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Pollination

Kiwifruit plants generally are dioecious, meaning a plant is either male or female. The male plants have flowers that produce pollen, the females receive the pollen to fertilise their ovules and grow fruit; most kiwifruit requires a male plant to pollinate the female plant. For a good yield of fruit, one male vine for every three to eight female vines is considered adequate. Some varieties can self pollinate, but even they produce a greater and more reliable yield when pollinated by male kiwifruit. Cross-species pollination is often (but not always) successful as long as bloom times are synchronised.

In nature, the species are pollinated by birds and native bumblebees, which visit the flowers for pollen, not nectar. The female flowers produce fake anthers with what appears to be pollen on the tips in order to attract the pollinators, although these fake anthers lack the DNA and food value of the male anthers.

Kiwifruit growers rely on honey bees, the principal ‘for-hire’ pollinator, but commercially grown kiwifruit is notoriously difficult to pollinate. The flowers are not very attractive to honey bees, in part because the flowers do not produce nectar and bees quickly learn to prefer flowers with nectar.

Honey bees are inefficient cross-pollinators for kiwifruit because they practice “floral fidelity”. Each honey bee visits only a single type of flower in any foray and maybe only a few branches of a single plant. The pollen needed from a different plant (such as a male for a female kiwifruit) might never reach it were it not for the cross-pollination that principally occurs in the crowded colony; it is in the colonies that bees laden with different pollen literally cross paths.

To deal with these pollination challenges, some producers blow collected pollen over the female flowers. Most common, though, is saturation pollination, in which the honey bee populations are made so large (by placing hives in the orchards at a concentration of about 8 hives per hectare) that bees are forced to use this flower because of intense competition for all flowers within flight distance.