Anti-stress effects of melatonin pre-treatment on germination indicators in tomato (Lycopersicon esculentum L.) under polyethylene glycol induced drought stress

Abstract: Tomato is a commercially grown vegetable crop that is susceptible to drought stress, which can be improved by understanding the tolerance mechanism. This study aims to evaluate the impact of melatonin pretreatment on alleviating PEG-induced drought stress on tomato. Initially, screening was performed with different polyethylene glycol (PEG) concentrations (-0.1, -0.2, -0.3, and -0.4 MPa), along with a control. The seeds treated with -0.3 MPa PEG exhibited lower germination percentage, seedling growth, and vigour index, while no germination was observed at -0.4 MPa. Therefore, -0.3 Mpa was selected as the sublethal osmotic concentration to assess the effect of melatonin to alleviate the osmotic stress. The seeds treated with various melatonin concentrations (20, 40, 60, 80, 100, and 120 µM) and untreated stress control were subjected to -0.3 MPa osmotic concentration, and absolute control was maintained. Seed germination parameters viz., germination indicators, shoot and root length indicators, biomass indicators, stress indices, and germination speed, were recorded. The results showed that the germination parameters were significantly reduced in stress control; however, notable improvements were observed in melatonin pre-treated seeds. Pretreatment with 100 µM melatonin led to an increase in germination percentage (61%), germination index (150.5), vigour index (1010.1), promptness index (65), shoot length (6.28 cm), root length (7.38 cm), fresh weight (0.66 mg), dry weight (0.07 mg), shoot length stress index (86), root length stress index (112), dry matter stress index (87), rate of germination (1.5% per day), germination rate index (15.1% per day), and coefficient of the velocity of germination (20.6) under drought stress. The study evidenced that melatonin pretreatment could effectively enhance seed germination under PEG-induced drought stress in tomato, which, therefore, can be recommended for further research.