Leaf Water Content and Gas‐Exchange Parameters of Two Wheat Genotypes Differing in Drought Resistance

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Abstract
It is still unclear what parameter(s), other than grain yield, might be a suitable indicator in a wheat (Triticum aestivum L.) breeding program for drought resistance. In this study, the leaf relative water content (RWC) and gas‐exchange parameters were compared between a drought‐resistant winter wheat genotype (cv. TAM W‐101) and a drought‐susceptible genotype (cv. Sturdy) to determine if these physiological parameters contribute to drought resistance in TAM W‐101. Plants were grown under well‐watered conditions in growth chambers until drought stress was imposed by limited watering of plants at anthesis or during vegetative growth. In both growth stages, TAM W‐101 maintained a higher RWC and apparent photosynthesis (A) than Sturdy under moderate to severe drought stress. TAM W‐101 plants also maintained a higher photosynthetic capacity (higher A at a given intercellular CO2 concentration [Ci]) under stress than did Sturdy in both growth stages. Photosynthetic water use efficiency (pWUE = A/stomatal conductance) generally increased with stress severity until very severe stress levels were attained. Thus, genotypic pWUE comparisons using stressed plants should be evaluated on a water‐status basis (e.g., RWC) to avoid the confounding effect of stress severity on pWUE. TAM W‐101 tended to have higher pWUE (RWC basis) than Sturdy under moderate to severe stress conditions, but not under well‐watered conditions. High leaf RWC, A, and photosynthetic capacity are traits that may contribute to drought resistance in TAM W‐101.