- 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.
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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:
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.
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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:
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.
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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.
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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.
- 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.
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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.
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- 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.
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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.
- 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.
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- 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.
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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.
- 2006:
Wang, Y., Hobbs, H. A., Bowen, C. R., Bernard, R. L., Hill, C. B., Haudenshield, J. S., Domier, L. L., and Hartman, G. L. 2006. Evaluation of soybean cultivars, ‘Williams’ isogenic lines, and other selected soybean lines for resistance to two Soybean mosaic virus strains. Crop Sci. 46:2649-2653.
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Soybean mosaic virus (SMV) is one of the most common soybean viruses worldwide. The resistance or susceptibility of most commercial soybean cultivars to SMV is not known. The objectives of this study were to evaluate resistance to SMV strains G1 and G5 of current soybean cultivars, isogenic lines with different Rsv genes and alleles in ‘Williams’ or ‘Williams 82’ background, and selected soybean lines with reported or observed SMV resistance. Commercial and precommercial soybean cultivars were screened for resistance to SMV strains G1 and G5. Based on multiple tests, 1.5% and 6.7% of the 850 cultivars were resistant to SMV-G1 and SMV-G5, respectively. No cultivars were resistant to both strains. Expression of different SMV resistance genes in Williams isogenic lines inoculated with both SMV strains indicated that lines with Rsv1-y from ‘Dorman’, or unnamed resistance genes from ‘Kosamame’, and ‘Sodendaizu’, were resistant to G1 and susceptible to G5. Lines with Rsv1 alleles from PI 96983, ‘Marshall’, or ‘Ogden’ were resistant to both strains, and lines with Rsv1 alleles from ‘Raiden’, ‘SS 74185’ (PI486355), or ‘Suweon 97’ were resistant to G1 and produced a systemic necrosis reaction with G5. Lines with Rsv3-h from ‘Hardee’ were susceptible to G1 and resistant to G5. Isogenic lines with SMV resistance genes from ‘Buffalo’ showed either a resistant–resistant or resistant–susceptible reaction to the two SMV strains, suggesting the presence of more than one SMV resistance gene. Ten selected lines with reported or observed resistance to SMV were inoculated with the two SMV strains. Some lines were resistant to either G1 or G5, and some were resistant to both strains.
