Effect of Three Genes (Pd, Rpsa1, and ln) on Plant Height, Lodging, and Seed Yield in Indeterminate and Determinate Near‐Isogenic Lines of Soybeans1

Prior research indicated that the three genes, Pd (dense pubescence), Rpsal (Phytophthora resistance), and ln (narrow leaflet), tended to stimulate the vegetative growth of indeterminate soybean [Glycine max (L.) Merr.] near‐isogenic lines but failed to significantly increase seed yield or, in some environments, significantly decreased yields. It was postulated that this lack of a yield increase, or the occurrence of a yield decrease, may be due to the increased lodging often associated with the increased vegetative growth. These three genes were crossed into the indeterminate (lodging susceptible) and determinate (lodging resistant) near‐isogenic lines of the soybean cultivars, ‘Clark’ and ‘Harosoy’ and yield tested in the field at Urbana, IL in 1974 and 1975 to test this hypothesis. The addition of the Pd and Rpsal genes to the indeterminate near‐isogenic lines increased plant height and lodging but decreased yield. In the determinate near‐isogenic lines, where no lodging occurred, plant height was increased and yields were either increased or there was no difference in yield. The effect of the ln gene was similar to the Pd and Rpsal genes in the Clark cultivar, but differed in the Harosoy cultivar. Results of this research strongly support the hypothesis that failure of the vegetative growth stimulating genes, Pd and Rpsal, and to a lesser extent the ln gene, to increase seed yields, or in some cases significantly decrease yields, in the indeterminate near‐isogenic lines is duet to the increased lodging associated with the increased vegetative growth. These data indicate that in evaluating genes which stimulate vegetative growth, care should be taken to evaluate them in a genetic background where lodging does not become the yield limiting factor.