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  • Author or Editor: Julia Weiss x
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The reproductive biology of the climbing cacti Hylocereus polyrhizus (Weber) Britt. & Rose, H. undatus (Haworth) Britt. & Rose, H. costaricensis (Weber) Britt. & Rose, and Selenicereus megalanthus (Schum. ex Vaupel) Moran (syn. Mediocactus megalanthus) was studied with the aim of cultivating the cacti in Israel as fruit crops. Flowering in Hylocereus spp. occurred in two to three waves during the summer, whereas in S. megalanthus, flowering was concentrated at the end of autumn. Flowers of all species opened 1 to 1.5 hours before sunset and closed ≈6 hours after sunrise. In the Hylocereus spp., H. polyrhizus and H. costaricensis were self-unfruitful, and cross-pollination with other species led to high fruit set (100%). Hylocereus undatus was self-fruitful, setting fruit with self-pollen. Cross-pollination between the clones of S. megalanthus led to a high fruit set and each clone was self-fruitful. In contrast to H. undatus, S. megalanthus clones could set fruit without pollen vector involvement, although the set was slightly lower than with hand pollination. Pollen source influenced fruit weight. In the self-fruitful species of Hylocereus, fruit obtained by hand cross-pollination with other Hylocereus spp. were significantly heavier than fruit obtained by hand self-pollination. The largest fruit in each of the Hylocereus spp. were obtained by specific cross-combinations within the group. Fruit of S. megalanthus had a lower weight than fruit of the Hylocereus spp. Flowers of all species were visited by day-active honeybees only. Fruit set and fruit weight with open pollination was lower than with hand pollination in Hylocereus spp. Since stigma receptivity and pollen germinability stayed high during anthesis, the low pollination effectivity has to be related to other factors, such as the short bee visits and the absence of specific adaptation by the bees to the flower. In S. megalanthus, fruit set and fruit weight with open pollination were similar to values obtained with hand pollination. This similarity is probably related to the fact that pollen transfer in open pollination is achieved by bee visits and direct transfer of pollen to the stigma, which occurs via physical contact between anthers and stigma during flower closing.

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Hylocereus is a night-flowering cactus, whose hermaphrodite flowers reach a diameter of 22 cm. It was found in early studies that both self-fertility and self-sterility occur among the 14 species introduced to Israel. Flowers of all species behaved similarly concerning the phenology of flower opening and closing. Flowers opened about 1 hr. before sunset and were completely closed at approximately 6 hrs. after sunrise. Handcross-pollination led to 100% fruit set until 24 hrs. after flower opening, after which time both stigma receptivity and pollen germinability declined. Crossings between species bearing red fruits led to a higher fruit weight (424±134 g) in comparison to crossings between red-fruited species and species with yellow spiny fruits (146±64 g). Pollen germination in vitro for red-fruited species ranged from 23 to 59% but was only 0.7% for yellow-fruited species. To test the effectiveness of the honey bee as a pollinator a beehive was placed inside a nethouse. The flowers were visited by bees mainly in the morning; the bees foraged on pollen and eventually touched the stigmata of the flowers. Both the regularity of bee visits and the percentage of fruit set after bee visitation was very low (19%). This might be due to the fact that flowers were not constantly available; therefore the bees did not accept them as a constant and reliable pollen source.

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