Genotypic Variability in Symbiotic Nitrogen Fixation and Carbon Isotope Discrimination Among Peanut Genotypes Under Drought Stress.

Drought stress is one of the major environmental factors limiting peanut productivity. The vulnerability of peanut to drought varies depending on genotypic characteristics, crop growth stages and environmental conditions. The objective of this study was to evaluate the effects of drought stress on symbiotic nitrogen fixation and carbon isotope discrimination in various peanut genotypes. Two parental lines (Tifrunner and C76-16) and 14 recombinant inbred lines with varying drought tolerance characteristics were evaluated in rainout shelters under three irrigation regimes (irrigated control, middle-season and late-season drought) using a split-plot design with a randomized complete block design within. Symbiotic nitrogen fixation capacity and carbon isotope discrimination in different genotypes were evaluated by measuring ¹⁵N and ¹³C natural abundance for two years. Reduction in percentages of shoot N derived from the atmosphere (%Ndfa) was observed under two drought treatments in both years; a greater reduction was observed under middle-season drought than under late-season drought. In addition, middle-season drought negatively affected carbon isotope discrimination in both years although no difference in carbon isotope discrimination was observed under late-season drought. Variabilities in %Ndfa and carbon isotope discrimination were also observed among different genotypes. Under middle-season drought, both %Ndfa and carbon isotope discrimination were higher in drought tolerant lines than drought susceptible lines. Moreover, the most drought tolerant line identified in our previous yield study had the highest N-fixing capacity under both drought treatments in both years. Additionally, there was a positive correlation between %Ndfa and carbon isotope discrimination under both drought treatments.