Selection for large seed and high protein in two- and three-parent soybean populations

Soybean [Glycine max (L.) Merr.] cultivars with large seed size and high protein content are desirable for the production of tofu and other food products. The objectives of this study were to evaluate the amount of genetic variability and the effectiveness of single-plant selection for seed size and protein in two- and three-parent soybean populations. Two parents with large seed and high protein (LSHP) and one parent with normal seed size and protein (N) were used to produce three population types: LSHP X N, LSHP X LSHP, and LSHP X (LSHP X N). Four sets of the three population types were evaluated with different parents in each set. For each of the populations, 100 random F-2 plants and 10 plants of each parent were harvested at Ames, IA, and their seed size and protein were measured. The F-3 progeny of the 100 F-2 plants and 10 entries of the three parents of each set were evaluated in replicated tests at two Iowa locations. The percentage of F-2:3 lines with seed size greater than or equal to the smallest LSHP parent and protein greater than or equal to the lowest LSHP parent in the set averaged 4% for the LSHP X N, 88% for the LSHP X LSHP, and 31% for the three-parent crosses. Single-plant selection was not considered cost effective in the LSHP X N populations because the percentage of acceptable segregates was so small or in the LSHP X LSHP populations because the percentage of acceptable segregates was so high. For the three-parent populations, single-plant selection was most effective when the F-2 plants were ranked for the two traits and those with the most favorable rank were selected for evaluation as F-2:3 lines. LSHP X LSHP and three-parent populations should be the most useful for developing LSHP cultivars.