolates were cultured on potato dextrose agar (PDA) at 23 2 C under 24 hour fluorescent light for 15 days. Colonies on PDA were black with gobose or subglobose black pycnidia that produced hyaline slightly curved one to five septated conidia that were 9.8-37.8 m x 1.4-1.9 m from velvetleaf and 14-42 m x 1.4-2.1 m from soybean. Cross inoculations using two soybean and one velvetleaf isolate on soybean cv. Williams and velvetleaf were conducted twice in the greenhouse. Leaf lesions and pycnidia developed on both plant species but not on noninoculated control plants. Lesions on velvetleaf had irregular margins without surrounding chlorosis and were somewhat larger than the smooth-margin lesions surrounded by chlorosis found on soybean. S. glycines was reisolated from the infected leaves of both hosts, and were morphologically identical to the original isolates. This is the first report of S. glycines on a nonlegume host. Interpretive Summary: Brown spot of soybean is caused by a fungus named Septoria glycines which infects soybean leaves and occurs in most soybean production areas. The number of plants attacked by this fungus has not been documented, but it is presumed to attack only a few species of legume plants. Velvetleaf is a common weed found in soybean fields. Its origin like soybean is in Asia. There have been no previous reports that velvetleaf is a host for this soybean pathogen. The importance of this discovery includes testing this pathogen for its potential use as a biological control agent and it expands the known plant hosts attaked by this fungus which was limited to only a few legume species.
  
  
  
• 1993: Hartman, G. L., and Huang, Y. H. 1993. Pathogenicity and virulence of Phytophthora capsici isolates from Taiwan on tomato and other selected hosts. Plant Dis. 77:588-591. [download] [view abstract]
  Black nightshade, cabbage, cucumber, pepper, potato, tobacco, and tomato plants were inoculated with isolates of Phytophthora capsici obtained either from pepper stems or tomato foliage in container experiments. Inoculum was added by either atomizing foliage or drenching soil with zoospore suspensions of 1 x 104 zoospores/ml. Foliage and stem blight developed on black nightshade, pepper, and tomato plants, but not on the other plant species. Tomato and pepper seedlings were inoculated with five isolates P. capsici by either foliar-spray or soil drenching. The range of response caused by individual isolates varied from no symptoms to 100% blighting and death of pepper plants when foliar-inoculated. Regardless of isolate, basal stem blight was not observed on tomatoes that were soil-inoculated while individual isolates caused no symptoms to severe crown lesions causing pepper plants to die. Seedlings of 11 tomato lines that were foliar-inoculated with one isolate were all susceptible although there were differences in the amount of foliage blighted between lines. Detached tomato leaves inoculated with a zoospore suspension had more blight at 24 and 28 C compared to higher and lower temperatures 3 days after inoculation. In the field, two foliar-inoculated tomato lines developed leaf blight 3 days after inoculation and by 14 days, 45-60% of the leaf area was blighted. Interpretive Summary: Phytophthora capsici is a soilborne fungus that attacks many hosts. The fungus normally infects root and lower stems of plants causing them to die. The fungus occasionally attacks plant leaves, although it is not known how many host plants are infected through leaves. The objective was to compare the degree of infection on tomatoes and other selected hosts when applying the fungal pathogen to roots and leaves. Leaves and stems of black nightshade, pepper, and tomato plants, but not cabbage, cucumber, potato, and tobacco became infected. Black nightshade was recorded as a new host. When tomato leaves were infected, the symptoms resembled the symptoms of late blight of tomato caused by P. infestans., a different fungal species. This is important because it indicates that P. capsici might be an important fungus attaking leaves of tomato and leads to more questions regarding the occurrence and control of P. capsici in highland subtropical regions of the world.
  
  
  
• 1992: Hartman, G. L., Saddoui, E. M., Tschanz, A. T., MacIntyre, R., and Lopez, K., eds. 1992. Annotated Bibliography of Soybean Rust (Phakopsora pachyrhizi Syd.), AVRDC Library Bibliography Series 4-1, Tropical Vegetable Information Service. Taipei: Asian Vegetable Research and Development Center. [link]
  
