Drought is one of the major factors limiting crop production in arid and semi-arid regions. Twenty wheat genotypes with wide range of sensitivity to drought, including 18 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 Agriculture in Shiraz University. Each experiment was conducted as a randomized completed block design with three

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... . The moisture level in one of the experiments was optimum (100% field capacity) while the second experiment was conducted under drought stress (45% field capacity). Several biochemical components including enzymatic (catalase, CAT; peroxidase, POD; superoxide dismutase, SOD and ascorbate peroxidase, APX) and non-enzymatic (proline and carotenoids, Car) antioxidant defense systems and some factors of oxidative damage (hydrogen peroxide, H 2 O 2 ; lipid peroxidation, LPO and membrane stability index, MSI) were analyzed in the two conditions. Drought stress caused significant increase in enzymatic antioxidant activities, proline content, H 2 O 2 and LPO content at the flowering stage, while Car content and MSI decreased significantly in all genotypes. Drought tolerant genotypes showed the highest enzymatic and non-enzymatic antioxidants, highest MSI and the lowest LPO and H 2 O 2 . This trend was reversed in susceptible genotypes. The enzymatic antioxidants had higher correlation than non-enzymatic with oxidative stress factors and yield stability index (YSI). POD showed the highest positive correlation with MSI and the highest negative correlation with LPO. H 2 O 2 and MSI showed the highest correlation with YSI. In present study, Kavir and Alamut varieties were selected respectively as the most tolerant and susceptible genotypes.