Drought tolerance enhancment in cotton (Gossypium hirsutum L.) by mepiquate chloride seed priming

To study pre-sowing seed treatment (seed priming) of hormone Mepiquat chloride (MC) (PIX) on physiological properties and increase drought tolerance in cotton (Shayan cultivar), a factorial experiment was performed in a completely randomized design with 3 replications. In this research, the seeds were initially exposed to two doses of the growth-regulatory hormone mepiquat chloride, including 5 and 10 g/l and control before being planted in pots.After the emergence of the plant from the soil, dry treatments based on the soil field capacity (FC) at three levels of irrigation at 25, 50, and 100% of field capacity for six weeks are applied to them, and growth indices, the activity of antioxidant enzymes, amount of hydrogen peroxide and malondialdehyde as well as changes in the two hormones of abscisic acid and endogenous gibberellin was investigated. According to the results of this research, the effect of seed priming with PIX and the interaction of drought × pre-sowing seed treatment on all physiological traits were significant at the level of 1%. The results of experimental data showed that drought stress (especially severe drought) reduced most growth indicator and physiological traits (fresh and dry weight of root and shoot, shoot length, fresh and dry weight of leaf, leaf area, root peroxidation activity, leaf phenol content, amount of gibberellin ) and only increased abscisic acid content (74%), root diameter (38%), root length(14%), leaf thickness, (15%) compared to the control. pre-sowing seed treatment with PIX, while increasing the dry weight (28% roots and 34% leaves) and thickness roots (58%) and 96% leaves (96%), increased catalase (88%) and peroxidase (6%) activity and abscisic acid content (73%) of leaves, reduced hydrogen peroxide (17%), malondialdehyde (20%) of leaves, and gibberellin (40%) of roots. Under extreme drought stress, the application of PIX decreased the amount of phenolic compounds in leaves by 44% as compared to the control. The interplay of drought stress × PIX decreased root gibberellin by 25% and raised leaf abscisic acid by 183%. According to the study results, seed priming with PIX improved the physiological and biochemical responses of cotton under drought conditions