Abstract: In order to explore the physiological and biochemical changes of exogenous substances on the female flowers of Trichosanthes kirilowii under high temperature and strong light in summer, two-year-old Wanlou 9 was used as material, the effects of 200 μmol·L^-1 melatonin on the activities of antioxidant enzymes, osmotic regulators, H₂O₂, relative conductivity, pollen germination, fruit setting rate and single fruit weight of T. kirilowii under high temperature and strong light were studied. The results showed that the exogenous melatonin significantly increased activities of SOD, POD, CAT and APX, eliminated 34.5% of H₂O₂ compared with the control of T. kirilowii under high temperature and strong light. Moreover, it also promoted the synthesis and accumulation of osmotic regulators. Soluble sugar and proline in female flowers treated with exogenous melatonin increased by 25.8% and 45.5%, respectively, compared with the control. The exogenous melatonin also increased the pollen germination rate, promoted the fruit setting and fruit enlargement, and increased the fruit setting rate of T. kirilowii by 9.1 percent under high temperature and strong light. Above all, exogenous melatonin could significantly relieve the high temperature hazards and improve the fruit-setting rate by increasing the antioxidant enzyme activity and osmotic regulation ability under high temperature and strong light.

Key words: high temperature and strong light, Trichosanthes kirilowii, melatonin, physiological characteristics, fruit setting rate