The variable nature of rainfall makes it difficult to select wheat genotypes for drought tolerance in most dry environments. This research was done to determine optimum drought tolerance indices from evaluations of 18 durum wheat (Triticum turgidum ssp. durum) genotypes to stress from drought and reduced water conditions. Genotypes selected for tests were planted in two experiments; one under dryland condition and another with supplemental irrigation (in anthesis and grain filling stages). The experiment was set up as a completely randomized block design with four replications at Gachsaran Agricultural Research Station in 2009-2010. On the basis of grain yield tested in conditions of dryland and supplemental irrigation five drought tolerance indices were assessed: mean productivity, geometric mean productivity, tolerance, stress susceptibility index and stress tolerance index. Drought stress significantly reduced the yield of some genotypes while others were tolerant to drought. These results provide information on genetic variability useful for breeding programs. Based on principal component analysis there was a high correlation between mean productivity, geometric mean productivity and stress tolerance index with grain yield in both conditions, these indices were identified as the more effective indices for durum wheat selection under drought and water limited environments. A bi-plot graph demonstrated that genotypes 18, G14, G4 and G11 were located within regions for potential yield and drought tolerance. Grouping in the cluster analysis confirmed the results of the bi-plot display. The same genotypes had the best ranking with low standard deviation among their ranks. So, they were recognized as tolerant genotypes that are high yielding in both dryland conditions and with supplemental irrigation. It was concluded that selection for yield under partial high water stress can identify superior cultivars, not only for dry environments, but also for those characterized by frequent mild and moderate water stress conditions; G18 is an example of such a genotype that was recently released for sowing in semitropical dryland regions in Iran.
