Exogenous melatonin improves seed germination and seedling growth in greengram under drought stress

Drought stress diminishes seedling germination and vigor by reducing water uptake, inhibiting plant growth and development. Most of the pulse growing areas are under rainfed ecosystems, which significantly reduces crop yield. Melatonin, a growth-regulating compound, is widely used to mitigate the negative effects of abiotic stresses in pulses. With this background, a laboratory experiment was conducted to standardize the optimum melatonin concentration for seed treatment and foliar application in greengram, to minimize the ill effects of drought stress. The experiment was arranged in a completely randomized design (CRD) with three replications for each treatment. The treatments consisted of soaking seeds with different melatonin concentrations, viz., 20, 40, 60, 80 and 100 μM. Seeds were sown in a perti dishes and the drought stress was imposed using poly ethylene glycol 6000 (PEG 6000) @ - 0.4 MPa, and plates were maintained at room temperature (24-30 °C). After the seedlings emerged, various seedling growth parameters like germination percentage, shoot length, root length, vigor index, promptness index, germination stress tolerance index, fresh and dry weight of the seedlings, plant height stress index and root length stress index were recorded. The experimental results showed that drought stress significantly reduced germination percentage and other growth-related parameters in greengram seedlings compared to the melatonin treatments. Among the melatonin treatments, seeds treated with @ 100 μM concentration recorded the highest germination percentage (99.67 %), promptness index (98.80), vigour index (1631.68), shoot and root length (8.9 cm and 7.5 cm), fresh and dry weight of the seedlings (3.249 and 0.147 mg seedling-1) under PEG induced drought stress condition.