Abstract: With ‘Lanxin’ ‘Guixigua’ ‘Lingtong’ ‘Jinxing’ ‘Jingmei 8K’ ‘F57M’ as experimental materials, the treatments were set up: Nutrient solution + sprayed with water（CK）, nutrient solution containing 200 mmol/L NaCl+sprayed with water（T1）, nutrient solution containing 200 mmol/L NaCl+sprayed with 150 μmol/L melatonin（T2）. The growth indexes, chlorophyll, MDA contents and antioxidant enzyme activities of the nutrients were determined. The results showed that compared with CK, the plant height, stem diameter, biomass and chlorophyll content of watermelon seedlings under NaCl treatment were significantly reduced, and the growth was inhibited. Melatonin spray alleviated the growth inhibition induced by salt stress. After NaCl treatment, the MDA content in the leaves increased significantly. Compared with T1, the MDA content in the leaves decreased significantly after spraying with melatonin. Compared with CK, NaCl treatment significantly increased the activities of POD, CAT and APX in leaves, and the activities of SOD, POD, CAT and APX in leaves were significantly increased after melatonin spray. Exogenous 150 μmol/L melatonin spray can alleviate the damage caused by NaCl, improve the salt tolerance of watermelon seedlings of different varieties, and effectively promote the growth of watermelon seedlings.

Key words: salt stress, melatonin, watermelon seedlings, growth, antioxidant enzyme