Effect of stem termination on soybean traits in southern US production systems

Southern U.S. soybean [Glycine max (L.) Merr.] are primarily determinate an d are grown in a diverse array of environments. Understanding the yield res ponse of different plant types to southern environments may lead to improve d yield. Our objective was to determine if varying stem termination could i ncrease yield in some environments. Eleven pairs of isolines varying for de terminate and indeterminate growth habit were derived from two crosses. All lines and controls were grown at two locations for 2 yr, planted in May an d June and with or without irrigation. Seven pairs were grown for a third y ear. Yield, height, lodging, and maturity data were collected. In all cross es and production systems, determinate lines were shorter, earlier maturing , and had less lodging than indeterminate lines. Yields of determinate and indeterminate lines were equal in all irrigation-planting date combinations , There was a trend for determinate lines to yield better than indeterminat e lines with early planting and irrigation. The yield difference between gr owth habits was conditioned primarily by a complex interaction of random ge netic and environment effects. The indeterminate growth habit may confer a yield advantage over the determinate growth habit in environments with limi ted yield and growth potential. This was due to the lower yield response to increasing environment productivity of indeterminate vs. determinate lines . Perhaps 10 to 15% of southern production environments have conditions whe re indeterminate types may yield better than determinate types. The yield a dvantage of indeterminate types in such environments appears small. The suc cess of deploying indeterminate cultivars to low-yield, low-growth southern environments to maximize yield will depend on accurately predicting where these environments will occur.