Determining the best tolerance indices against drought stress in bread wheat genotypes in Gachsaran

In an attempt to identify drought tolerance lines and screen the quantitative parameters of drought tolerance, seventeen lines of bread wheat genotypes in addition to Koohdasht wheat were analyzed under two drought conditions, i.e. mild and severe stress, in a randomized complete block design with four replications in Gachsaran Dryland Agricultural Research Station. On the basis of the mild (Yp) and severe (Ys) stress yields, the quantitative parameters of drought tolerance including: mean productivity (MP), tolerance index (TOL), geometric mean productivity (GMP), harmonic mean (HM), stress susceptibility index (SSI), and stress tolerance index (STI) were measured. The results of the mean comparison indicated that there was a significant difference among all of the genotypes with respect to all of the indices and the yields in both environments. This demonstrated the existence of genetic diversity and the possibility of selecting the tolerant genotypes against drought and applying the superior ones in breeding programs. The results of the correlation analysis between the two conditions and drought tolerance indices indicated that the MP, GMP, STI, and HM indices were the best parameters for screening bread wheat genotypes. Considering these four indices and the high yield in the two conditions, the genotypes number 1 and 4 were selected as the most tolerant genotypes against drought. The biplot multivariate technique revealed that the genotypes number 1 and 4 were located along the vectors of drought tolerance indices. In addition, the spread of the genotypes in the biplot demonstrated the existence of genetic diversity among the genotypes regarding drought tolerance.