Effects Of Grafting On Fruit Quality, Seedling Chilling Tolerance And Their Physiological Mechanisms In Watermelon (Citrullus Lanatus M.)

Grafting plays an important role in watermelon cultivation. Recent years, researches were mainly focused on selection of rootstocks, grafting methods and nutritional physiology of grafted watermelon plants, but the mechanisms of grafting on fruit qualities and seedling chilling tolerance of watermelon is still unclear. In this paper ,the physiological mechanisms of fruit qualities and seedling chilling tolerance in watermelon influenced by Grafting will be investigated by sugar metabolism of grafted watermelon fruit and physiological and biochemical changes of grafted watermelon seedling under chilling stress. The results of this study were as follows:1) The effects of four kinds of rootstocks on watermelon fruit quality were studied by comparing grafted plants with own-rooted ones. Hangzhou-long gourd (Lugenaria leucantha Rusby), Chaofeng F1 (Lagenaria siceraria Standl), Yongshi (Citrullus lanatus M.), Figleaf gourd(Cuarbita ficifolia) were used as rootstocks,Xiaolan(Citrullus lanatus M.var.citroides )was used as scion. The results showed that fruit shape, thickness of mescarp, Vc and protein contents were not affected by rootstocks, But total sugar content and soluble amino acid content, carotene content were decreased and flesh taste, flesh texture were deteriorated in fruits of four kinds of grafted watermelon compared to own-root watermelon. The yield of fruits grafted on Yongshi, Chaofeng F1 and Hangzhou long gourd was higher than on Figleaf gourd and own-rooted watermelon. Among grafted watermelon fruits, the quality of the fruits grafted on Chaofeng F1 and Hangzhou long gourd was higher than on Yongshi and Figleaf gourd. During fruit development, the sugar contents in the fruits of four kinds of grafted watermelon were lower than own-rooted watermelon, however, the decrease extent on Figleaf gourd and Yongshi was bigger.The contents of methyl acid and oxalic acid in the fruits of four kinds of grafted watermelon were similar to those of own-rooted watermelon during fruit development. But tartaric acid content and total acid content were higher and citric acid content was lower in the fruit of own-rooted watermelon than those of four kinds of grafted watermelon at the early stage and ripe stage of fruit development. SDS -PAGE showed that protein profiles in the fruit were influenced by grafting during the middle and late stages of fruit development.2) In both own-rooted and grafted watermelon fruit, sucrose is the main sugar in flesh tissue and hexose in mesocarp tissue. However, the sugar content of grafted watermelon fruit was lower than that of own-rooted watermelon fruit. The changes ofAbstractinvertase activities and sucrose synthase may be main reason responsible for the decrease of sugar content in the grafted watermelon fruit.3) The change trends of sugar contents and their related enzyme activities in the fruits of watermelon grafted on Hangzhou long gourd, Chaofeng Fi,Yongshi and Figleaf gourd were similar to those of own-rooted watermelon. At an early stage of fruit development, sugars accumulated slowly because the enzyme activities for sucrose cleavage were higher than for sucrose synthesis. At a fruit ripening stage, the sugars increased rapidly because the enzyme activities for sucrose synthesis were higher than for sucrose cleavage. However, the sugar contents in the fruits of all grafted watermelons were lower than those of own-rooted watermelon. Among the grafted watermelon fruits, the sugar contents of watermelon grafted on Chaofeng FI and Hangzhou-long gourd were higher than that of watermelon grafted on Figleaf gourd and Yongshi. The good relationship between sugar accumulation and sugar metabolism enzyme activities indicated that sugar metabolism enzymes including invertase, sucrose phosphate synthase and sucrose synthase behaved together, which led to the difference in sugar accumulation of own-rooted and grafted watermelon fruits.4) The assimilation capacity and sucrose content were higher in grafted watermelon leaves than those of own-root...