Heritability of Total and Fixed N Content of the Seed in Two Soybean Populations1

Abstract

Improved seed yield in the soybean [Glycine max (L.) Merr.] may result from selection to increase the N2‐fixing ability of the crop. To investigate that possibility, broad‐sense heritabilities of total and fixed N in the seed were estimated for two F2 soybean populations. One population was derived from a cross of high (‘Ware’) and low (D66‐5566) N2‐fixing parents and was grown years. The second population, grown in 1 year only, was derived from a cross of intermediate N2‐fixing parents (‘Williams’ and ‘Calland’). Both populations and their parents were grown in 15N‐labeled soil in the field along with ‘Clark’ rj1rj1 nonnodulating plants as controls. The amount of fixed N in the mature seed at harvest was determined by the 15N‐dilution method for individual plants. Broad‐sense heritability estimates of fixed N content of the seed ranged from 0.53 to 0.60. Estimates for percentage of fixed seed N varied from 0.12 to 0.43. Estimates for total seed N [as a weight (from 0.49 to 0.61) and as a percentage (from 0.20 to 0.87)], for seed yield (from 0.52 to 0.59), and for plant weights (from 0.57 to 0.62) are also reported. strong positive association was noted between seed dry weight and fixed N content of the seed (r = 0.99). These results suggest that improving N2 fixation in the soybean is feasible through selection based on the mass of fixed N in the seed. Selection for high seed yield will probably likewise result in the identification of plants with a high rate of N2 fixation.