The effects of pumpkin rootstock on photosynthesis, fruit mass, and sucrose content of different ploidy watermelon (Citrullus lanatus)

Pumpkin rootstock affects watermelon scion growth, fruit yield, and quality, but the mechanisms of related key enzymes and photosynthesis remain unclear. In this study, net photosynthetic rate (PN), chlorophyll (Chl) fluorescence parameters, fruit mass and sugar accumulation, and related key enzyme activities were determined during the fruit development stage in diploid and triploid watermelon lines and corresponding pumpkin rootstock-grafted lines. The results showed that pumpkin rootstock increased PN and Chl fluorescence parameters of diploid and triploid watermelon, indicating that pumpkin rootstock could increase photosynthesis, the utilization efficiency of light energy of diploid and triploid watermelon lines. Pumpkin-grafted lines had higher alkaline α-galactosidase activity and lower activities of insoluble acid invertase, sucrose phosphate synthase, and sucrose synthase than corresponding own-root lines in diploid and triploid watermelon. It indicates that pumpkin rootstock could increase the unloading of photoassimilates and reduce the conversion of photoassimilates into sucrose in diploid and triploid watermelon fruits.