Correlation Between Water-Use Efficiency and Carbon Isotope Discrimination in Diverse Peanut ( <i>Arachis</i> ) Germplasm

Stable carbon isotope discrimination (Δ) showed both intraspecific and interspecific variations in leaves collected from field plants representing a wide range of peanut germplasm grown in similar environments. It was predicted, on the basis of theoretical models relating Δ and water-use efficiency (W), that there could be as much as 60% variation in W. The Δ of leaf material was used as a guide to select peanut genotypes for testing, in the glasshouse, for a correlation between Δ and W. Pot plants of nine peanut genotypes were grown in conditions of unlimited water availability or very restricted water supply. Water-use efficiency and Δ of leaves was measured on all plants. A strong correlation (r = -0.81) was found between Δ and W. Water-use efficiency actually varied as much as twofold. Carbon content and Δ were measured in all parts of some plants. The Δ values of all parts were highly correlated with and therefore well-represented by the Δ of the leaves. Calculation of W on a molar basis removes variation associated with carbon content of dry matter. On this basis, W was correlated with the discrimination against 13C of the whole plant. The link between Δ and W is not direct but the strong correlation between Δ and W suggests that other factors, which are discussed, do not interfere greatly. The data provide more evidence that Δ might be used as a selection technique for W in C3 species.