This investigation was performed to evaluate 21 oat genotypes and varieties based on agronomic traits and drought tolerance indices under rainfed and irrigated conditions in Kermanshah, Iran during 2009-2010 cropping season. A randomized complete blocks design with three replications was used for each environment. Drought tolerance indices i.e., stress tolerance index (STI), stress susceptibility index (SSI), tolerance index (TOL), mean productivity (MP), harmonic mean(HAM) and geometric mean productivity (GMP) were calculated. The results of analysis of variance for cell membran stability, grain yield, biomass, straw yield, plant height, 1000 seed weight, number of panicles and number of grains per panicle in rainfed and supplemental irrigation conditions indicated that differences among genotypic were highly significant (p<0.01). The combined ANOVA indicated the significant differences among genotypes for all traits. A positive and significant correlation was observed between grain yield under rainfed(Ys) and irrigated (Yp) with MP, GMP , HAM, STI indicated that these indices are the most suitable indices to screen genotypes in drought stress condition. Brusher and Tarahumara had the highest MP,GMP,STI and HAM. Therefor, they could be know as the drought tolerant varieties. Principal component analysis introduced two components. First vector showed 78.68 percent of variations and the second PCA explained 20.98% of the total variability. It separates the stress–tolerant genotypes from non-stress tolerant ones. Cluster analysis classified the genotypes into three groups. 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 these materials. Therefore, breeders can select tolerant varieties of oat genotypes based on MP,GMP,STI and HAM.
