Enhancing drought tolerance in broccoli (Brassica oleracea L.) through melatonin application: Physiological and biochemical insights into growth, photosynthesis, and antioxidant defense mechanisms

Abstract

Broccoli is a well-known and high-value vegetable crop for its abundance of antioxidants and minerals. Despite its popularity, its production faces significant challenges from various abiotic stressors, particularly drought stress. Melatonin a multifunctional molecule within plants modulates environmental stresses including drought stress. Therefore, the current study aimed to evaluate the effect of melatonin application (0 and 100 μM) on broccoli under 100% field capacity (FC) (well-watered) and drought stress (50% field capacity). Foliar application of melatonin helped overcome drought-induced losses and enhanced plant height (23.72%), root length (43.47%), total chlorophyll contents (46%), carotenoids (60%) and yield (34.23%), glycine betaine (GB) (77.7%), whereas reducing the oxidative activities of hydrogen peroxide (H₂O₂) (20%) and leaf water potential (LWP) (33.35%) in broccoli plants. Antioxidant activities, i.e., superoxide dismutase (SOD), peroxide (POD), catalase (CAT), and ascorbate (APX) were further enhanced under melatonin treatment with 28.53%, 26.10%, 35.26%, and 33.33% respectively. Melatonin application significantly increased gas exchange characteristics by increasing stomatal conductance. Pearson correlation matrix and biplot were developed for the determination of trait association and treatment performance. Exogenous melatonin application decreased the oxidative damage brought on by the drought and increased the yield of broccoli.