Developing high-protein, high-yield soybean populations and lines

Developing high-yielding, high-protein soybean [Glycine max (L.) Merr.] lines is difficult because of the inverse relationship between seed yield and seed protein content. The objective of this study was to evaluate single cross and rapid back cross breeding methods to achieve both high seed yield and high protein content. 'AC Proteus' was used as the high-protein source and 'Maple Glen' was used as the adapted high-yielding parent. Six single plants were randomly selected from each of 149 F(3) progeny rows to develop 886 single cross derived lines. Reciprocal back cross populations were made using 60 F(1) plants from the single cross and the high-yielding parent, Maple Glen. Ten single plant selections were randomly taken from each of 80 F(1)-derived families to develop 800 back cross derived lines. In 1994, all lines were tested in the field. About 20% of lines were retained for testing through this breeding project from 1994 to 1996 although selection intensity differed across populations and years. In 1997, six single cross and nine back cross lines were tested at six locations in Eastern Canada. The seed yield and protein content of the single cross lines were not significantly different from the back cross derived lines. All the selected lines had higher seed protein content than did Maple Glen. Both breeding strategies produced lines with significantly higher seed protein content than Maple Glen. However, none of these lines had significantly higher seed yield than Maple Glen or a recently released high protein cultivar, AC Proteina. These populations exhibited a very low or no association between seed yield and protein (r = -0.06 to -0.21). Therefore, the parents may be useful sources of alleles which do not exhibit the usual pleiotrophic effect of low seed yield and high seed protein. The use of a back cross to the adapted parent following the single cross was not beneficial in the development of high yielding lines.