Applying exogenous plant growth regulators (PGRs) can be effective in plants coping with environmental stresses. So for more information, two field experiments were conducted to evaluate the effect of exogenous gibberellic acid (GA3), cytokinin (CK), and cycocel (CCC) on some physiological traits and defense mechanisms of two wheat cultivars (Sirvan and Homa) under four irrigation regimes: I0 (no-irrigation), I1 (irrigation at the booting), I2 (irrigation at the booting and anthesis), and I3 (irrigation at the booting, anthesis, and grain filling stages). These experiments were done in 2015–2016 and 2016–2017 seasons at the University of Kurdistan research farm as a split-split plot design with three replications. The results showed that drought stress increased malondialdehyde (MDA), electrolyte leakage (EL), superoxide dismutase (SOD) activity, proline, total phenolic (TPC), and total flavonoid content (TFC). Supplemental irrigation, especially I3, reduced amounts of these traits while increasing grain yield. CK application decreased MDA (20% and 16%) and enhanced proline (9.9% and 4%) and SOD (13.2% and 12.16%) in the first and second seasons, respectively, compared to control plants. Additionally, soluble protein content, TPC, TFC, and polyphenol oxidase (PPO) activity increased, while EL decreased with the application of all PGRs. In the first season, CK application significantly increased grain yield and in the second season, the highest grain yield (477.6 g m−2) was obtained in the Homa cultivar under the I3 irrigation regime combined with CCC application. Therefore, the application of CK and CCC could be recommended to enhance grain yield under these conditions.
