Ameliorative effects of foliar spray of glycine betaine and gibberellic acid on cowpea (Vigna unguiculata L. Walp.) yield affected by drought stress

A 2-year field experiment was conducted in a research farm at Tehran, Iran, to determine the effect of mild and severe drought stress and foliar application of glycine betaine (0, 50, and 100 mM L−1) and gibberellic acid (0, 60, and 120 ppm) on some physiological traits and yield and yield-related traits of cowpea (Vigna unguiculata L. Walp.) genotypes. Drought stress at both mild and severe levels decreased relative water content (RWC), carotenoids, and total chlorophyll contents, while increased ion leakage which finally affected the yield of cowpea plants represented by 100-seed weight, number of pods per plant, and number of seeds per pod. Application of glycine betaine and gibberellic acid at all tested concentrations significantly alleviated the negative effect of drought on cowpea plants. The maximum relative water content, carotenoids, total chlorophyll, and yield were achieved by application of 120 ppm gibberellic acid and 100 mM glycine betaine at the three irrigation regimes. Gibberellic acid and glycine betaine succeeded in increasing cowpea plant tolerance to drought stress by improving vital plant components and preventing ion loss through ion leakage by controlling cell permeability. © 2021, Saudi Society for Geosciences.