Applying a 200 ppm solution of CPPU to pollinated ovaries of watermelon (Citrullus lunatus Matsum) at anthesis increased fruit set from 26.9% (control) to 95%. Applying CPPU solutions to nonpollinated ovaries at anthesis induced parthenocarpy, yielding 65% and 89.5% fruit set, respectively with 20 and 200 ppm applications. However, 64% of the 20 ppm CPPU-treated parthenocarpic fruit stopped growth 10 days after treatment. Growth of CPPU-treated, pollinated, and nonpollinated fruit increased significantly compared with growth of control fruit during the first 10 days after treatment, but, except for the 20 ppm CPPU parthenocarpic fruit, growth subsequently slowed, resulting in fruit equal in size to the control by harvest. CPPU application did not affect soluble solids content of pollinated fruit, but reduced content of parthenocarpic fruit treated with 20 ppm. Fructose content was generally higher than glucose and sucrose at harvest. However, in pollinated fruit treated with 20 ppm CPPU, sucrose levels were higher than glucose and fructose. These results suggest that CPPU is practical for promoting fruit set and seedless fruit without adversely affecting fruit quality and development.

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Solutions of CPPU and BA were applied to ovaries of melon (Cucumis melo) flowers with or without pollination, and the effects on fruit set, growth, and sugar content were investigated. Treatment with CPPU increased fruit set in both seeded and seedless melons. Even at low concentrations, CPPU had a strong effect on fruit set in the seeded melons. In seedless melons, CPPU induced 100% parthenocarpic fruit set when applied with 10 mg·L–1; lower concentrations were much less effective. Treatment with BA increased fruit set in seeded melons, but was not particularly effective in the absence of pollination. During the first 10 days after anthesis, CPPU promoted fruit growth, but between 8 and 13 days after anthesis, the growth rate was lower than in the controls. Treatment with CPPU had little effect upon soluble solids (SS) levels in seeded fruit. SS content was significantly lower in seedless than in seeded fruit; this difference was larger in the placenta than in the mesocarp. Sucrose levels of both seeded and seedless fruits were consistently higher than glucose and fructose levels. High concentrations of CPPU reduced sucrose levels in the placenta of seedless fruit. These results indicate that seeds play an important role in sugar accumulation and melon fruit growth during later stages of development. Chemical names used: [1-(2-chloro-4-pyridyl)-3-phenylurea] (CPPU); 6-benzylaminopurine (BA).

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