Exogenous application of melatonin improves drought tolerance through ROS regulation in black gram (Vigna mungo L.)

Black gram yield has been reduced by 21–40% due to the severe drought-induced effects worldwide. Drought stress is a major limiting factor in black gram (Vigna mungo L.) production, particularly under rainfed conditions. This study was conducted to evaluate the effect of exogenous melatonin application on drought tolerance in the black gram variety VBN 11 under a controlled pot culture experiment during the flowering stage. The study employed a completely randomized design with ten treatments and four replications. Among the different melatonin concentrations, foliar application of 120 µM was identified as the most effective in mitigating drought-induced stress. Our study found that foliar spraying of melatonin significantly enhanced root morphological traits, including a 47.5% increase in lateral root number and a 24% increase in root diameter. It also improved physiological parameters such as chlorophyll content, SPAD value, relative water content, and water use efficiency. Biochemically, melatonin-treated plants exhibited higher levels of total soluble protein and nitrate reductase activity, along with increased proline accumulation and ROS scavenging enzymes (ascorbate peroxidase, catalase, and superoxide dismutase activity). On the other hand, melatonin reduced the accumulation of Reactive Oxygen Species, such as hydrogen peroxide and superoxide radicals, as well as lipid peroxidation, as indicated by malondialdehyde activity. These findings suggest that foliar application of 120 µM melatonin effectively enhances drought tolerance in black gram by improving root architecture, preserving photosynthetic efficiency, and activating antioxidant defense enzymes. In conclusion, melatonin holds promise as a sustainable approach for improving legume resilience under water-limited conditions.