Depodding Causes Green-Stem Syndrome in Soybean
- Dennis B. Egli * and
- William P. Brueninga
Green-stem syndrome in soybean (Glycine max L. Merrill) occurs when stems stay green after the pods mature causing problems during harvest. Green-stem syndrome has been linked to disease (primarily viruses), insects [principally stink bugs Nezara viridula (L.), Acrosternum hilare (Say), and Euschistus servus (Say)], and environmental stress, all of which could cause reductions in pod number. We evaluated the relationship between pod removal (25 and 50% of all pods) and the appearance of green-stem symptoms in a two-year field experiment at Lexington, KY (38°N). Depodding treatments were applied at the beginning of growth stage R6 to nine soybean varieties (three each from maturity groups III, IV, and V) grown in single-row plots with two replications. The progression of pod and stem maturation was determined at three-day intervals by visually estimating the proportion of the pods that had reached their mature color and by counting brown stems in a 10-plant sample. Pod removal had almost no effect on pod and seed maturation (delays for depodding were usually < 7 days) or on seed moisture when 95 to 100% of the pods were mature. Stem maturation was always delayed relative to control plants and the delay was larger for the 50% than the 25% treatment. Seventy percent of the variety by year combinations in the 50% treatment were delayed by > 20 days, but for 60% of the variety by year combinations the delay for the 25% treatment was ≤ 10 days. Stem maturation was not complete on some treatments when frost occurred 30 to 50 days after the controls matured. Soluble sugars, starch, and N accumulated in the stems of depodded plants and there was a significant (P = 0.01) linear relationship (r2 = 0.41) between soluble sugar enhancement (but not starch or N) and the delay in stem maturation. Depodding always created green-stem symptoms in all varieties, but the expression of the symptoms was not consistent across years. These results suggest that disease, insects, and environmental stress may cause green-stem syndrome indirectly by reducing pod load.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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