Nitrogen fixation tolerance to soil water deficit among commercial cultivars and breeding lines of peanut

- Indian breeding lines in the field exhibited differences in nitrogen accumulation.
- Commercial lines did not show difference in nitrogen accumulation under field drought.
- Nitrogen fixation tolerance of commercial cultivars to soil drying was moderate.
- Field test was reasonable screen to identify genotypes for intensive measurement.

Peanut is often grown in the U.S. on sandy soil with limited water holding capacity. Since nitrogen fixation activity of other grain legume species, and some peanut cultivars, has been found to be especially sensitive to soil drying, yield improvement may be possible by identifying and/or breeding cultivars with nitrogen fixation resistance to water-deficit conditions. A key in this approach will be the use of screens to identify genotypes that may express drought resistance. Two screens of differing experimental sophistication were explored in this study as potential tools to compare genotypes. The first screen was done in the greenhouse using intact plants in a flow-though acetylene reduction system to measure nitrogen fixation response to soil drying over about two weeks. Ten commercial cultivars were tested and the only significant difference in nitrogen fixation activity was between Georgia 06G and York. The threshold for the decline in the nitrogen fixation rate averaged at a relative high value of 0.37 but Georgia 06G had a relatively low value of 0.28. These thresholds are greater than have been reported for nitrogen fixation tolerance in other species. The second, less sensitive screen that can be applied to a much larger number of genotypes was done in the field by measuring nitrogen accumulation over 2-3 wks of growth on limited available soil water. There were no differences in nitrogen-to-mass accumulation ratio among the commercial cultivars during two limited-water experiments. However, data collected from the field on several breeding lines from India indicated a consistency in the identification of nitrogen fixation in the greenhouse experiment and field experiments.