Abstract: To explore the germination capacity of watermelon seeds under high temperature stress and to investigate the effect of salicylic acid（SA）on the mitigation of heat stress during the germination period of watermelon seeds, in this study, watermelon seeds of ‘Beikang No. 1’ were selected as the test material and seven treatment groups were set up: CK1 for suitable temperature control 28 ℃（optimum temperature for seed germination）, CK2 for high temperature control 38 ℃, and 0.005, 0.010, 0.050, 0.100 and 0.500 mmol/L SA applied at high temperature. After soaking for 12 hours, the germination indicators of watermelon seeds were counted and relevant physiological indicators were measured. The results showed that low concentrations of SA （0.005-0.050 mmol/L）all improved germination potential, germination rate, germination index and vigour index of watermelon seeds, with 0.050 mmol/L SA having the best promotion effect, while higher concentrations inhibited seed germination. Compared with the high temperature control CK2, the activity of antioxidant enzymes POD and SOD were significantly increased by 35.10% and 34.79%, respectively, the MDA content was significantly decreased by 23.82% and the content of osmoregulatory substances soluble protein and proline were significantly increased by 22.54% and 34.83% in the SA treated group at 0.050 mmol/L. It can be seen that exogenous SA can further alleviate the inhibitory effect of high temperature stress on watermelon seed germination, improve the germination ability and heat resistance of watermelon seeds by altering the content of osmoregulatory substances, enhancing antioxidant enzyme activity and inhibiting membrane peroxidation. These results provide a theoretical basis for the production of watermelon under high temperature conditions.

Key words: watermelon, seed germination, high temperature stress, salicylic acid