WATER-USE EFFICIENCY AND CARBON-ISOTOPE DISCRIMINATION IN PEANUT UNDER WATER-DEFICIT CONDITIONS

Because of its relationship with water-use efficiency (W), carbon isot ope discrimination in leaves (Delta) was proposed to be useful for ide ntifying genotypes with greater water use efficiency. In this study we examined the relationship between W and Delta in four peanut (Arachis hypogaea L.) genotypes. The genotypes were grown in and around mini l ysimeters embedded in soil and were subjected to two drought regimes, intermittent and prolonged water deficit conditions, by varying the ir rigation 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 tot al dry matter (including roots) in a canopy environment. Water-use eff iciency, which ranged from 1.81 to 3.15 g kg(-1), was negatively corre lated with Delta, which ranged from 19.1 to 21.8%. Tifton-8 had the hi ghest W (3.15 g kg(-1)) and Chico the lowest (1.81 g kg(-1)), represen ting a variation in W of 74% among genotypes. Variation in W arose mai nly from genotypic differences in total dry matter production rather t han from differences in water use. It is concluded that Delta is a use ful trait for selecting genotypes of peanut with improved W under drou ght conditions in the field. A strong negative relationship existed be tween W and specific leaf area (SLA, cm(3) g(-1)) and between Delta an d SLA, indicating that genotypes with thicker leaves had greater W. SL A could therefore be used as a rapid and inexpensive selection index f or high W in peanut where mass spectrometry facilities are not availab le.