Evaluation of Recurrent Restricted Index Selection for Increasing Yield While Holding Seed Protein Constant in Soybean

Abstract

Yield and protein are important traits in soybean (Glycine max L. Merr.); however, genotypic correlations between seed yield and seed protein concentration are often negative, so that selection for one results in a decline of the other. Theoretically, restricted index selection allows maximum genetic gain in one or more traits while restricting genetic gain to zero in another set of one or more traits. The objectives of this study were to evaluate the use of a restricted selection index designed to increase yield while holding seed protein concentration constant; and to examine the efficiency of restricted index selection relative to direct selection for yield, protein concentration, and total protein. Two cycles of index selection resulted in a significant increase in yield and total protein, and no significant change in protein concentration. Cycle 2 parents yielded 171 kg/ha more than Cycle 0 parents and were 93 kg/ha greater in total protein. Linear regression of parental yield on cycle number showed the average increase per cycle for yield to be 86 ± 12 kg/ha. The average increase in total protein was 47 ± 4 kg/ha. These responses were similar to responses expected with use of the index. Selection based on the index was not expected to change oil concentration and no significant changes in oil were observed. In comparing the restricted index with the other selection criteria, direct selection for either yield or for total protein produced the greatest yield response. However, direct selection for yield or total protein is expected to result in significantly lower protein concentration in later cycles of selection. Thus, the use of restricted index selection appears to be the most promising long‐term approach to increasing yield while maintaining high protein concentration.