The effect of floral stimulus on flower sex expression in monoecious cucurbits was examined using a qualitative short-day plant, Sicyos angulatus L. Sicyos was induced to flower not only by grafting it onto a flower-induced plant of the same species but also by intergeneric grafting Onto the day-neutral plant Cucumis sativus L. or the quantitative short-day plant Luffa cylindrica Roem under noninductive long-day conditions. Sicyos plant grafted onto various cucumber varieties having different genetic backgrounds for their sex expression developed both staminate and pistillate inflorescences with similar sex expression. When the availability of floral stimulus was restricted as in the case of grafting of Sicyos onto young cucumber seedlings at the cotyledonary stage, most inflorescences appearing on the Sicyos were staminate ones. Pistillate flowers formed on the cucumber receptors substantially increased when they were grafted onto Sicyos donors which had a sufficient number of leaves induced by short-days as compared with those grafted onto noninduced ones. These results suggest that the availability of floral stimulus participates in the sex expression of flowers in Cucurbitaceae. Undeveloped pistillate inflorescences, which occasionally appear on Sicyos scion, flowered normally when N6-benzylaminopurine was directly applied to the inflorescence.
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Takahashi et al. (1982) studied this question.