Stress Tolerance and Adaptation in Spring Wheat1

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Abstract
Development of stress tolerant cultivars is an objective of many breeding programs, but success has been limited by inadequate screening techniques, and the lack of genotypes that show clear differences in response to well defined environmental stresses. Twenty spring wheat (Triticum aestivum L.) genotypes were evaluated over a range of water and high temperature‐stressed environments (15 location‐years) to establish standards for evaluation of stress tolerance screening techniques and to characterize genotypic stress tolerance and adaptation to stress environments. Overall and postanthesis stress tolerances were determined using grain yield and kernel weight responses, respectively. Stress tolerances were estimated using stress susceptibility indices (S), grain yields and kernel weights predicted for a hypothetical severe‐stress environment from regression parameters, and yields and kernel weights per se in five stress environments. Yield‐based stress tolerance estimates were correlated among all estimation methods. The stress susceptibility index identified stress tolerant genotypes that did not have outstanding yield performance per se in stress environments due to low yield potential, but which minimized yield loss under stress conditions. Kernel weightbased estimates of postanthesis stress tolerance using S were not correlated with predicted kernel weights in a hypothetical severestress environment or with kernel weights per se in five stress environments. Genotypes evaluated in this study exhibited a wide range in stress tolerance and adaptation to stress‐prone environments. Stress tolerant and susceptible genotypes were identified to use in evaluation of stress tolerance screening techniques. Used in tandem, regression analyses of genotype ✕ environment interactions, stress susceptibility indices, and stress performance per se, provided a more complete description of genotypic stress tolerances than did any analysis used alone.