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چکیده
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Drought is a wide-spread problem seriously influencing wheat (Triticum aestivum L.) production and quality, but development of resistant cultivars is hampered by the lack of effective selection criteria. The objective of this study was to evaluate the ability of several selection indices to identify drought resistant cultivars under a variety of environmental conditions. Eleven bread wheat cultivars differing in yield performance were grown in separate experiments under rain-fed (non-irrigated) and irrigated conditions at two locations in 2001–2003. Nonirrigated experiments experienced different levels of water stress due to variable rainfall over the years and locations. Nine selection indices including stress susceptibility index (SSI), stress tolerance index (STI), tolerance (TOL), regression coefficient of cultivar yield on environmental index (b), yield index (YI), yield stability index (YSI), mean productivity (MP), geometric mean productivity (GMP), and superiority measure (P) were calculated based on grain yield under drought-stressed and irrigated conditions. The results showed that under moderate stress, MP, GMP and STI were more effective in identifying high yielding cultivars in both drought-stressed and irrigated conditions (group A cultivars). Under severe stress, none of the indices used were able to identify group A cultivars, although regression coefficient (b) and SSI were found to be more useful in discriminating resistant cultivars. It is concluded that the effectiveness of selection indices in differentiating resistant cultivars varies with the stress severity. Wheat breeders should, therefore, take the stress severity of the environment into account in choosing an index.
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