BACKCROSSING HIGH SEED PROTEIN TO A SOYBEAN CULTIVAR

An inverse relationship between seed yield and seed protein concentration has limited success in developing soybean [Glycine mar (L.) Merr.] cultivars with high seed protein. High protein from the donor parent 'Pando' (498 g kg(-1) protein) was backcrossed to 'Cutler 71' (408 g kg(-1) protein) to determine if the yield of Cutler 71 could be recovered in addition to the high protein from Pando. Random F-4-derived lines, plus three Lines with highest seed protein concentration, from the initial cross, the BC1, and the BC2 populations, were evaluated for agronomic traits in separate, two-replicate tests for 1 yr at West Lafayette, IN. Seed from replication composites were evaluated for protein and oil concentration using near infra-red reflectance or near infra-red transmission. The parent line for each backcross was selected first for high seed protein, then for yield and agronomic similarity to Cutler 71. Random F-4-derived progenies of the BC3 population, the parent line for each backcross, and the cultivars Pando, Cutler 71, and Hamilton were evaluated in three-replicate tests for 2 yr at West Lafayette, IN. In each backcross generation, lines were identified with seed protein in excess of 470 g kg(-1) and that progressively approached the yield of Cutler 71. In the BC3 population, one Line averaged 472 g kg(-1) seed protein and was significantly (P = 0.05) higher in seed yield than Cutler 71, similar in yield to the cultivar Hamilton. In each backcross population, there were inverse relationships between seed yield and seed protein (R(2) values ranging from 0.33 to 0.06) and between seed protein and seed oil (R(2) values ranging from 0.55 in BC1 to 0.94 in BC3). In successive backcross populations, minimum oil values increased from 148 in BC1 to 174 g kg(-1) In BC3, indicating a trend toward recovering oil concentration (204 g kg(-1)) of Cutler 71. The data demonstrate that high seed protein can be backcrossed to a soybean cultivar, fully recovering the seed yield of the cultivar, suggesting the absence of physiological barriers to combining high seed protein with high seed yield in these populations.