Effects of Drought Stress on Symbiotic Nitrogen Fixation in Peanut

Drought stress is one of the major environmental factors affecting peanut productivity and its effect can be economically devastating when occurring at critical growth stages. The objective of this study was to evaluate the effects of drought stress on symbiotic nitrogen fixation in various peanut genotypes. Three drought treatments (irrigated control, middle-season and late-season drought) were applied to three separate rainout shelters. Two parental lines (Tifrunner and C76-16) and 14 recombinant lines (seven drought susceptible and seven drought tolerant genotypes) were planted in rainout shelters using a randomized complete block design within each drought treatment. The 15N natural abundance technique was used to evaluate differences in symbiotic nitrogen fixation[s}??]among different genotypes under drought stress. Both drought treatments negatively affected symbiotic nitrogen fixation; the middle-season drought treatment showed a greater reduction in the amount of N fixed compared with the late-season drought treatment. Proportions of shoot N derived from the atmosphere varied among different genotypes. Under middle-season drought, shoot N derived from N2 fixation for the drought tolerant lines was higher than those for the susceptible lines. The most drought tolerant line identified in our previous yield study had the highest N-fixing capacity under both drought treatments. There was no correlation between shoot N derived from N2 fixation and total shoot Nin the drought treatments although they were correlated in the irrigated treatment. Our results suggest that drought stress had a negative effect on symbiotic nitrogen fixation in peanut and the effect was more severe for mid-season drought.