RECURRENT SELECTION FOR SEED SIZE IN SOYBEAN .3. INDIRECT EFFECTS ON SEED COMPOSITION

In soybean [Glycine max (L.) Merr.], correlations between seed yield a nd 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 res ulted in seed yield changes but usually not changes in seed size. The objective of this research was to examine the indirect effects of recu rrent selection for increased seed size on protein and oil concentrati on in a random mating population that segregates for male sterility. T he intermating population N79-1500 was divided into three subpopulatio ns designated SS1, SS2, and SS3. Male-sterile (MS) plants were selecte d for large seed size through four cycles in SSI and SS2 and three cyc les in SS3. Parental composites of each cycle were tested at four loca tions in North Carolina in 1987 and 1988. In MS seeds of SSI and SS2, the concentration of protein decreased linearly across cycles of selec tion. Oil concentration increased in MS seeds of SSI. There was no cha nge in protein or oil concentration in MS seeds of SS3. In male-fertil e (MF) seeds, protein decreased and oil increased in SS1 and SS2, whil e 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 co ncentration x seed yield) increased only in SS3 while total oil (oil c oncentration x seed yield) increased in SS2 and SS3. The identificatio n of a subpopulation (SS3), which did not decrease significantly in pr otein or oil percentage as seed yield increased and therefore increase d in total protein, suggests that selection as practiced in this study can be useful to improve these important traits.