LAUSR

Abstract Drought stress affected the physiological traits of wheat. Furthermore, brassinolide (BR) hormone is imperative regarding distressing on some plant physiological characteristics under the drought stress. This experiment was conducted to investigate the effect of drought stress as well as concentration and time of application of brassinolide as a split-plot factorial based on randomized complete block design with three replications over 2014–2015 and 2015–2016. Irrigation regimes were carried out as the main plot including full irrigation, irrigation interruption from the beginning of flowering to grain filling and irrigation break from the commencement of grain filling to the physiological maturity, and factorial concentrations of brassinolide (0, 0.05 and 0.1 mg/l) and spraying time (before flowering stage and seed filling stage) were implemented as a subplot. The highest soluble carbohydrate, malondialdehyde (MDA), proline, and leaf electrolyte leakage (EC) (in the flowering stage) and the lowest chlorophyll, carotenoids, Fv/Fm, and relative water content (RWC) of leaves (in the grain filling) belonged to the conditions of irrigation interruption at the flowering stage. But these values have significantly improved with the application of 0.1 mg/l brassinolide before flowering. Moreover, the grain yield was increased in both irrigation interruptions at flowering and grain filling after spraying 0.1 mg/l brassinolide by 18 and 20%, respectively. In general, the irrigation interruption at the wheat flowering stage had the most detrimental effect on the physiological characteristics of wheat and the use of 0.1 mg/l brassinolide compared to control and 0.05 mg/l brassinolide, could recover the drawback effects.