Effect of foliar application of brassinolide on grain yield and yield components of bread wheat (Triticum aestivum L.) cv. Sirvan under terminal drought stress conditions

To evaluate the effect foliar application of different concentrations of brassinolide on water productivity, grain yield and yield components of bread wheat (cv. Sirvan) under drought stress conditions, an experiment was carried out as spilt factorial arrangements using randomized complete block design with three replications at Zarghan filed station, Fars Province, Iran, dutring 2014-15 and 2015-16 growing seasons. Three levels of irrigation; optimum, withholding irrigation from flowering to grain filling stage and withholding irrigation during grain filling stage were assigned to main plots, and foliar application of brassinolide concentrations in three levels 0, 0.05 and 0.1 mg.l-1 and two timing of foliar application, before flowering and before grain filling, as factorial were randomized in sub-plots. Results showed that increasing foliar application of brassinolide concentration increased grain yield and water productivity under drough stress conditions. The lowest grain number per spike, thousand grain weight, grain yield, biological yield and harvest indexbelonged to drought stress from flowering to grainfilling stagewhich were reduced by 18.3, 13.1, 21.25, 11.33 and 11.78 percent, respectively, when compared to optimum irrigation conditions. The application of 0.1 mg.l-1 brassinolide increased grain number per spike by 9.17 percent, thousand grain weight by 6.62 percent and grain yield by 7.3 percent compared with contol. The highets water productivity (1.01kg.m-3) was observed in 0.1 mg.l-1 brassinolide application and also the longest duration to physiological maturity (193.5 day) was recorded in 0.1 mg.l-1 brassinolide application and optimum irrigation. The results of this study showed that drought stress from flowering to grainfilling stage had the most negative effect on bread wheat cv. Sirvan grain yield and foliar application of 0.1 mg.l-1 brassinolide improved this negative effect to some extent.