M. Roostaei - Dryland Agricultural Research Institute, Agricultural Research, Education and Extension Organization, Maragheh, Iran.
R. Rajabi - Dryland Agricultural Research Institute, Agricultural Research, Education and Extension Organization, Sararood Campus, Kermanshah, Iran.
J. Jafarzadeh - Dryland Agricultural Research Institute, Agricultural Research, Education and Extension Organization, Maragheh, Iran.
R. Mohammadi - Dryland Agricultural Research Institute, Agricultural Research, Education and Extension Organization, Sararood Campus, Kermanshah, Iran.

Drought-tolerance and grain yield stability are among the most important aspects in adaptation and successful performance of rainfed winter bread wheat cultivars. The main objectives of this study were (i) to assess the effectiveness of drought tolerance indices for selection of drought-tolerant winter bread wheat genotypes, and (ii) to identify high-yielding genotypes with yield stability in variable environments. In this experiment, ۲۴ winter bread wheat genotypes were evaluated in ۱۲ yield trials under two moisture-regimes (rainfed and supplemental irrigation) in two dryland research stations differing in winter temperature (temperate and cold agro-climatic conditions) during three cropping cycles (۲۰۱۸-۲۰۲۱). Yield-based drought tolerance indices including; stress tolerance index (STI), geometric mean productivity (GMP), mean productivity (MP), tolerance index (TOL), stress susceptibility index (SSI) and yield stability index (YSI) were used to estimate drought tolerance levels of winter bread wheat genotypes across locations and cropping cycles. GGE-biplot technique was used for grain yield stability analysis. Combined-analysis of variance revealed that the main effects of cropping season, location, moisture-regime, genotype, and their interactions effects on grain yield were significant (P<۰.۰۱). The combined and yearly PCA-based biplots and correlation matrix analyses revealed that STI, GMP and MP were consistently correlated (P<۰.۰۱) with grain yield in either rainfed and irrigated environments, indicating the effectiveness of these indices for selection of high-yielding genotypes in both conditions. Based on these indices, G۱۳ (Chenab/GB-SARA-۲۷ IRW۲۰۰۹-۱۰-۰۲۳-۰MA-۰MA-۰MA-۰MA-۰MA-۶MA), G۱۴ (Chenab/GB-SARA-۲۷ IRW۲۰۰۹-۱۰-۰۲۳-۰MA-۰MA-۰MA-۰MA-۰MA-۷MA), G۱۱ (Dharwar Dry/Nesser//SARA-BW-F۶-۰۶-۸۵-۸۶-۲-۵ IRW۲۰۰۹-۱۰-۰۵۶-۰MA-۰MA-۰MA-۰MA-۰MA-۶MA) and G۲۲ (Unknown-۲) were the most drought-tolerant genotypes. GGE-biplot analysis identified G۱۱, G۱۳ and G۱۴ as high yielding genotypes with yield stability across environments. In conclusion, the genotypic variation for drought tolerance and grain yield stability found in this study should be further explored in the national rainfed winter bread wheat breeding programs in Iran.

winter bread wheat, Rainfed, drought tolerance indices, Grain yield, PCA and GGE biplot