Kiwifruit

Kiwifruit by species
A = A. arguta, C = A. chinensis, D = A. deliciosa, E = A. eriantha, I = A. indochinensis, P = A. polygama, S = A. setosa.

A sliced kiwifruit

Kiwifruit (often shortened to kiwi) or Chinese gooseberry is the name given to the edible berries of several species of woody vines in the genus Actinidia.^[1][2] The most common cultivar group of kiwifruit ('Hayward')^[3] 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 and a sweet but unique flavor. It is a commercial crop in several countries, such as Italy, New Zealand, Chile, Greece, and France.^[4]

Etymology

Early varieties were described in a 1904 nurseryman's catalogue as having "...edible fruits the size of walnuts, and the flavour of ripe gooseberries..."^[5] and Europeans called it the Chinese gooseberry.^[1]

In 1962, New Zealand growers began calling it "kiwifruit" when exporting; the name becoming commercially adopted in 1974.^[1] The word kiwifruit and shortened "kiwi" has been used since around 1966 when the fruit was first imported from New Zealand to the United States.^[6][7]

Kiwifruit has since become a common name for all commercially grown fruit from the genus Actinidia.^[1][8]

In New Zealand, the shortened word "kiwi" is seldom used to refer to the fruit, as it usually refers to the kiwi bird or the Kiwi people.^[6][7]

History

Kiwifruit is native to north-central and eastern China.^[1] Cultivation of the fuzzy kiwifruit spread from China in the early 20th century to New Zealand, where the first commercial plantings occurred.^[1] Although kiwifruit is a national fruit of China, until recently, China was not a major producing country of kiwifruit, as it was traditionally collected from the wild.^[9] The fruit became popular with American servicemen stationed in New Zealand during World War II and later exported to California using the names "Chinese gooseberry" and "melonette".^[1][7] In 1962, New Zealand growers began calling it "kiwifruit" to give it more market appeal, and a California-based importer subsequently used that name when introducing the fruit to the American market.^[1]

Cultivars

Golden kiwifruit with a red-ring^[10][11]

The genus Actinidia contains around 60 species. Though most kiwifruit are easily recognized as kiwifruit (due to basic shape) their fruit is quite variable. The skin of the fruit varies in size, shape, hairiness, and color. The flesh varies in color, juiciness, texture, and taste. Some fruits are unpalatable while others taste considerably better than the majority of the commercial varieties.^[1][12]

The most common kiwifruit is the fuzzy kiwifruit, from the species A. deliciosa. Other species that are commonly eaten include golden kiwifruit (A. chinensis), Chinese egg gooseberry (A. coriacea), baby kiwifruit (A. arguta), Arctic kiwifruit (A. kolomikta), red kiwifruit (A. melanandra), silver vine (A. polygama), purple kiwifruit (A. purpurea).^[12]

Fuzzy kiwifruit

The larger fuzzy kiwifruit at rear compared to the smaller kiwi berry

Almost all kiwifruit sold belong to a few cultivars of fuzzy kiwi (Actinidia deliciosa): 'Hayward', 'Blake', and 'Saanichton 12'.^[2] 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.^[12] 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 flavor. '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 flavor is considered inferior.^[2][12]

Kiwi berries

Kiwi berries are edible berry- or grape-sized fruits similar to the fuzzy kiwifruit in taste and appearance, with thin, smooth skin. They are primarily produced by three species of kiwifruit; hardy kiwi (Actinidia arguta), Arctic beauty (A. kolomikta), and silver vine (A. polygama). 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.^[13]

The cultivar 'Issai' is a hybrid of hardy kiwi and silver vine which can self-pollinate. Grown commercially because of its relatively large fruit, Issai is less hardy than most hardy kiwi.^[14][15]

Golden kiwifruit

A sliced golden kiwifruit

The golden kiwifruit (Actinidia chinensis) has a smooth, bronze skin, with a beak shape at the stem attachment. Flesh color varies from bright green to a clear, intense yellow. This species is sweeter and more aromatic in flavor; the flavor is reminiscent of some subtropical fruit. Its short storage life currently limits its commercial potential. One of the most attractive varieties has a red 'iris' around the center of the fruit and yellow flesh outside. The yellow fruit fetches a higher market price and, being less hairy than the fuzzy kiwifruit, is more palatable for consumption without peeling.^[12]

A commercially viable^[16] variety of this red-ringed kiwifruit, patented as the EnzaRed™, is a cultivar of the Chinese hong yang variety.^[10][11]

Hort16A is a golden kiwifruit marketed worldwide in decreasing volumes because this variety suffered significant losses in New Zealand from late 2010 to 2013 due to the PSA bacterium.^[17] A new variety of golden kiwifruit, 'Gold3', has been found to be more disease-resistant and most growers have now grafted over to this variety.^[18] The Gold3 variety, marketed by Zespri as 'SunGold', is not quite as sweet as the previous Hort16A, with a hint of tanginess,^[19] and lacks the Hort16A's usually slightly pointy tip.