  
• 1992: Wang, T. C., and Hartman, G. L. 1992. Epidemiology of soybean rust and breeding for host resistance. Plant Protection Bulletin (Taiwan) 34:109-124. [download] [view abstract]
  Soybean rust, caused by Phakopsora pachyrhizi, is a major disease limiting soybean production primarily in the tropics and subtropics of Asia. Research at the Asian Vegetable Research and Development Center (AVRDC) has focused on monitoring disease development; evaluating yield losses; obtaining basic information on the biology of the fungus; and on finding sources of resistance and developing these sources into breeding lines. Rust was monitored on one moderately resistant and three susceptible lines at five locations in Taiwan during three separate seasons. Apparent infection rates were similar within lines over locations and seasons. Several experiments showed that soybean maturation was significantly positively correlated to the rate of rust development, whereas effects due to the environment and the host genotype were not as highly correlated. To compare soybean lines, methods were developed to compensate for differences in host maturities. The best method used the relative soybean life time (RLT) as a time element from 0 to 100. The time between planting and maturity was converted to a percentage of the soybean life cycle completed. Factors related to pathogenic diversity of the fungus, and the effect of environmental parameters were studied. Nine races were identified from forty-two isolates using a differential set consisting of 11 lines. The predominant races were complex with multiple virulence factors for compatibility on the differentials. Studies on leaf wetness and temperature indicated that the optimum temperature for uredospore germination was 15~ 25°C ; the minimal dew period for infection was 6 hours at 20~ 25°C and 8-10 hours at 15~ 17.5°C ; and a mean night temperature below 15°C greatly reduced lesion numbers or completely prevented lesion development. Field studies showed that precipitation was a critical factor in the development of epidemics. It was used to predict rust severity, and was more important than frequency and intensity of the infection period which consisted of leaf wetness, temperature, and their interaction. Difficulties associated with identifying and quantifying rate-reducing resistance and the ineffectiveness of race-specific resistance have brought about techniques to develop higher soybean yields with tolerance to rust. Also techniques were developed to better quantify and understand the components involved in partial resistance. In other studies, new sources of resistance were identified in accessions of the wild perennial Glycine species. (Key words: Phakopsora pachyrhizi, infection rates, perennial Glycine spp., yield losses, races)
  
  
  
• 1992: Hartman, G. L., and Sinclair, J. B. 1992. Cultural studies on Dactuliochaeta glycines, the causal agent of red leaf blotch of soybeans. Plant Disease 76:847-52. [download] [view abstract]
  Sclerotia of Dactuliochaeta glycines were isolated from leaf lesions of soybeans (Glycine max), a wild perennial relative (Neonolonia wightii) of soybeans, and soil. Recovery of sclerotia from soybean field soil ranged from three to 19 sclerotia per gram of dry soil. More than 90% of sclerotia germinated at 5 C after 18 mo, and more than 22% germinated when incubated at 100 C for 120 min. Pycnidiospore germination was optimal at 20 and 25 C. Pycnidiospores did not germinate after incubation for 12, 24, or 36 hr at 5 or 35 C. In culture, the fungus produced sclerotia on substrates with organic nitrogen sources, oat and wheat seeds, wood, and detached leaves of some legume species. Pycnidia and sclerotia were produced abundantly on media containing asparagine or casein hydrolysate, respectively. Pycnidia did not fully develop on culture media with greater than 1% sodium chloride. Inoculated leaf disks of 10 Glycine species and six other leguminous plants were infected, and on some species, typical lesions, pycnidia, and sclerotia developed.
  
  
  
• 1992: Hartman, G. L., Wang, T. C., and Hymowitz, T. 1992. Sources of resistance to soybean rust in perennial Glycine species. Plant Disease 76:396-399. [download] [view abstract]
  Accessions of 12 perennial Glycine species were evaluated for resistance to Phakopsorapachyrhizi, the causal agent of soybean rust. A total of 23% of the accessions were resistant, 18% were moderately resistant, and 58% were susceptible. In two experiments, 59 and 40% of the accessions of G. tabacina (2/n=80) were resistant. Resistance to P. pachyrhizi was identified in accessions of G. argyrea, G. canescens, G. clandestina, G. latifolia, G. microphylla, and G. tomentella, but not in accessions of G. arenaria, G. cyrtoloba, G. curvata, and G. falcata.
  
