Drought Resistance and Dryland Adaption in Winter Wheat1

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Abstract
Nine winter wheat cultivars (Triticum aestivum L.) were evaluated for drought resistance and adaptation to a wide range of moisture‐limited environments (23 year‐location combinations). Drought resistance is described in terms of relative grain yield under severe soil moisture stress. Regression of the cultivar mean yield on the year‐location site mean yield was used to measure the environmental response of a particular cultivar. Low deviation mean square estimates indicated that cultivar response was highly predictable when based on site mean yield. The ideal cultivar, described as having both the high yield under the most severe moisture stress and a strong yield response (b ≥ 1.0) to more favorable environments, was not found. ‘Nugaines’ gave the largest b value, primarily due to its poor performance under severe stress; it could neither be considered drought resistant nor widely adapted. ‘Hyslop’ and McDermid' were the most widely adapted having better than average yields under the severe moisture stress and high yields under more favorable environments. The club wheats, ‘Paha’ and ‘Omar’, were not drought resistant; they yielded poorly under stress conditions. Paha responded well (large b) to better moisture conditions. ‘Yamhill’ and ‘Wanser’ were classified as drought resistant because of their high yields under severe stress. However, their small b values were not indicative of wide adaptation. The dissimilarity of morphological characteristics of ‘Yamhill’ and ‘Wanser’ suggest that different morpho‐physiological traits may condition their drought resistance. The degree of association of drought resistance and wide adaptation have implications in breeding to combine both traits in a single cultivar.