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Kiwifruit

ritau
06月04日
Kiwifruit (often shortened to kiwi outside Australia and New Zealand), or Chinese gooseberry, is the edible berry of several species of woody vines in the genus Actinidia. The most common cultivar group of kiwifruit (Actinidia deliciosa 'Hayward') is oval, about the size of a large hen's egg: 5–8 centimetres (2–3 inches) in length and 4.5–5.5 cm (1 3⁄4–2 1⁄4 in) in diameter. It has a thin, hair-like, fibrous, sour-but-edible light brown skin and light green or golden flesh with rows of tiny, black, edible seeds. The fruit has a soft texture with a sweet and unique flavour. In 2017, China produced 50% of the world total of kiwifruit.



Kiwifruit is native to central and eastern China. The first recorded description of the kiwifruit dates to the 12th century during the Song dynasty. In the early 20th century, cultivation of kiwifruit spread from China to New Zealand, where the first commercial plantings occurred. The fruit became popular with British and American servicemen stationed in New Zealand during World War II, and later became commonly exported, first to Great Britain and then to California in the 1960s.

Kiwifruit can be grown in most temperate climates with adequate summer heat. Where fuzzy kiwifruit is not hardy, other species can be grown as substitutes.



*Breeding
Often in commercial farming, different breeds are used for rootstock, fruit bearing plants and pollinators. Therefore, the seeds produced are crossbreeds of their parents. Even if the same breeds are used for pollinators and fruit bearing plants, there is no guarantee that the fruit will have the same quality as the parent. Additionally, seedlings take seven years before they flower, so determining whether the kiwi is fruit bearing or a pollinator is time-consuming. Therefore, most kiwifruits, with the exception of rootstock and new cultivars, are propagated asexually. This is done by grafting the fruit producing plant onto rootstock grown from seedlings or, if the plant is desired to be a true cultivar, rootstock grown from cuttings of a mature plant.

*Pollination
Kiwifruit flowering
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.

And for kiwifruit, honey bees are inefficient cross-pollinators 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 where 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, where 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.

Maturation and harvest
Kiwifruit is picked by hand and commercially grown on sturdy support structures, as it can produce several tonnes per hectare, more than the rather weak vines can support. These are generally equipped with a watering system for irrigation and frost protection in the spring.

Kiwifruit vines require vigorous pruning, similar to that of grapevines. Fruit is borne on one-year-old and older canes, but production declines as each cane ages. Canes should be pruned off and replaced after their third year. In the northern hemisphere the fruit ripens in November, while in the southern it ripens in May. Four year-old plants can produce up to 14,000 lbs per acre while eight year-old plants can produce 18,000 lbs per acre. The plants produce their maximum at 8 to 10 years old. The seasonal yields are variable, a heavy crop on a vine one season generally comes with a light crop the following season.

*Nutrition
In a 100-gram amount, green kiwifruit provides 61 calories, is 83% water and 15% carbohydrates, with negligible protein and fat. It is particularly rich (20% or more of the Daily Value, DV) in vitamin C (112% DV) and vitamin K (38% DV), has a moderate content of vitamin E (10% DV), with no other micronutrients in significant content. Gold kiwifruit has similar nutritional value, although only vitamin C has high content in a 100 gram amount (194% DV).

Kiwifruit seed oil contains on average 62% alpha-linolenic acid, an omega-3 fatty acid. Kiwifruit pulp contains carotenoids, such as provitamin A beta-carotene, lutein and zeaxanthin.
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