In order to evaluation of some physiological traits associated with improved drought tolerance in wheat, twenty Iranian wheat genotypes with wide range of sensitivity to drought, including eighteen varieties of bread wheat (Triticum aestivum L.) and two varieties of durum wheat (Triticum turgidum L.) were used in two separate field experiments in 2009-2010 at the Experimental Station of College of Agricultural in Shiraz University, Iran. Each experiment was conducted as a randomized completed block design with three replications. The experiments only differed with respect to their moisture levels (100% or 45% field capacity). The results showed that drought stress significantly (P < 0.05) increased relative water protection (RWP), stomatal resistance (Sr) and canopy temperature depression (CTD), and decreased relative water content (RWC) in the genotypes. Drought tolerant genotypes had higher RWC, RWP, Sr, CTD and cell membrane stability (CMS) as compared to intermediate and susceptible genotypes. Also durum wheat indicated similar behaviors of tolerant bread wheat under drought stress. There were positive and significant correlation between yield stability index (YSI) and physiological traits. YSI had the highest correlation with RWP under stress condition. In this study, RWP and RWC were selected as the best criteria for classification and screening of drought tolerant genotypes and also Azar2 and Alamut genotypes were identified as the most tolerant and susceptible genotypes ,respectively.
