Effect of foliar application of 5- aminolevulinic acid on growth, some physiological factors and yield of sweet pepper (Capsicum annuum L.) under drought stress

To study the effect of 5- aminolevulinic acid (ALA) on some physiological responses of Capsicum annuum under drought stress, a factorial experiment in randomized complete block design in four replications was carried out in greenhouse. This study was conducted with two main factors, 5-aminolevulinic acid in four concentrations (0, 0.25, 0.5, and 1 mM) and drought stress in three levels (irrigation at 100, 60 and 30% of field capacity). Exogenous application of 5- aminolevulinic acid protected pepper against drought stress that its protective effect was related to regulation of antioxidant enzymes. 5- aminolevulinic acid had significant effects on yield, total phenols, soluble sugars, polyphenol oxidase and superoxide dismutase activities, hydrogen peroxide concentration and leaf area, tolerance and harvest indices. In drought stress condition, total phenol content, soluble sugar contents, free radicals, hydrogen peroxide and activities of superoxide dismutase and polyphenol oxidase enzymes in leaves increased while growth parameters decreased. Thus it can be stated that the pepper plant treated with 5 - aminolevulinic acid the activity of antioxidant enzymes and compounds such as soluble sugar and total phenol improve and amend the effect of drought stress on the morphological and physiological characteristics.