Effects of grafting and cytokinin-induced fruit setting on colour and sugar-content traits in glasshouse-grown triploid watermelon

The effect on fruit quality of grafting and fruit set treatments, was determined in the triploid watermelon (Citrullus lanatus (Thun.) Matsum. and Nakai) cultivar 'Reina de Corazones' grown in a heated greenhouse. Grafting the scion onto 'Shintoza' (Cucurbita maxima X Cucurbita moschata) rootstock and setting fruit through application of the synthetic cytokinin CPPU [1-(2-chloro-4-pyridyl)-3-phenylurea] retarded the accumulation of sugar and development of the flesh colour of the fruit, compared to fruit from non-grafted, pollinated plants. The effects of grafting and of CPPU application on sugar accumulation were additive. At commercial maturity, the fruit of grafted and/or CPPU-treated plants had lower total soluble solids and sugar concentrations, and lower sucrose to hexose ratios, than fruit from control plants. Fruit from CPPU-treated plants also had a weaker red colour than fruit set by pollination. Despite this loss of quality, fruit from grafted plants, set with CPPU and grown in a heated greenhouse, had a total soluble solids concentration similar to fruit from pollinated, non-grafted plants, grown outdoors.