Higher Intercellular CO₂ Concentration is Associated with Improved Water Use Efficiency and Drought Tolerance in Bread Wheat

In this study, the response of bread wheat genotypes to drought stress was evaluated on physiological and morphological basis. A group of 53 bread wheat genotypes, of diverse origin and morphology, was grown under well-watered and drought stress conditions. The tested genotypes were evaluated for carbon assimilation, water use efficiency, and morphological responses to drought stress. A highly significant variation was recorded among the tested genotypes on different physiological and morphological traits under drought stress. An increase in water use efficiency, intercellular CO₂ concentration, instantaneous water use efficiency and intrinsic water use efficiency was noted in the tested wheat genotypes under drought stress than that of well-watered control. However, the genotypes SQU-43, SQU-44, SQU-58, SQU-64, SQU-66, SQU-67, SQU-68, SQU-71, and SQU-74 had a higher net CO₂ assimilation rate than the rest of the genotypes under drought stress. Likewise, under drought stress, very little reduction in seedling dry weight of genotypes SQU-46, SQU-47, SQU-67, SQU-69, and SQU-72 was noted compared to the other genotypes. The tested bread wheat genotypes were clustered in three classes based on agglomerative hierarchical clustering. The variations within and between the classes were 70% and 30%, respectively. A significant variation was noted in the tested bread wheat genotypes under drought stress in terms of physiological and morphological responses. This variation can be useful for breeding programs aimed at developing drought tolerant bread wheat genotypes. The increase in intercellular CO₂ concentration was associated with improved water use efficiency and drought tolerance in bread wheat.