Effect of application of plant growth regulators on growth and grain yield of bread wheat (Triticum aestivum L.) cultivars under terminal drought stress conditions

Plant growth regulators (PGRs) have been used to reduce losses of wheat grain yield under limited moisture conditions. The effect of three PGRs including cycocel, salicylic acid and brassinoestroeid on growth and grain yield of four bread wheat cultivars Chamran, Shiroudi, Pishtaz and Sirvan under normal and withholding irrigation after flowering was examined. The experiment was carried out as factorial split plot arrangement in randomized complete block design with three replications in 2014-15 and 2015-16 growing seasons. The results showed that water stress significantly reduced number of grains per spike, grain weight per spike, thousand grain weight, harvest index, biological yield and grain yield. However, water stress had the least effect on thousand grain weight (11.2%) and the highest effect (25.2 %) was observed on biological yield. Furthermore, application of PGRs, especially cycocel, increased spikes.m2, grains per spike, harvest index, thousand grain weight and grain yield. Cycocel, salicylic acid and brassinoestroeid, had positive non-significant effect on grain yield components. The highest grain yield was achieved from application of cycocel in both growing seasons (3696 and 4439 kg.ha-1, respectively). Also, the highest grain yield was obtainted from Sirvan cultivar in both growing season (3608 and 4448 kg.ha-1, respectively). According to these results, although water stress reduced yield and its components, the alleviating effect of PGRs could compensate some proportions of water stress effect. The compensatory effect of PGRs was 31.3, 23.5 and 23.2 percent for cycocel, salicylic acid and brassinoestroeid, respectively. Therefore, application of PGRs can be considered as an alternative way to alleviate the effect of terminal drought stress on grain yield of bread wheat cultivars.