Kiwifruit (often abbreviated as kiwi), or Chinese gooseberry, is the edible berry of several species of woody vines in the genus Actinidia. The most common cultivar group of kiwifruit ('Hayward') is oval, about the size of a large hen's egg (5–8 cm (2.0–3.1 in) in length and 4.5–5.5 cm (1.8–2.2 in) in diameter). It has a fibrous, dull greenish-brown skin and bright green or golden flesh with rows of tiny, black, edible seeds. The fruit has a soft texture with a sweet and unique flavour. China produced 56% of the world total of kiwifruit in 2016.
The word kiwifruit and the shortened kiwi have been used since around 1966, when the fruit was first exported from New Zealand to the United States. Kiwifruit has since become a common name for all commercially grown green kiwifruit from the genus Actinidia. In New Zealand, the shortened word "kiwi" is never used to refer to the fruit, as it usually either refers to the kiwi bird or is a nickname for New Zealanders.
Early varieties were described in a 1904 nurseryman's catalogue as having "...edible fruits the size of walnuts, and the flavour of ripe gooseberries", leading to the name Chinese gooseberry. In 1962, New Zealand growers began calling it "kiwifruit" for export marketing, a name commercially adopted in 1974. A California-based importer, Frieda Caplan, subsequently used the name kiwifruit when introducing it to the American market.
"Kiwifruit" in Traditional (top) and Simplified (bottom) Chinese characters
|Literal meaning||"macaque peach"|
Kiwifruit is native to north-central and eastern China. The first recorded description of the kiwifruit dates to 12th century China during the Song dynasty. As it was usually collected from the wild and consumed for medicinal purposes, the plant was rarely cultivated or bred. Cultivation of kiwifruit spread from China in the early 20th century 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 was later exported, first to Great Britain and then to California in the 1960s.
In New Zealand during the 1940s and 1950s, the fruit became an agricultural commodity through the development of commercially viable cultivars, agricultural practices, shipping, storage, and marketing. Much of the breeding to refine the green kiwifruit and develop the gold Zespri was done by the Plant & Food Research Institute (formerly HortResearch) during the decades of 1970-1999. In 1990, the New Zealand Kiwifruit Marketing Board opened an office for Europe in Antwerp, Belgium, which became the headquarters for European marketing of Zespri gold kiwifruit in 2010. The general name, "Zespri", has been used for marketing of all green and gold cultivars of kiwifruit from New Zealand since 2012.
Species and cultivarsEdit
The genus Actinidia comprises around 60 species. Their fruits are quite variable, although most are easily recognised as kiwifruit because of their appearance and shape. The skin of the fruit varies in size, hairiness and colour. The flesh varies in colour, juiciness, texture and taste. Some fruits are unpalatable, while others taste considerably better than the majority of commercial cultivars.
The most commonly sold kiwifruit is derived from A. deliciosa (fuzzy kiwifruit). Other species that are commonly eaten include A. chinensis (golden kiwifruit), A. coriacea (Chinese egg gooseberry), A. arguta (hardy kiwifruit), A. kolomikta (Arctic kiwifruit), A. melanandra (purple kiwifruit), A. polygama (silver vine) and A. purpurea (hearty red kiwifruit).
Almost all kiwifruit sold belongs to a few cultivars of A. deliciosa (fuzzy kiwifruit): 'Hayward', 'Blake' and 'Saanichton 12'. They have a fuzzy, dull brown skin and bright green flesh. The familiar cultivar 'Hayward' was developed by Hayward Wright in Avondale, New Zealand, around 1924. It was initially grown in domestic gardens, but commercial planting began in the 1940s.
'Hayward' is the most commonly available cultivar in stores. It is a large, egg-shaped fruit with a sweet flavour. 'Saanichton 12', from British Columbia, is somewhat more rectangular than 'Hayward' and comparably sweet, but the inner core of the fruit can be tough. 'Blake' can self-pollinate, but it has a smaller, more oval fruit and the flavour is considered inferior.
Kiwi berries are edible berry- or grape-sized fruits similar to fuzzy kiwifruit in taste and appearance, but with thin, smooth green skin. They are primarily produced by three species: Actinidia arguta (hardy kiwi), A. kolomikta (Arctic kiwifruit) and A. polygama (silver vine). They are fast-growing, climbing vines, durable over their growing season. They are referred to as kiwi berry, baby kiwi, dessert kiwi, grape kiwi, or cocktail kiwi.
Actinidia chinensis (golden kiwifruit) has a smooth, bronze skin, with a beak shape at the stem attachment. Flesh colour varies from bright green to a clear, intense yellow. This species is sweeter and more aromatic in flavour compared to A. deliciosa, similar to some subtropical fruits. One of the most attractive varieties has a red 'iris' around the centre of the fruit and yellow flesh outside. The yellow fruit obtains a higher market price and, being less hairy than the fuzzy kiwifruit, is more palatable for consumption without peeling.
'Hort16A' is a golden kiwifruit cultivar marketed worldwide as Zespri Gold. This cultivar has suffered significant losses in New Zealand from late 2010 to 2013 due to the PSA bacterium. A new cultivar of golden kiwifruit, 'Gold3', has been found to be more disease-resistant and most growers have now changed to this cultivar. 'Gold3', marketed by Zespri as SunGold, is not quite as sweet as the previous 'Hort16A', with a hint of tanginess, and lacks the usually slightly pointed tip of 'Hort16A'.