  
  
• 1991: Hartman, G. L., Chen, S. C., and Wang, T. C. 1991. Cultural studies and pathogenicity of Pseudocercospora fuligena, the causal agent of black leaf mold of tomato. Plant Disease 75:1060-1063. [download]
  
  
• 1991: Hartman, G. L., Hong, W. F., and Wang, T. C. 1991. Survey of bacterial wilt on fresh market hybrid tomatoes in Taiwan. Plant Protection Bulletin (Taiwan) 33:197-203. [download] [view abstract]
  Bacterial wilt of tomato, caused by Pseudomonas solanacearum, is the most impor¬tant disease of tomato throughout the humid tropics. Breeding for disease resistance has been the primary means of control and a few moderately resistant hybrids are available to growers in Taiwan. In this survey, the incidence of bacterial wilt on hy¬brids averaged 15% in 11 fields and 26% in 17 fields for Hualien ASVEG No. 5 and Taichung ASVEG No. 4, respectively, whereas other hybrids averaged 55% in 16 fields. Within the same field, the population density of P. solanacearum was 34 times higher in the soil associated with roots of wilted plants than from nonwilted plants. Based upon average price per kilogram of fresh market tomatoes (June to October), the es¬timated monetary losses on the surveyed fields was NT$ 496,000/ha. (Key words: crop loss, bacterial population)
  
  
  
• 1991: Hartman, G. L., Wang, T. C., and Tschanz, A. T. 1991. Soybean rust development and the quantitative relationship between rust severity and soybean yield. Plant Disease 75:596-600. [download] [view abstract]
  Phakopsora pachyrhizi was inoculated on two soybean (Glycine max) genotypes at three different reproductive growth stages (GS) in four trials. Leaf rust was more severe on Taita Kaohsiung No. 5 (TK 5), a commercial cultivar, than on SRE-B15-A (B15 A), a genotype selected for tolerance to leaf rust. At GS R6, the percentage of leaf area infected ranged from 14 to 95% for TK 5 and from 0 to 34% for B15 A. Values for area under disease progress curve (AUDPC) were significantly greater for TK 5 than B15 A. Yields in fungicide-protected plots ranged from 2,312 to 3,546 kg/ ha and were not significantly different between the genotypes. Average yields of plants inoculated at GS Rl were reduced by 62 and 22% and seed weights by 35 and 14% for TK 5 and B15 A, respectively, compared with fungicide-protected plots. Regressions of yield percentage of fungicide-protected plants on disease severity assessments at GS R6, AUDPC, and area under the green leaf area curve were significant for both genotypes.
  
  
  
• 1991: Hartman, G. L., and Tanimonure, O. A. 1991. Seed populations of Striga species in Nigeria. Plant Disease 75:494-6. [download] [view abstract]
  Seeds of Striga asialica, S. gesnerioides, and S. hcrmonthica were separated from soil with a 2.5 M sucrose flotation solution and 250- and 150-jim mesh screens. In 34 fields, the average and range of seeds-100 g-1 of soil were 8.2 and 0-75, respectively. Seeds were recovered from 28 of the 34 fields sampled. Eighteen, six, and four fields had 1-5, 6-20, and > 21 seeds*100 g-1 of soil, respectively. The maximum number of seeds*100 g -1 of soil was 202, collected from one sample site in a field. Emerged 5. asialica, S. gesnerioides, and S. hermonthica were counted from 28 fields, and neither seeds nor plants, of Striga were counted in two fields. The average number of seeds per plant produced by S. gesnerioides was 6.4 X I04, and the average number of seeds per capsule was 604. Seed recovery and plant emergence were correlated (r = 0.79) at one site where 29 4 X 10 m plots were assessed.
  
  
  
• 1991: Hartman, G. L., and Huang, Y. H. 1991. Infection of pepper and tomato by Phytophthora capsici. Plant Dis. 75:751. [download]
  
  
• 1990: Hartman, G. L., and Wang, T. C. 1990. Soybean yield loss and rust development on a partial resistant, tolerant genotype and on a susceptible, intolerant cultivar [Abst.]. Plant Prot. Bull. Taipei 32:340. [link]
  
  
• 1990: Hartman, G. L., and Yang, C. H. 1990. Occurrence of three races of Xanthomonas campestris pv. vesicatoria on pepper and tomato in Taiwan. Plant Disease 74:252. [download]
  
  
• 1989: Bowman, J. E., Hartman, G.L., McClary, R.D., Sinclair, J.B., Hummel, J.W., and Wax, L.M. 1989. Effect of cropping sequence, row spacing, tillage and herbicide applicatioin of soybean seed quality. Seed Science and Technology 17:531-542. [download]
  
  
• 1988: Hartman, G. L., and Sinclair, J. B. 1988. Dactuliochaeta, a new genus for the fungus causing red leaf blotch of soybeans. Mycologia 80:696-706. [download] [view abstract]
  The generic name Dactuliochaeta is established to accommodate Pyrenochaeta glycines, the causal agent of red leaf blotch of soybeans and its synanamorph Dactuliophora glycines. The fungus is rede-scribed and illustrated from isolates originating from sclerotia on Neonotonia wightii or soybean (Glycine max) leaves or that were sieved from soil in Zambia, Africa. The genus is characterized by setose sclerotia which germinate to form mycelium and then setose pycnidia and/or pycnidia and sclerotia on their surfaces. The inner pycnidial walls are lined with ampulliform to lageniform, phialidic conid-iogenous cells that often are periclinally thickened at the conidiogenous locus and bear uninucleate, hyaline conidia.
  
