Recurrent Selection for Seed Size in Soybean: III. Indirect Effects on Seed Composition

Abstract

In soybean [Glycine max (L.) Merr.], correlations between seed yield and seed composition are often significant, while correlations between seed size (a component of yield) and seed composition are usually low. In addition, selection for changes in seed composition have often resulted in seed yield changes but usually not changes in seed size. The objective of this research was to examine the indirect effects of recurrent selection for increased seed size on protein and oil concentration in a random mating population that segregates for male sterility. The intermating population N79‐1500 was divided into three subpopulations designated SS1, SS2, and SS3. Male‐slerile (MS) plants were selected for large seed size through four cycles in SS1 and SS2 and three cycles in SS3. Parental composites of each cycle were tested at four locations in North Carolina in 1987 and 1988. In MS seeds of SS1 and SS2, the concentration of protein decreased linearly across cycles of selection. Oil concentration increased in MS seeds of SS1. There was no change in protein or oil concentration in MS seeds of SS3. In male‐fertile (MF) seeds, protein decreased and oil increased in SS1 and SS2, while SS3 was unchanged for both constituents. On a weight per seed basis, there was a linear increase in protein and oil concentration of both MS and MF seeds of all three subpopulations. Total protein (protein concentration × seed yield) increased only SS3 while total oil (oil concentration × seed yield) increased in SS2 and SS3. The identification of a subpopulation (SS3), which did not decrease significantly in protein or oil percentage as seed yield increased and therefore increased in total protein, suggests that selection as practiced in this study can be useful to improve these important traits.