Biological nitrogen fixation in soybean with different levels of drought tolerance

Periods of drought may cause changes in the physiological condition of soybeans [Glycine max (L.) Merr.] and the biological nitrogen fixation (BNF) is one of the first processes to be impaired. The objective of this study was to evaluate the effect of water restriction in soybean genotypes on BNF related traits in order to select genotype(s) with drought tolerant BNF. The experiment was carried out under greenhouse, in a 5 x 2 factorial arrangement, with five genotypes (BRS 317, Jackson, R02-1325, R01-416F, and R01-581F) at two moisture levels, humid condition (80% of field capacity, FC) and drought condition (30% of FC). Drought induction started 33 days after sowing, at flowering, and was maintained for 10, 22, and 42 days. The evaluations were: number and mass of drought nodules; specific mass of nodules; ureide concentrations in leaflets, petioles, and nodules; total nitrogen in the leaves and the mass of grains per plant. Water restriction for 10 days reduced nodulation by 30%, grain mass by 35% for R02-1325 and R01-416F, and increased ureide concentration in nodules by 72% and in petioles by 90%. BRS 317, Jackson, and R01-581F stood out for exposure to drought for 10 days. At 22 days, BRS 317 stood out, while the other genotypes had reduction in grain mass by 36%, 40% in nodulation, and ureides in nodules by 34%. Exposure to drought for 42 days reduced nodulation by 46%, grain mass by 44%, leaf N by 15%, ureides in leaflets by 29 and 35% in petioles, with an increase of 136% of ureides in nodules. R02-1325 presented grain yield 30% higher than the other genotypes in wet condition and did not differ from the most productive ones under drought, indicating potential as source of drought tolerance in breeding programs.