Effects of application of salicylic acid under the drought stress on morphophisiological and biochemical traits of two varieties of mung bean

One of the most common environmental stresses that affect plant growth and development is drought stress. This stress directly impacts plant morphology, physiology, and biochemistry of plants. Salicylic acid (SA) is a signaling molecule and hormone-like substance that plays an important role in growth and physiological processes, as well as in the regulation of plant growth and development. The purpose of this research was to determine the effects of SA foliar application on morphological, physiological, and biochemical traits of two mung bean genotypes under drought stress.

This experiment was conducted in 2020 at Shandel village, 13 Km away of Zabol. A split plot design within a randomized complete block design with three replications was used. The main-plots were included irrigation after 70 (as normal conditions), 120, and 180 mm evaporation (as stress conditions) from Class A Evaporation Pan, and the sub-plots include two local cultivars of Sistan and Parto mung bean, and sub-sub-plots included the foliar application of distilled water (control), foliar application of 0.5 and 1 mM SA. Drought stress was applied in the middle of the vegetative growth stage. The foliar application of SA was done in three stages: the vegetative growth stage (20 days after planting), beginning of flowering stage and end of flowering stage. After full plant maturity, plant height, biomass, grain yield and yield components, photosynthetic pigments (chlorophyll and carotenoid), Relative Water Content (RWC), and proline of mung bean were measured.

Analysis of variance of yield traits and yield components revealed significant differences between drought stress levels, cultivar, and application of SA for all traits. The interaction effects of drought stress in cultivar on plant height and grain yield at 1% probability level and on fresh and dry plant weight at 5% probability level were significant and non-significant, respectively, while the interaction effects on other traits were not significant. The interaction effect of stress and SA was significant for the number of pods per plant, thousand seed weight, fresh and dry weight of the plant, grain yield, and the number of pods per m2. The interaction effect between SA and cultivar were not significant on 1000-seed weight, fresh and dry weight of the plant. The interaction of stress × cultivars, and SA was significant on all traits except grain yield and the number of pods per square meter.Drought stress has a profound effect on photosynthesis and water potentials of plant. Grain Yield and yield components were better in Parto cultivar than local Sistan cultivar. It is possible that the presence of superior stress resistance genes in Parto cultivars has caused higher yield and yield components than the local cultivar. Application of SA increased pod production per plant. Foliar application of SA probably reduces flower loss by reducing the adverse effects of stress and increases the number of pods per plant and consequently the number of pods per square meter. Foliar application of SA increases photosynthesis by improving photosynthetic pigments. In addition, foliar application of SA enhances photosynthesis, resulting in an increase in 1000-seed weight. SA, as an important signaling molecule, promotes plant growth and induced abiotic stress tolerance. Likely SA increases growth and yield by increasing potassium, phosphorus, nitrogen, and calcium concentrations. The effect of this hormone on other plant hormones that increase vegetative growth and increase cell division in meristematic regions, and cell growth may also contribute to the growth enhancement.

Based on the present study findings, drought stress had a negative effect on all traits examined. The effect of SA at a concentration of 1 mM was the highest in non-stress conditions and in the Parto cultivar. The Parto cultivar was better compared to another cultivar. Foliar application of SA improved drought resistance in both cultivars. This improvement was greater in Parto cultivar than local Sistan cultivar. Based on the results of this experiment, it is recommended to improve the yield and growth characteristics of mung bean during stress conditions. It also seems that Parto cultivar performs better in Sistan's conditions than the local cultivar of Sistan.