Response of Wheat Genotypes to Terminal Drought Stress Using Physiological Indices

In order to study the effect of terminal drought stress on yield and yield components and some physiological traits of wheat genotypes, a field experiment was conducted at the Research Farm of Agricultural College of Shiraz University during 2010-11 growing season in a split plot arrangement based on randomized complete block design with three replications. Main plots were assigned to irrigation treatment and the sub plots to sixteen wheat genotypes. Post anthesis cutting irrigation caused significant reduction in grain yield (GY), biological yield (BY), harvest index (HI), canopy temperature depression (CTD), grain number per spike, 1000 grain weight and relative water content (RWC). Under normal irrigation conditions, the highest grain yield was obtained from Zarrin cultivar, whereas, under drought stress conditions, the highest grain yield was obtained from Tabasi cultivar. The trait most sensitive to water stress was grain yield (mean reduction 51.6% compared to control) followed by harvest index (mean reduction 37.2% compared to control). Correlation coefficient results showed that under normal irrigation conditions the highest correlation was between grain yield and biological yield (0.844*) and under stress conditions was found between grain yield and grain number per spike (0.895**), CTD (0.771**) and 1000 Grain weight (0.689**). Evaluating of CTD trend under stress conditions showed that by passing time from applying cutting irrigation, canopy temperature (CT) gradually increases due to water unavailability. The most reduction in grain and biological yield under drought stress was observed in C-85-7 genotype, whereas, cv. Shiraz with the least reduction in these two components, was found a drought tolerant and yield stability cultivar. At both irrigation treatments, there was a positive correlation between grain yield and CTD; therefore, CTD may be a suitable index for selecting late-season water stress tolerant wheat cultivars.