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Increasing Soybean Productivity through Selection for Nitrogen Fixation

Laboratoire d'Amélioration des Plantes, Institut National Polytechnique (ENSAT), 145 avenue de Muret, 31076 Toulouse cédex, France

^* Corresponding author.

Nitrogen fixation and accumulation are major factors of soybean [Glycine max (L.) Merr.] production. Investigations were carried out to determine whether higher N₂ fixation could be considered as a criterion for the improvement of productivity. A selection for N₂ fixation, which was based on acetylene reduction estimates, was carried out at Growth Stage R5. A set of 210 F₂ 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 F₄-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 F₄- derived lines were significantly correlated with the N₂ fixation of the F₂ 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 x Maple Arrow (r = 0.433^**), Weber x Jiling 14 (r = 0.394^*, significant at P = 0.05), Weber x Kingsoy (r = 0.597^**). The seed yield of the F₄ lines was also significantly correlated with nodule volume and nodule dry weight, particularly at each cross level. High nodulation ability and high N₂ 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.

Received for publication February 19, 1990.