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Large unisexual flowers and sticky pollen facilitate manual pollination in cucurbit breeding experiments. In squash, male and female flowers to be used the next morning are chosen the previous day. The closed corolla of an appropriate squash flower will have a light touch of yellow at the apex. The corolla tips of the staminate flower may be slightly separated also (Fig. 3.1). The apices of the chosen flowers are taped, tied or covered to prevent pollinator entry. The next morning, a staminate flower is removed and opened and the dehisced pollen is rubbed on to the stigma of a previously tied female flower. After pollination, the female flower is bagged, or the corolla re-secured to prevent pollinator contamination, and the developing fruit is then tagged.

Fig. 3.1. Cross-section of female and male flowers from Cucurbita pepo: (left) Spaghetti winter squash and (right) Patty Pan summer squash one day before anthesis, at which time the corollas are tied shut to exclude insects from flowers that are to be hand-pollinated.

Because squash pollen does not store well, the use of fresh pollen is customary in squash breeding. However, pollen can be used from pre-anthesis flowers that are kept for a few days at low temperature and high humidity (Robinson, 2010–2011). Also, pistillate flowers can be pollinated 1 day pre-anthesis. Cucumber can be pollinated 24 h after the flower opens, especially if pollinations are being made in the greenhouse or growth chamber and if the temperature is below 30°C.

Cross-pollination of andromonoecious melons and watermelons by hand is more difficult than for monoecious cultivars, since the anthers need to be manually excised from each perfect flower. The anthers of perfect flowers are usually removed on the afternoon before anthesis. Afterwards, the emasculated flower is enclosed to prevent insect pollination. As with squash, the male flowers of melon are either closed before anthesis or picked and kept indoors overnight at high humidity. Pollen transfer from these flowers takes place the following morning.