Phylogenetic analyses and agronomical characteristics on parthenocarpy in different Cucurbitaceae genera using cross-pollination

Abstract

In a study of parthenocarpy induction after intergeneric pollination between plants belonging to nine cucurbit genera (Citrullus, Lagenaria, Benincasa, Cucumis, Diplocyclos, Coccinia, Luffa, Trichosanthes and Momordica), we found that parthenocarpy was induced after pollination with pollen from another genus. Parthenocarpy was induced in female flowers of watermelon only with pollen of bottle gourd; the two species are considered to be the most closely related among species in tribe Benincaseae, and bottle gourd pollens have specific factors that induce fruit set of watermelon. In other species, parthenocarpy was induced not only between closely related genera but also between distantly related genera. Parthenocarpy was not induced in female flowers of melon and bitter melon that received pollen from different species. From observations of pollen tube elongation in the pistil, we found that elongation was not necessarily related to parthenocarpy induction in some species. Most species produced fruit set only when pollinated, suggesting that pollen germination and pollen tube elongation generate a signal(s) to induce fruit enlargement. We consider that reception and transduction of the signal(s) depends on the origin of pistil and pollen and that the factors involved in the induction of parthenocarpy are present in both male and female organs. The phenomenon of parthenocarpy after pollination with pollen from a different genus seems to be conserved widely in Cucurbitaceae, but is not known in other plant families. The factors involved in this unique parthenocarpy in Cucurbitaceae are discussed.