Cultivation

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.

Breeding

Kiwifruit growing on supported vine

Often in commercial farming, different breeds are used for rootstock, fruit bearing plants, and pollinators.^[1] 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.^[20] Therefore, most kiwifruits, with the exception of rootstock and new cultivars, are propagated asexually.^[20] 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.^[20]

Pollination

Kiwifruit flowering

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.^[1] Other varieties can self pollinate, but they produce a greater and more reliable yield when pollinated by male kiwifruit vines.^[1]

Kiwifruit is notoriously difficult to pollinate, because the flowers are not very attractive to bees. Some producers blow collected pollen over the female flowers. Generally, the most successful approach, 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.^[1] This is also increased by using varieties specifically developed for pollination.^[1]

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.^[1]

Storage

Fruits harvested when firm will not ripen when stored properly for long periods. This allows fruit to be sent to market up to 8 weeks after harvest.^[1]

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.^[21] 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.^[21] If stored appropriately, ripe kiwifruit normally keep for about one to two weeks.^[21]

Pests and diseases

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).^[22][23][24] In 2010 it was found in New Zealand's Bay of Plenty kiwifruit orchards in the North Island.^[25]

Scientists reported they had worked out the strain of PSA affecting kiwifruit from New Zealand, Italy, and Chile originated in China.^[26]

Production

Kiwifruit output in 2005

Top kiwifruit-producing countries in 2013
(in metric tons)

Rank	Country	Production (Tonnes)
1	China	1,765,847
2	Italy	447,560
3	New Zealand	382,337
4	Chile	255,758
5	Greece	162,800
6	France	55,999
7	Turkey	41,635
8	Iran	31,603
9	Japan	29,225
10	United States	27,300
	World	2,865,118
Source: UN Food & Agriculture Organization[27]

Kiwifruit exports rapidly increased from the late 1960s to early 1970s in New Zealand. By 1976, exports exceeded the amount consumed domestically.^[28] Outside of Australasia, all New Zealand kiwifruits are now marketed under the brand-name label Zespri.^[29]

China is now the largest producer of kiwifruit, growing almost four times as much as second-placed Italy in 2013. Other major producers include New Zealand, Chile and Greece.

In the 1980s, countries outside New Zealand began to export kiwifruit.^[30] In Italy, the infrastructure and techniques required to support grape production have been adapted to the kiwifruit. This, coupled with being very close to the European kiwifruit market, led to Italians becoming the leading producer of kiwifruit. 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 much of a factor.^[31]

Although kiwifruit is a national fruit of China, until recently, China was not a major producing country of kiwifruit, as it was traditionally collected from the wild.^[32] In China, it is grown mainly in the mountainous area upstream of the Yangtze River, as well as Sichuan.^[33]

Human consumption

A pavlova with strawberries, passionfruit, kiwifruit and cream

Kiwifruit may be eaten raw, made into juices, used in baked goods, prepared with meat or used as a garnish.^[1] The whole fruit including the skin is suitable for human consumption, but 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.^[1]

Raw kiwifruit contains actinidain which is commercially useful as a meat tenderizer. Actinidin also makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products which are not going to be served within hours, because the enzyme soon begins to digest milk proteins. This applies to gelatin-based desserts, as well, as the actinidin will dissolve the proteins in gelatin very quickly, either liquefying the dessert, or preventing it from solidifying.

Nutrition

A medium size kiwifruit (76 grams) provides 46 calories, 0.3 g fat, 1 g protein, 11 g carbohydrates, and 2.6 g dietary fiber found partly in the edible skin.^[34] Kiwifruit is a rich source of vitamin C (112% of the Daily Value per 100 grams) and vitamin K, and a good source of dietary fiber and vitamin E (nutrient tables, right).^[35][36]

Kiwifruit seed oil contains on average 62% alpha-linolenic acid, an omega-3 fatty acid.^[37] Kiwifruit pulp contains carotenoids, such as provitamin A beta-carotene,^[38] lutein and zeaxanthin.^[39]

Allergies

The actinidin found in kiwifruit can be an allergen for some individuals.^[40][41][42] The most common symptoms are unpleasant itching and soreness of the mouth, with the most common severe symptom being wheezing, with anaphylaxis also being reported.^[40][41]

The fruit is responsible for 10% of all allergic food reactions in children, making it a significant food allergen.^[43][44]

References

Further reading

• Vietmeyer, Noel D. (May 1987). "The Captivating Kiwifruit". National Geographic. Vol. 171 no. 5. pp. 683–688. ISSN 0027-9358. OCLC 643483454. 

External links

Wikimedia Commons has media related to Kiwifruit.

Wikispecies has information related to: Actinidia