Green Stem Disorder of Soybean.

Green stem disorder of soybean (Glycine max) is characterized by delayed senescence of stems with normal pod ripening and seed maturation. Three different field research approaches were designed to determine the relationship of green stem disorder to Bean pod mottle virus (BPMV) and other potential factors that may be involved in causing this disorder. The first research approach surveyed green stem disorder and BPMV in individual plants monitored in several commercial soybean fields during three growing seasons. Leaf samples from maturing plants (growth stage R6) were tested by enzyme-linked immunosorbent assay (ELISA) for BPMV. The percentage of monitored plants infected with BPMV at growth stage R6 in some fields was higher than the incidence of green stem disorder at harvest maturity. Many plants infected with BPMV did not develop green stem disorder, and conversely, many plants that had green stem disorder were not infected with BPMV. According to a chi-square test of independence, the data indicated that green stem disorder was independent of BPMV infection at growth stage R6 (P = 0.98). A second research approach compared green stem disorder incidence in an identical set of soybean entries planted in two locations with different levels of natural virus infection. Despite differences in virus infection, including BPMV incidence, 20 of 24 entries had similar green stem disorder incidence at the two locations. A third research approach completed over two growing seasons in field cages showed that green stem disorder developed without BPMV infection. BPMV infection did not increase green stem disorder incidence in comparison to controls. Bean leaf beetle, leaf hopper, or stinkbug feeding did not have an effect on the incidence of green stem disorder. The cause of the green stem disorder remains unknown.