Effects Of Different Stock Grafting On Fruit Quality And Physiological Mechanism Of Grafting Watermelon

At present, the cultivation grafting technique of watermelon has become an effective method in production. But the researches on the mechanism of the effect of grafting on the fruit quality of watermelon were rare. And the researches about watermelon grafting were focused on the selection of stock, grafting methods and so on. The research on the heat resistance of watermelon is very few, and the high temperature stress is the main factor of the cultivation of watermelon in summer. The effects of different rootstocks on growth, development and fruit quality formation of grafted watermelon in soilless medium culture have been studied in this paper. The mainly planted watermelon variety Zaojia and splice method has been used in the experiments. Three grafting treatments were selected as Zaojia/Jingxin-1, Zaojia/Yongzhen-8, Zaojia/0525 compared with the Zaojia(CK). The results were as follows:1. There was no significant effect on watermelon fruit weight, Vc content and lycopene content in three kinds of rootstocks. The content of soluble solids of Zaojia/0525 is the highest, 11.1%. The contents of glucose and fructose in three kinds of grafted watermelon fruit were lower than Zaojia. The content of sucrose in three kinds of grafted watermelon fruit was significantly higher than Zaojia. The content of sucrose in fresh of Zaojia/0525 was 3 times higher than Zaojia. There was little effect on the content of oxalic acid and tartaric acid of the grafted watermelon fruit in three kinds of rootstocks. Higher malic acid content was in Zaojia/Jingxin-1 and Zaojia/Yongzhen-8, 1.9mg/mL、2.08 mg/mL. The content of citric acid in fresh and pericarp of Zaojia/Yongzhen-8 were 1.9 times and 3.9 times respectively from Zaojia.2. The highest AI activity was flesh of Zaojia, 83.4 mg/g/h. The highest NI activity was Zaojia/Yongzhen-8, 161.8 mg/g/h. The activity of SPS of Zaojia/Jingxin-1 was 12.6 times higher than Zaojia. The accumulation of sucrose in the flesh of CK was regulated by NI, SS, SPS and AI. But the accumulation of sucrose in the fruit of grafted watermelon was regulated by NI and AI.3. High temperature stress inhibited the photosynthesis of watermelon seedlings, and decreased Pn and Tr. While before high temperature stress, the Pn and Tr of grafted seedlings were 2.35 and 1.67 times higher than CK. So grafting watermelon can alleviate the reduction of Pn and Tr. The Fv/Fm and qP of watermelon seedlings were decreased, and the qN was increased. Thus, the effects of high temperature stress on PSII damage in the leaves of watermelon seedlings can be alleviated by grafting.4. Under high temperature stress, the relative electrical conductivity in the leaves was increased and then decreased. In a certain extent, the effects of high temperature stress on membrane lipid peroxidation of watermelon can be reduced by grafting. The grafted seedlings could effectively enhanced the activities of CAT and APX in the leaves of watermelon before high temperature stress. Under high temperature stress, the activities of CAT and APX in the leaves of CK were significantly decreased. The activities of G-POD and SOD in the leaves of CK were significantly increased. The activity of G-POD in the leaves of CK reached the highest point at the fourth days. The activity of G-POD in leaves of grafted seedlings reached the highest point at the sixth days. So grafted seedlings than can maintain higher antioxidant activity than CK.