Exogenous melatonin enhances growth and physiological activities in cabbage (Brassica oleracea L.) under drought stress

Drought is a major abiotic stress which significantly impairs the growth and physiological activity of crops. Although melatonin is known to mitigate the abiotic stress-induced damage but its effects on cabbage under drought stress condition remains largely unexplored. As cabbage is a widely cultivated vegetable and drought stress is a significant concern in agriculture, the study investigates the effect of exogenous melatonin on the growth and physiological activity of cabbage under three different levels of drought following completely randomized design with seven treatments namely 90% field capacity-FC (control), 70%FC, 50%FC, 30%FC, 70%FC + Melatonin, 50%FC + Melatonin, 30%FC + Melatonin. A significant decline of 68.56% leaf area, 50.23% plant height, 37.65% SPAD (Soil Plant Analysis Development) value, 54.53% total chlorophyll contents of leaves and 50.73% photochemical efficiency of photosystem-II was recorded in 30% drought-stressed plant compared to control. However, melatonin treated plants showed better growth, pigment stability and photosynthetic efficiency compared to drought-stressed plants. Moreover, Melatonin application helped to retained cell structure and turgidity under drought stress. The antioxidant compounds and secondary metabolites accumulations increased under drought stress and were further increased were recorded by melatonin application which indicates enhanced defense mechanism in cabbage plants. Besides, the oxidative stress indicators declined significantly due to inducement of melatonin in drought stress condition and the highest reduction in oxidative damage (30.4% in hydrogen peroxide) and membrane damage (29.2% in malondialdehyde) were observed in melatonin treated cabbage plants under 50%FC compared to the corresponding untreated drought-stressed plants. These findings suggest that melatonin significantly alleviates drought-induced stress, promotes growth, physiological activities and antioxidant defense in plants.