Heritability of seed shape and seed size in soybean

Round seeds are desirable for food-type soybean [Glycine max (L.) Merr.] cultivars and an understanding of the heritability of seed shape would benefit the development of these cultivars. The objectives of this study were to estimate heritability of seed shape and seed size by parent-offspring regression parent-offspring correlation, and realized heritability, and to determine the correlation between seed size and seed shape in germplasm ranging in seed size. From parents differing in seed shape, four populations (three oilseed-type and one small-seeded natto-type) were generated. A total of 694 random F 2 plants, grown in 1994 at Ottawa, ON, and their resulting F 2:3 progeny, grown in unreplicated rows in 1995 at Ottawa, were used for analysis. Seed shape was quantified by two aspect ratios (the ratio of minimum to maximum seed diameter), each calculated from a different seed orientation with digital image analysis. Seed size (cross-sectional area) was measured in the same two orientations. Estimates of heritability for seed shape varied across the four populations; parent-offspring regression coefficients ranged from 0.55 to 0.75, parent-offspring correlation coefficients ranged from 0.49 to 0.76, and realized heritability estimates ranged from 0.59 to 0.79. Estimates of heritahility for seed size ranged from 0.19 to 0.56 across populations. There were significant positive correlations between the aspect ratios calculated from the two different orientations; therefore, selection for round shape in one orientation would result in indirect selection for round shape in the other orientation. There was no consistent association between seed shape and seed size. In the natto population, <5% of the F 3 lines were smaller or rounder than the smallest- roundest-seeded parent. Heritability estimates indicate that plant breeders can select for round seed shape, on a single plant basis in early generations of populations ranging in seed size.