  
  
• 1988: Manandhar, J. B., Hartman, G. L., and Sinclair, J. B. 1988. Soybean germ plasm evaluation for resistance to Colletotrichum truncatum. Plant Disease 72:56-59. [download] [view abstract]
  The number of conidia per square centimeter of potato-dextrose agar (PDA) disk produced by Colletoirichum truncatum, cause of soybean (Glycine max) anthracnose, and its pathogenicity on soybean seedlings varied among seven isolates. Isolate Ct-1 from soybeans produced more conidia than other isolates and was highly pathogenic on inoculated soybean seedlings and seeds. Foliar anthracnose in susceptible plants inoculated with a conidial suspension of isolate Ct-1 progressed curvilinearly with increased time in a mist chamber. Seedlings inoculated at the VI growth stage were killed within 72 hr. Plants inoculated at the V2, V6, and R4 growth stages were defoliated within 72 hr. Necrosis in stem tips occurred most often at V2, intermediately at V6, and least at R4 growth stages. Disease development and survival of C. truncatum in soybean cultivars remained high after 0-98 hr under dark conditions but decreased with increasing periods under light conditions. None of the 414 germ plasm accessions of maturity groups 000-X inoculated at the VI growth stage and evaluated for foliar anthracnose was immune. Several lines in maturity groups 00-IV, PI 96.860 (maturity group VI), and Tarheel Black (maturity group VII) were resistant.
  
  
  
• 1986: Manandhar, J. B., Hartman, G. L., and Sinclair, J. B. 1986. A loculate stromatic conidiomatal isolate of Glomerella cingulata. Transactions of the British Mycological Society 86:451-456. [download] [view abstract]
  An isolate of Glomerella cingulata (anamorph Colletotrichum gloeosporioid.es) which formed loculate stromatic conidiomata was recovered from a single ascospore line from soybeans (Glycine max). The loculate stromatic conidomata were formed on the surface of potato-dextrose agar and subepidermally in apple fruits. The loculi were without ostioles and broke open presumably from pressure exerted by developing conidia. Conidiogenesis and conidial morphology are similar to ascospore lines of three other acervular anamorphs of G. cingulata.
  
  
  
• 1986: Manandhar, J. B., Hartman, G. L., and Sinclair, J. B. 1986. Colletotrichum destructivum, the anamorph of Glomerella glycines. Phytopathology 76:282-285. [download] [view abstract]
  Morphology of acervuli, perithecia. conidia, and ascospores, perithecia of G. glycines, and NaCl-yeast extract agar plus sucrose for development and morphology of appressoria, and discharge of ascospores culturing the fruiting structures of both forms. Colletotrichum truncatum of Glomerella glycines were studied on soybean (Glycine max) and in did not produce the teleomorph, G. glycines, on any of the media tested. Colletotrichum destructivum was shown to be the anamorph of G. destructivum and G. glycines produced no symptoms in soybean tissues, glycines. Appressorial development and morphology are described for the but isolates from soybean pods and stems were pathogenic to soybean first time. Sodium chloride-yeast extract agar was used for culturing unifoliolate leaves in reinoculation studies, acervuli of C. destructivum, potato-dextrose agar for culturing the
  
  
  
• 1986: Hartman, G. L., Manandhar, J. B., and Sinclair, J. B. 1986. Incidence of Colletotrichum spp. on soybeans and weeds in Illinois and pathogenicity of Colletotrichum truncatum. Plant Disease 70:780-782. [download] [view abstract]
  Hartman, G. L., Manandhar, J. B., and Sinclair, J. B. 1986. Incidence of Colletotrichum spp. on soybeans and weeds in Illinois and pathogenicity of Colletotrichum truncatum. Plant Disease 70:780-782. Colletotrichum destructivum, C. truncatum, and domerella glycines occurred on 22% of stubble samples collected in 1984 and on 100% of samples from all but one of 50 fields of soybean (Glycine max) planted in 1983 in three Illinois counties. Colletotrichum spp. were recovered from 50% of soybean leaflets and from 48% of either stem pieces or leaf samples of 17 weeds from 18 fields. C. truncatum was recovered from 14 genera of weed hosts. Single-conidium isolates of C. truncatum from 11 weeds and soybeans varied significantly (P = 0.05) in pathogenicity on two soybean cultivars; one soybean isolate and four weed isolates were pathogenic on four of the weed hosts.
  
