Evaluation of grain yield performance and tolerance to drought stress in wheat genotypes using drought tolerance indices

To evaluate drought tolerance in rainfed wheat genotypes، an experiment was conducted with 34 genotypes of bread wheat in two conditions (drought stress and non-stress) using randomized complete block design with three replications، in 2012-2013 growing season. Combined analysis of variance over two experiment showed that drought stress significantly decreased plant height، plant weight، peduncle weight and length، grain weight per spike، grain number per spike، 1000 grain weight، grain yield، chlorophyll content and day to ripening، but there was no significant effect on the harvest index and days to heading. Under the drought condition، the genotypes 7، 11 and 13 had the highest grain yield with an average of 4. 290، 4. 290 and 4. 260 ton. ha-1، respectively، while under the irrigated condition، the genotypes 13، 22 and 7 produced the highest grain yield with an average of 7. 44، 5. 96 and 5. 78 ton. ha-1، respectively. To identify drought tolerance genotypes، drought tolerance indices such as tolerance index (TOL)، stress susceptibility index (SSI)، mean productivity (MP)، geometric mean productivity (GMP)، harmonic mean (HMP)، stress tolerance index (STI) and yield stability index (YSI) were used. Results showed that GMP، MP، HMP and STI indices were positively correlated with grain yield under both stress and non-stress conditions. Therefore، they can be exploited not only to screen drought tolerance but also to identify superior genotypes for both stress and non-stress field conditions. Principal component analysis using grain yield under both conditions and drought tolerance indices showed that the genotypes 3، 7، 11 and 14 were the most tolerant genotypes to drought conditions، while the genotypes 4، 8، 30 and 32 were the most sensitive genotypes.