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The production of watermelon in soilless culture is increasing in importance as a complement of the grafting technique to control phytopathological problems. The influence of this crop production system in fruit quality, particularly in sugar accumulation patterns, have not been studied yet comparing different substrates and the production in soil. On the other hand, the use of the synthetic cytokinin CPPU as an alternative or complementary method to fruit setting in watermelon production is also increasing in importance and its influence on fruit quality are not well clarified. In the present experiment two setting procedures (CPPU sprayed to the pistilate flowers and hand pollination with male flowers of the diploid cultivar 'Dulce Maravilla') were compared in three growing media (perlite, coir dust and rockwool) in watermelon plants of the triploid cultivar 'Reina de Corazones' grafted onto 'Shintoza'. Plants were grown in a greenhouse from April to July. Yields, fruit weight, Hunter colour parameters and soluble sugars accumulation were determined by sampling fruits at 20, 25, 30, 35, 40 and 45 days after fruit setting. The substrate or fruit setting procedure did not influence yields. Fruit weight was significantly higher in plants grown in rockwool than in the other substrates and was not affected either by the fruit setting procedure. No interactions between both factors under study were found in any of the quality parameters analyzed. Sugar accumulation patterns and contents were similar to those found in other studies. CPPU delayed the internal redness colour and sugar accumulation, particularly of sucrose, but was dependent on substrates. The internal redness colour was faster in fruits grown in perlite. Little influence of the substrate was found in the fructose or glucose accumulation patterns but sucrose and total soluble solids were higher in fruits from plants cultivated in perlite. Since sugar accumulation in watermelon is affected by water availability, these results seem to be related to differences in the available water holding capacity of the substrates.

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