To evaluate the genetic diversity in 48 winter bread wheat genotypes originating from different countries, an experiment based on randomized complete block design with 4 replications was carried out in drip irrigation and rain-fed conditions at the field station of the Transitional Zone Agricultural Research Institute, Eskişehir, Turkey in 2011 and 2012. Based on grain yield under rain-fed and irrigated conditions, drought tolerance indices, i.e. stress susceptibility index (SSI), stress tolerance index (STI), tolerance index (TOL), mean productivity (MP), and geometric mean productivity (GMP), were calculated to identify genotypes with better yield and drought tolerance. Analysis of variance indicated that there were highly significant differences among the genotypes with regard to all the traits under the two experimental conditions. The correlation coefficients showed that STI, MP, and GMP were the most desirable selection criteria for high yielding and drought tolerant genotypes. Based on principle component analysis and biplot, genotypes numbered as 6, 11, 26, 41, 45, and 47 were susceptible genotypes. The genotypes numbered as 4, 12, 17, 24, 27, 28, 34, 35, 36, 38, and 42 were more stable under rain-fed conditions, while genotypes numbered as 9, 29, 31, and 44 were highly adapted to the irrigated conditions. Cluster analysis classified the genotypes into 3 groups: resistant, susceptible, and tolerant to drought conditions. In conclusion, this study showed that drought stress reduced the yield of some genotypes, while others were tolerant to drought, suggesting genetic variability of drought tolerance in this material. Therefore, breeders can select stress-resistant wheat genotypes based on the MP, GMP, and STI indices.
