Water-Use Efficiency and Carbon Isotope Discrimination in Peanut under Water Deficit Conditions
- G. C. Wright,
- R. C. Nageswara Rao and
- G. D. Farquhar
Because of its relationship with water-use efficiency (W), carbon isotope discrimination in leaves (Δ) was proposed to be useful for identifying genotypes with greater water-use efficiency. In this study we examined the relationship between W and Δ in four peanut (Arachis hypogaea L.) genotypes. The genotypes were grown in and around mini-lysimeters embedded in soil and were subjected to two drought regimes, intermittent and prolonged water deficit conditions, by varying the irrigation timing and amount. Automated rain-out shelters prevented any rain from reaching the experimental plots during the treatment period. The mini-lysimeters allowed accurate measurement of water use and total dry matter (including roots) in a canopy environment. Water-use efficiency, which ranged from 1.81 to 3.15 g kg−1, was negatively correlated with Δ, which ranged from 19.1 to 21.8%. Tifton-8 had the highest W (3.15 g kg−1) and Chico the lowest (1.81 g kg−1, representing a variation in W of 74% among genotypes. Variation in W arose mainly from genotypic differences in total dry matter production rather than from differences in water use. It is concluded that δ is a useful trait for selecting genotypes of peanut with improved W under drought conditions in the field. A strong negative relationship existed between W and specific leaf area (SLA, cm3 g−1) and between Δ and SLA, indicating that genotypes with thicker leaves had greater W. SLA could therefore be used as a rapid and inexpensive selection index for high W in peanut where mass spectrometry facilities are not available.
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