Modification of Soybean Plant Architecture by Genes for Stem Growth Habit and Maturity1

Soybean Glycine max (L.) Merr. plant architecture can be modified by genes conditioning stem termination and timing of flowering and maturity. Nearisogenic lines of the soybean cultivars ‘Clark’ and ‘Harosoy,’ which possessed various genes for stem termination and maturity, were evaluated for agronomic performance and plant architectural features in furrow irrigation culture for 2 years. Genes delaying flowering and maturity significantly increased the number of main stem nodes, stem length, lodging, branches per plant, and seeds per plant, but reduced seed weight. Genes hastening flowering and maturity had the opposite effects. The gene for semldeterminate stem growth ( Dt 2 ) significantly reduced the number of main‐stem nodes and stem length, but the reduction in lodging was not significant. Differences in yield and other traits between semideterminate and indeterminate types were not significant. The gene for determinate stem growth ( dt 1 ) severely reduced the number of main‐stem nodes, substantially reducing stem length and lodging. There were significantly fewer 3‐seed pods in the dt 1 isolines, resulting in fewer seeds per plant. The lower seed yields of the dt 1 isolines were not significantly different, however, from their indeterminate counterparts. Delaying flowering in the determinate types lessened the severe stem length reduction caused by dt 1 , but lodging resistance was maintained. However, there was no advantage with respect to yield because delayed flowering resulted in a shorter reproductive period which tended to reduce seed weight. The number of pods borne on the main stem of nodes 15 cm or less from the soil surface was significantly greater in the determinate types than in indeterminate or semideterminate types, although delays in maturity tended to lessen this effect. As a consequence, harvest losses could be significant in determinate cultivars grown in furrow irrigation culture.