Evaluation of the effects of glycine betaine and gibberellic acid on antioxidant and biochemical traits of cowpea under drought stress conditions

Drought is a serious problem for production of crops such as bean which is sensitive to this stress. Therefore use of management methods to reduce the effects of drought is very important. To evaluate the effects of foliar application of glycine betaine (GB) and gibberellic acid (GA) on qualitative and quantitative characteristics under drought stress conditions, a factorial split plot experiment based on randomized complete block design with three replications was conducted during the 2018 crop year. Experimental factors included irrigation regimes (50, 70 and 90 mm evaporation from Class A evaporation pan) in main plots and glycine betaine (no foliar application, 50 and 100 mM) and gibberellic acid (no foliar application, 60 and 120 ppm) were in factorial form in sub plots. Data were collected on proline, malondialdehyde, catalase, superoxide dismutase, guiacol peroxidase, ascorbate peroxidase, glycine betaine, gebberellic acid, protein content and protein yield. The results of ANOVA indicated that the effects of irrigation regime, glycine betaine and gibberellic acid were significant for all the studied characteristics. The results of comparison of means showed that by increasing drought stress the gebberellic acid value, protein content and protein yield decreased but the proline, malondialdehyde, catalase, superoxide dismutase, guiacol peroxidase, ascorbate peroxidase and glycine betaine significantly increased. The exogenous application of glycine betaine and gebberellic acid at all levels of drought stress decreased malondialdehyde, catalase, superoxide dismutase, guiacol peroxidase, ascorbate peroxidase and increased the proline, glycine betaine, gebberellic acid, protein content and protein yield. Generally, the results of this study showed that the exogenous application of glycine betaine and gibberellic acid improved the growth of cowpea by reducing the adverse effects of drought stress. Therefore, exogenous application of glycine betaine and gibberellic acid can be used as a useful method for improving drought tolerance in cowpea. Also, the results showed that concentrations of 100 mM glycine betaine and 120 ppm gibberellic acid were more effective than other levels and induces more water stress tolerance in cowpea.