Increasing Soybean Productivity through Selection for Nitrogen Fixation

Abstract

Abstract Nitrogen fixation and accumulation are major factors of soybean [ Glycine max (L.) Merr.] production. Investigations were carried out to determine whether higher N 2 fixation could be considered as a criterion for the improvement of productivity. A selection for N 2 fixation, which was based on acetylene reduction estimates, was carried out at Growth Stage R5. A set of 210 F 2 plants issued from three crosses and developed in nutrient solutions was studied in phytotronic chambers, under temperature and mineral N nutrition conditions that were favorable for the maximum expression of the symbiosis. The seed yield of the F 4 ‐derived lines was evaluated under normal population density on a Typic Udifluvent loamy‐sand soil (pH 6.0, organic matter 1.5%, and total N 1 g kg −1 ). Seed yield and N2 fixation were expressed with respect to the mean value of the genotypes with the same date of maturity. Seed yields of the F 4 ‐ derived lines were significantly correlated with the N 2 fixation of the F 2 parent plants. This correlation was observed for all of the plants investigated including all crosses ( r = 0.294 ** , significant at P = 0.01) and for each of the three crosses: Weber × Maple Arrow ( r = 0.433 ** ), Weber × Jiling 14 ( r = 0.394 * , significant at P = 0.05), Weber × Kingsoy ( r = 0.597 ** ). The seed yield of the F 4 lines was also significantly correlated with nodule volume and nodule dry weight, particularly at each cross level. High nodulation ability and high N 2 fixation rates appear to increase soybean seed yield. Early breeding for these traits may therefore be expected to result in a genetic gain in seed yield in the progeny.