HERITABILITY OF SEED SHAPE AND SEED SIZE IN SOYBEAN

Round seeds are desirable for food-type soybean [Glycine mar (L.) Merr .] cultivars and an understanding of the heritability of seed shape wo uld benefit the development of these cultivars. The objectives of this study were to estimate heritability of seed shape and seed size by pa rent-offspring regression, parent-offspring correlation, and realized heritability, and to determine the correlation between seed size and s eed 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 i n 1991 at Ottawa, ON, and their resulting F-2:3 progeny, grown in unre plicated rows in 1995 at Ottawa, were used for analysis. Seed shape wa s quantified by two aspect ratios (the ratio of minimum to maximum see d diameter), each calculated from a different seed orientation with di gital image analysis. Seed size (cross-sectional area) was measured in the same two orientations. Estimates of heritability for seed shape v aried across the four populations; parent-offspring regression coeffic ients ranged from 0.55 to 0.75, parent-offspring correlation coefficie nts ranged from 0.49 to 0.76, and realized heritability estimates rang ed from 0.59 to 0.79, Estimates of heritability for seed size ranged f rom 0.19 to 0.56 across populations. There mere significant positive c orrelations between the aspect ratios calculated from the two differen t orientations; therefore, selection for round shape in one orientatio n would result in indirect selection for round shape in the other orie ntation, There was no consistent association between seed shape and se ed size. In the natto population, < 5% of the F-3 Lines were smaller o r rounder than the smallest-roundest-seeded parent, Heritability estim ates indicate that plant breeders can select for round seed shape, on a single plant basis, in early generations of populations ranging in s eed size.