Kiwifruit can be grown in most temperate climates with adequate summer heat. Where fuzzy kiwifruit (A. deliciosa) is not hardy, other species can be grown as substitutes.
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.
Kiwi plants generally have sexes, being either male or female. The male plants have flowers that produce pollen, the females receive the pollen to fertilise their ovaries.
In nature, the species is pollinated by birds and native bumblebees, which visit the flowers for pollen, not nectar. Therefore, in order to attract the pollinators to the female flowers, they produce fake anthers with what appears to be pollen on the tips, though it lacks the DNA and food value.
Most of the plants require a male plant to pollinate a female plant for the female plant to produce fruit (dioecious). For a good yield of fruit, one male vine for every three to eight female vines is required. Other varieties can self pollinate, but they produce a greater and more reliable yield when pollinated by male kiwifruit vines.
Kiwifruit is notoriously difficult to pollinate, because the flowers are not very attractive to the honeybees that farmers generically attempt to hire. This is, in part, because the flowers do not produce nectar. Honeybees are very inefficient pollinators in general, because they visit all species of flower indiscriminately, therefore the pollen needed for one plant is diluted. With Kiwi flowers it's worse, because the bees quickly learn to prefer other species of flowers actively, as the kiwi flowers don't have nectar.
To deal with this, some producers blow collected pollen over the female flowers. Most common, though, is saturation pollination, where the 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. This is also increased by using varieties specifically developed for pollination.
Maturation and harvestEdit
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.
Fruits harvested when firm will ripen when stored properly for long periods. This allows fruit to be sent to market up to 8 weeks after harvest.
Firm kiwifruit ripen after a few days to a week when stored at room temperature, but should not be kept in direct sunlight. Faster ripening occurs when placed in a paper bag with an apple, pear, or banana. Once a kiwifruit is ripe, however, it is preserved optimally when stored far from other fruits, as it is very sensitive to the ethylene gas they may emit, thereby tending to over-ripen even in the refrigerator. If stored appropriately, ripe kiwifruit normally keep for about one to two weeks.
Pests and diseasesEdit
Pseudomonas syringae actinidiae (PSA) was first identified in Japan in the 1980s. This bacterial strain has been controlled and managed successfully in orchards in Asia. In 1992, it was found in northern Italy. In 2007/2008, economic losses were observed, as a more virulent strain became more dominant (PSA V). In 2010 it was found in New Zealand's Bay of Plenty kiwifruit orchards in the North Island.
Scientists reported they had worked out the strain of PSA affecting kiwifruit from New Zealand, Italy and Chile originated in China.
In 2016, global production of kiwifruit was 4.3 million tonnes, led by China with 56% of the world total (table). Italy and New Zealand were other major producers. In China, kiwifruit is grown mainly in the mountainous area upstream of the Yangtze River, as well as Sichuan.
Kiwifruit exports rapidly increased from the late 1960s to early 1970s in New Zealand. By 1976, exports exceeded the amount consumed domestically. Outside of Australasia, New Zealand kiwifruit are marketed under the brand-name label, Zespri.
In the 1980s, countries outside New Zealand began to export kiwifruit. In Italy, the infrastructure and techniques required to support grape production were adapted to the kiwifruit. This, coupled with being close to the European kiwifruit market, led to Italians becoming the leading producer of kiwifruit in 1989. The growing season of Italian kiwifruit does not overlap much with the New Zealand or the Chilean growing seasons, therefore direct competition between New Zealand or Chile was not a significant factor.
|Nutritional value per 100 g (3.5 oz)|
|Energy||262 kJ (63 kcal)|
|Dietary fiber||1.4 g|
|Vitamin A equiv.|
|Pantothenic acid (B5)|
|†Percentages are roughly approximated using US recommendations for adults. |
Source: USDA Nutrient Database
|Nutritional value per 100 g (3.5 oz)|
|Energy||255 kJ (61 kcal)|
|Dietary fiber||3 g|
|Vitamin A equiv.|
|Pantothenic acid (B5)|
|†Percentages are roughly approximated using US recommendations for adults. |
Source: USDA Nutrient Database
Kiwifruit may be eaten raw, made into juices, used in baked goods, prepared with meat or used as a garnish. The whole fruit, including the skin, is suitable for human consumption; however, the skin is often discarded due to its texture. Sliced kiwifruit has long been used as a garnish atop whipped cream on pavlova, a meringue-based dessert. Traditionally in China, kiwifruit was not eaten for pleasure, but was given as medicine to children to help them grow and to women who have given birth to help them recover.
Raw kiwifruit contains actinidain (also spelled actinidin) which is commercially useful as a meat tenderizer and possibly as a digestive aid. Actinidain also makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products because the enzyme digests milk proteins. This applies to gelatin-based desserts, due to the fact that the actinidain will dissolve the proteins in gelatin, causing the dessert to either liquefy or prevent it from solidifying.
In a 100-gram amount, green kiwifruit provides 61 calories, is 83% water and 15% carbohydrates, with negligible protein and fat (table). 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, table).
The actinidain found in kiwifruit can be an allergen for some individuals, including children. The most common symptoms are unpleasant itching and soreness of the mouth, with wheezing as the most common severe symptom; anaphylaxis may occur.
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