Abstract: The sugar metabolism and their related enzyme activities during fruit development of own-rooted and grafted on Hangzhou-long gourd , Chaofeng F₁, Yongshi and Figleaf gourd watermelon were studied. The results showed that the changes of sugar content and sucrose metabolism enzyme activity during the fruit development of different grafted and own-rooted watermelon were similar. At an early stage of fruit development, sugars accumulated slowly due to higher enzyme activity for sucrose cleavage than for sucrose synthesis. At a fruit ripening stage, the sugar content increased rapidly because the enzyme activity for sucrose synthesis was higher than for sucrose cleavage. However , the sugar content in the fruits of all grafted watermelons were lower than that in the fruit of own-rooted watermelon. Among the grafted watermelon fruits , the sugar content of the watermelon grafted on Chaofeng F₁ and Hangzhou-long gourd was higher than that of watermelon grafted on Figleaf gourd and Yongshi . The activities of invertase at the early stage, sucrose phosphate synthase and sucrose synthase at the late stage influenced by grafting may be responsible for the decrease of sugar content in the grafted watermelon fruit . The good relationship between sugar accumulation and net enzyme activity of sucrose metabolism indicated that sucrose metabolism enzymes including invertase, sucrose phosphate synthase and sucrose synthase may function together, which resulted in the difference of sugar content in own-rooted and grafted watermelon fruits.

Key words: Watermelon, Rootstock, Grafting, Sugar content, Sucrose metabolism enzyme activity