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Current Research on Green Stem Disorder

Research Overview: Green stem is a disorder of soybean that causes the stems of the plants to remain immature and moist after pods and seeds have fully ripened, while the normal condition is for the stems to mature and dry down along with the pods and the seeds. Although the disorder has not been shown to affect soybean yields, it significantly increases difficulty in harvesting because green stem affected plants are much harder to cut. Green stem was first reported in Kansas in 1974 and is now widely distributed throughout all soybean-growing regions. Initially, Bean pod mottle virus (BPMV) was thought to be the cause of the disorder, however, recent work indicated that the disorder is independent of BPMV infection. Because the cause of the disorder is unknown, it is referred to as a disorder rather than a disease. Green stem disorder is currently the most common type of delayed maturity found in Illinois and Wisconsin and distinguishable from other types of delayed maturity by normal ripening of pods and seeds. There are consistent differences among soybean cultivars for sensitivity to the disorder.

Publications

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.
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.

Biology and Ecology

Hobbs, H. A., Hill, C. B., Grau, C. R., Koval, N. C., Wang, Y., Pedersen, W. L., Domier, L. L., and Hartman, G. L. 2006. Green stem disorder of soybean. Plant Disease 90:513-518. [download] [view abstract]
Green stem is a disorder of soybean characterized by delayed senescence of stems with normal pod ripening and seed maturation. Two types of field experiments were conducted to test the relationship between green stem and Bean pod mottle virus (BPMV) and explore other potential factors that may be involved in the disorder. One experiment evaluated green stem and BPMV in collected leaf samples from individual plants in several commercial soybean fields during three growing seasons. Maturing plants (pods with full green seed) and leaf samples were tested by enzyme-linked immunosorbent assay (ELISA) for BPMV. The percentage of marked plants infected with BPMV in some fields was higher than the incidence of green stem at harvest maturity. Many plants infected with BPMV did not develop green stem, and conversely, many plants that had green stem were not infected with BPMV. An analysis of the numbers of plants in four possible classes indicated that green stem disorder was independent of BPMV infection (P = 0.98). Another experiment completed over two growing seasons in field cages showed that green stem developed without BPMV infection. BPMV infection did not increase green stem incidence in comparison to the caged controls. Insect feeding did not have an effect on level of green stem incidence. The exact cause or causes for the green stem disorder remain unknown.

Host-Pathogen Interaction

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.
Green stem trials conducted in seed cages Green stem trials conducted in seed cages
Normal stem and stem showing symtoms Normal stem and stem showing symtoms
Stick bug treatment in caged trial Stick bug treatment in caged trial