Effect of temperature and water deficit on water-use efficiency, carbon isotope discrimination, and specific leaf area in peanut

Carbon isotope discrimination (Δ) and specific leaf area (SLA) have been shown to be correlated with water-use efficiency (WUE) of peanut (Arachis hypogaea L.) and SLA has been proposed as an indirect selection criterion for Δ and WUE. The effect of high temperature and water deficit on WUE, Δ, and SLA, and relations between them, was investigated in controlled environments. Five Spanish (A. hypogaea ssp. fastigiata) and three Virginia (A. hypogaea ssp. hypogaea, botanical type) lines were grown at mean temperatures of 27 and 34°C and at 50 and 100% available soil water (ASW) from first flowering to maturity, and WUE, Δ and SLA measured at maturity. Virginia genotypes had higher total dry matter, water use and WUE (P ≤ 0.01), but were more sensitive to high temperature (P ≤ 0.01) than Spanish genotypes. Water deficit reduced water use and SLA, and increased WUE. The only water deficit x temperature interaction (P < 0.05) was for Δ, where water deficit reduced the value of Δ at 27°but not at 34°C. High temperature had no effect on water use, but decreased WUE and increased SLA. Across all water deficit and temperature treatments (n = 32), WUE was correlated with Δ (r = -0.78, P < 0.001) and SLA (r = -0.70, P < 0.001), and SLA correlated with Δ (r = 0.75, P < 0.001) with no difference associated with botanical type. Temperature and water deficit had significant (P ≤ 0.05) effects on the intercept, but not the slope of these relations. The results support the view that SLA can be used as an indirect selection criterion for Δ and WUE in genotypic selection.