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Kiwi Fruits

History 

Kiwifruit is native to north-central and eastern China. Cultivation of the fuzzy kiwifruit spread from China in the early 20th century to New Zealand, where the first commercial plantings occurred. 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. 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 “omelette”. 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.

Cultivars

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 can vary in size, shape, hairiness, and color. The flesh can vary in color, juiciness, texture, and taste. Some fruits are unpalatable while others taste considerably better than the majority of the commercial varieties.

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).

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’. 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 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.

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.

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.

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.

A commercially viable variety of this red-ringed kiwifruit, patented as the EnzaRed™, is a cultivar of the Chinese hong yang variety. 

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.  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. The Gold3 variety, marketed by Zespri as ‘SunGold’, is not quite as sweet as the previous Hort16A, with a hint of tanginess, 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. 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

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 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. This is also increased by using varieties specifically developed for pollination.

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.

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.

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 theethylene 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 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). 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.

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