  
  
• 1986: Bowman, J. E., Hartman, G. L., McClary, R. D., and Sinclair, J. B. 1986. Effects of weed control and row spacing in conventional tillage, reduced tillage, and nontillage on soybean seed quality. Plant Disease 70:673-6. [download] [view abstract]
  In a 3-yr study on an Illinois silt loam soil, soybean (Glycine max) seed quality was not affected by tillage practices. Under conventional, reduced, and nontillage practices, seed weight, seed germination, seedling vigor, and recovery of seedborne pathogens remained the same. In individual years, seeds from plants under nontillage had significantly (P- 0.05) lower weight and recovery of Alternaria spp. and seedborne bacteria than seeds from plants under conventional tillage, except there was a higher recovery of Allernaria spp. from seeds on 25-cm than on 75-cm centers. The highest yields and most effective weed control were found consistently in the conventional tillage plots. Weed control method affected seed quality more than either tillage or row spacing. Bentazon + sethoxydim herbicide application resulted in significantly heavier seeds but less weed control than alachlor + metribu/in. Seeds from nonweeded control plots had a significantly higher incidence of Phomopsis spp. than seeds from all herbicide-treated plots under conventional and reduced tillage but not from plots under nontillage.
  
  
  
• 1985: Manandhar, J. B., Kunwar, I. K., Singh, T., Hartman, G. L., and Sinclair, J. B. 1985. Penetration and infection of soybean leaf tissues in Colletotrichum truncatum and Glomerella glycines. Phytopathology 75:704-708. [download] [view abstract]
  Conidial germination, infection peg penetration, and establishment of the anthracnose-causing fungi (Colletotrichum truncatum and Glomerella glycines) on and in soybean (Glycine max) leaf tissues, was studied by using bright-field microscopy and scanning electron microscopy. Conidial suspensions of both fungi were atomized onto soybean leaves in a mist chamber at ambient temperature (24 ± 2 C). Seventy percent of conidia of C. truncatum germinated within 4 hr; 25 and 40% of the conidia of G. glycines germinated at 6 and 12 hr, respectively. Conidia of both fungi germinated terminally and subterminally with germ tubes that developed appressoria. The germ tubes of both fungi were significantly (P = 0.05) longer when conidia germinated on midribs than on leaf laminae. One and sometimes two appressoria developed from a single germ tube of conidia of C. truncatum. Penetration of epidermal cells by infection pegs from appressoria of both fungi was common. Indirect penetration through stomatal openings or direct penetration of guard cells was rare. Hyphae were observed in and between mesophyll cells at 2 days and in the vascular elements 3 days after inoculation. Acervuli were produced by conidia of C. truncatum and G. glycines at 48 and 72 hr, respectively, and were common on leaf veins and petioles. Discrete veinal necrosis of inoculated leaves was evident only with conidia of C. truncatum at 30 hr after inoculation of plants.
  
  
  
• 1985: Cubeta, M. A., Hartman, G. L., and Sinclair, J. B. 1985. Interaction between Bacillus subtilis and fungi associated with soybean seeds. Plant Disease 69:506-9. [download] [view abstract]
  A Bacillus subtilis isolate from soybean was tested for antagonism against 26 fungi commonly associated with soybean seeds in dual culture on potato-dextrose agar (PDA) and soil-extract agar. The bacteria were fungicidal to Penicillium sp. and fungistatic to all others. Autoclaved filtrates of B. subtilis cultures inhibited growth and stroma formation of Phomopsis sp. A chloroform-soluble component from autoclaved B. subtilis culture filtrates was active against seven soybean pathogens on PDA. Suspensions of B. subtilis applied as a soybean seed treatment reduced stem infection caused by Phomopsis sp., emergence, and plant height in the field but not in greenhouse or growth chamber studies. Suspensions of B. subtilis sprayed on soybean plants significantly reduced Phomopsis pod infection in a growth chamber but not in the field.