Drought Tolerance Topic 2016

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. We repeated last year's drought-stress experiment using the rainout shelter facilities at the USDA National Peanut Laboratory in Dawson, GA. Three treatments (irrigated control, middle-season and late-season drought) were applied to three separate rainout shelters. Two parental cultivars (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 among different genotypes under drought stress. The 13C natural abundance technique was used to determine carbon isotope discrimination, which has been shown to correlate with plant water use efficiency. Similar to last year, both middle- and late-season drought treatments negatively affected symbiotic nitrogen fixation; the middle-season drought treatment showed a greater reduction in the amount ofN fixed than the late-season drought treatment. However, the extent of negative impact was less severe in 2016. Proportions of shoot N derived from the atmosphere varied among different genotypes. Under the middle-season drought, shoot N derived from N2 fixation and carbon isotope discrimination were higher in the drought-tolerant genotypes than those in the susceptible ones. The most drought-tolerant genotype identified in our previous yield study had the highest N-fixing capacity under both drought treatments. There was a positive correlation between shoot N derived from N2 fixation and carbon isotope discrimination under both middle- and late-season drought treatments. Experiments conducted in Year 3 confirmed the findings of Year 2. Overall, these 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.