RELATIONSHIPS BETWEEN SEED YIELD AND SEED PROTEIN IN DETERMINATE AND INDETERMINATE SOYBEAN POPULATIONS

The development of soybean [Glycine mar (L.) Merr.] cultivars with hig h seed protein has been hampered by the inverse relationship between s eed yield and seed protein concentration. Determinate and indeterminat e near-isolines of soybean are usually similar in seed protein but dif fer in growth type. This study was conducted to determine if relations hips between seed yield and seed protein differed in populations of th ese two plant types. Determinate and indeterminate progenies were iden tified in two crosses between high-protein indeterminate breeding line s and determinate strains with average seed protein. The F-4-derived p rogenies were evaluated for 2 yr in three-replicate yield tests at Wes t Lafayette, IN. Seed protein and oil concentration were determined on seed from individual entries In each replication. Mean seed protein c oncentrations were similar for the two plant types in each cross. Regr ession of seed protein on seed yield was not significant among determi nate progenies in either cross. In contrast, negative slopes of regres sion lines were significant when seed protein was regressed on seed yi eld for indeterminate progenies in each cross. The three highest yield ing determinate entries from one cross were similar in yield to the de terminate cultivar Charleston and varied from 449 to 478 g kg(-1) seed protein compared with Charleston with 420 g kg(-1) protein. In the se cond cross, the three highest yielding determinate progenies were simi lar in yield to Charleston; two of these had higher seed protein than Charleston. The three highest yielding indeterminate lines in both cro sses were similar in yield to the indeterminate check cultivars Edison and Flyer and varied in seed protein from 418 to 435 g kg(-1) compare d with 414 g kg(-1) protein for Edison and 418 g kg(-1) for Flyer. The data demonstrate that in these two crosses, determinate progenies wer e a better source of selections that combined high seed yield with hig h seed protein than were indeterminate progenies.