Evaluation of the effects of glycine betaine and gibberellic acid application on physiological characteristics, yield and yield components of cowpea under drought stress conditions conditions

Drought is one of the most important factors limiting growth and production in crops and therefore use of management methods to reduce the effects of drought is very important. Water deficit stress is one of the most important factors limiting the growth and survival of plants in arid and semi-arid regions of the world. Water is a major component of the fresh produce and significantly effects on weight and quality of plants. Also, water deficit may cause significant changes in the component yield and yield in plants. Iran with an average annual rainfall of 240 mm is included among arid and semi-arid regions of the world. Of the million hectares of cultivated region, only five millions are under irrigation because of intense water limitations. However, Iran is one of the world’s cowpea producers. Cowpea has been cultivated for many years in different parts of Iran. Therefore, high production and development of cowpea is important in coriander. This research was conducted to evaluate the effects of foliar application of glycine betaine (GB) and gibberellic acid (GA) on physiological characteristics, yield and yield components under drought stress conditions in cowpea.

To evaluate the effects of foliar application of glycine betaine (GB) and gibberellic acid (GA) on physiological characteristics, yield and yield components 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 relative water content, ion leakage, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, pod number per plant, seed number per pod, hundred seed weight, seed yield and biological yield.

The results of ANOVA indicated that the effects of irrigation regime, glycine betaine and gibberellic acid were significant for relative water content, ion leakage, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, pod number per plant, seed number per pod, hundred seed weight, seed yield and biological yield. The results of comparison of means showed that by increasing drought stress the traits of relative water content, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, pod number per plant, seed number per pod, hundred seed weight, seed yield and biological yield decreased but the ion leakage significantly increased. Nonetheless, exogenous application of glycine betaine and gibberellic acid increased relative water content, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, pod number per plant, seed number per pod, hundred seed weight, seed yield and biological yield but the ion leakage significantly decreased. It seems that glycine betaine and gibberellic acid improved the growth indices 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.

Generally, the results indicated that glycine betaine and gibberellic acid improved the growth indices 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