SCREENING IRANIAN BREAD WHEAT LINES UNDER DIFFERENT WATER REGIMES USING YIELD BASED DROUGHT TOLERANCE INDICES

Drought stress is the most limiting factor affecting growth and productivity of crop plants including bread wheat. The objective of this study was to evaluate the power and ability of several drought tolerance indices to be used in screening 47 bread wheat lines under different water regimes. Stress tolerance index (STI), geometric mean productivity (GMP), mean productivity (MP), tolerance index (TOL), stress susceptibility index (SSI), yield stability index (YSI), yield index (YI), harmonic mean (HM), drought resistance index (DRI) and sensitivity drought index (SDI) were calculated from grain yield under drought stressed and irrigated conditions. Combined ANOVA on grain yield, thousand grain weight and test weight data revealed significant effects (P >= 0.01) for water regime, genotype and genotype x water regime interaction. Mean comparison of drought tolerance indices and grain yield validated the significant influences of drought stress on yield as well as significant differences among lines. Results of calculated Pearson's correlation coefficients and multivariate analyses showed that GMP, MP and STI indices were able to discriminate drought sensitive and tolerant genotypes. Cluster analysis using the drought tolerance indices divided the 16 genotypes into tolerant and susceptible groups. High broad-sense heritability was obtained for grain yield (45.1%), thousand grain weight (70.1%) and test weight (52.8%). There were positive and highly significant correlations between drought tolerance indices such as MP, GMP, STI and HM with yield in drought and irrigated conditions. Results of the principal components analysis (PCA) revealed that the first component (PC1) explained 61.0% of the total yield variation and exhibited a positive correlation with Ys, Yp, STI, GMP, MP, YI and HM. The PC2 explained 38.2% of the total yield variation and had a higher positive correlation with SSI, TOL and STI. Cluster analysis using the drought tolerance indices divided the 47 genotypes into tolerant and susceptible groups.