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Kiwifruit – Actinidia deliciosa (A. Chev.)



KIWIFRUIT TAXONOMY

*Kiwifruit – Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson

Kiwifruit belongs to the Actinidiaceae family, containing four genera and about 285 species – mostly subtropical woody vines. The cultivated kiwifruit was referred to as Actinidia chinensis var. hispida until the mid 1980′s, when taxonomists split A. chinensis Planch. into two separate species, based largely on fruit size and hairiness. The smaller fruited, smooth-skinned variant maintained the name A. chinensis, whereas the cultivated kiwifruit with larger, hairy fruit is now given separate species status – A. deliciosa (A. Chev) C.F. Liang et A.R. Ferguson.

Related species include A. chinensis, A. arguta and A. kolomikta. A. chinensis is collected from the wild in China, and is preferred over A. deliciosa by the Chinese due to its hairless, better-flavored fruit. ‘Issai’ hardy kiwi (A. arguta) is offered by mail order nurseries for dooryard planting. It is hermaphroditic, bearing and flowers on the same plant (polygamodioecious?). Rumour has it that the Japanese are paying big bucks for these small, hairless kiwis, and a cottage industry is emerging. A. kolomikta is often growth as an ornamental vine, for its pink and white variegation of younger leaves. Other ornamental types include A. eriantha whith white pubescence on fruit and current growth and pink flowers, and A. polygama with fragrant flowers. The name “kiwi” or “kiwifruit” replaced “Chinese gooseberry” in the 1960′s, coined by the first Americans to import the fruit from New Zealand. Of course, the real kiwi is the round, brown, flightless bird from NZ, which this fruit resembles. The French also have a humorous name – “souris vegetale” meaning “vegetable mouse”.

Cultivars: Kiwifruit is dioecious, having separate male and female plants.

Female: ‘Hayward’ dominates the world industry, due to large fruit size, excellent flavor and storage qualities. ‘Abbott’, ‘Bruno’, and ‘Monty’ are other females grown to a very limited extent (< 1% of production). ‘Chico Hayward’ or ‘Chico’ was a large-fruited selection of ‘Hayward’ sent from New Zealand to Chico, California by Hayward Wright; it is virtually indistinguishable from ‘Hayward’.

Male (pollenizers): ‘Matua’ and ‘Tomouri’.

ORIGIN OF ACTINIDIA DELICIOSA (A. CHEV.), HISTORY OF CULTIVATION

Actinidia species are native to mountainous south and central China; the descendants of cultivated kiwifruit are native to southwestern China, where temperatures are warm and winters mild. They are found climbing into forest canopies, often draping entire trees like kudzu. Also, they can creep along the ground and form stout shrubs in more open, dry, exposed sites. The Chinese collected the fruit from the wild for thousands of years, but never domesticated the plant. Botanists who visited China around the turn of the century introduced seeds into Europe, the US, and New Zealand. However, commercial cultivation began first in New Zealand around 1930. The success of the New Zealand industry, especially since 1960, sparked interest in France, Italy, California, Chile, and Japan, where it is now grown commercially. Plantings also exist in Greece and Australia, among other countries. The California industry developed during the 1970′s, and is stabilizing at 8000-10,000 acres.

WORLD AND UNITED STATES KIWIFRUIT PRODUCTION

A. World – 1987 data.

Country Acres Production (tons)

New Zealand 39,200 210,000
Italy 31,700 91,000
Japan 10,800 38,000
USA (California) 8,700 27,000
France 10,400 22,000
Australia 2,500 9,000
Greece 4,200 4,000
Chile 12,400 3,000
All Other 6,100 8,000

World total 126,000 412,000

New Zealand – 539 million $NZ ($270 million US) in kiwi exports in 1990.

B. United States – Very few commercial plantings outside of California.

California – 38,636 MT on 7000 acres in 1995; value 18 million. Acreage is stable, but production down 10-20% in last 3 years.

For the most up to date statistical data on United States and World production numbers please refer to the following two websites:

World: The Food and Agriculture Organization of the United Nations Statistics Division (FAOSTAT). FAOSTAT

United States: The United States Department of Agriculture National Agricultural Statistics Service (USDA Ag Stats). USDA Ag Stats

KIWIFRUIT BOTANICAL DESCRIPTION

A. Plant: Kiwifruit vines are extremely vigorous and long-lived, bearing fruit for 50 years or more. Trunks may become 8 inches in diameter in mature plantings. Two types of shoots are produced – terminating and non-terminating. The former are short, 3-6 leaved shoots, which frequently form flower buds the following year. Non-terminating shoots may grow 10-15 ft in a season, producing smaller leaves along long internodes, with the distal portion of the shoot often coiling on contact with other shoots or solid objects. Non-terminating shoots perform the function of tendrils, which are absent in kiwi. Leaves are large (8″ diameter), round, petioled, with entire margins, and light pubescence on the underside.

B. Flower: Relatively large (1-2 inch diameter), white changing to golden-yellow, flowers are borne on long peduncles in axils of leaves on current season’s growth. Although flowers are produced in few-flowered cymes, most lateral flowers do not develop, giving 1 flower per axil. A whorl of many stamens surrounds the ovary, although they are smaller and produce non-viable pollen in pistillate flowers.

Female flowers have 30 styles fused at the base into a superior ovary with the same # of carpels; each carpel contains 10-20 ovules. These flowers are usually larger than males.

Male flowers have rudimentary ovaries and reduced styles, but a pronounced whorl of many stamens which are longer than in flowers. Rarely, these flowers set very small fruit, indicating that a self-fruitful, hermaphroditic cultivar could be developed in the future.

Flower buds appear shortly after budbreak, but anthesis is delayed about 2 months since flower development takes place entirely in spring.

C. Pollination: Bees are the primary pollinator for kiwifruit. For adequate fruit size, 900-1300 seeds must be set in each fruit (fruit size is proportional to seed content), requiring the deposition of several thousand pollen grains to the female flowers.

Ratios of 8:1 or 6:1 (female:male) are optimal, but male vines are pruned more severely to occupy 10% of the canopy. Males are sometimes trained above female vines to allow easier access by bees. High densities of bees (3 hives/acre) are necessary to encourage foraging and female visitation, since females produce no pollen or nectar to attract bees; low densities of bees will favor males exclusively.

D. Fruit: The fruit is a many-seeded berry with a brown, hispid exocarp (peel). The flesh is green due to chlorophyll, which (atypically!) does not degrade during ripening. The core or central axis is white, edible, having 1-3 rows of small black seeds radiating around it. There is no fruit drop in kiwi; all fruit that set will mature. However, mature vines which have not been pruned enough, must be thinned for adequate size development. Optimally, fruit are thinned to 40-45 per yd2 of canopy, if pruning has not reduced crop load sufficiently.

KIWIFRUIT GENERAL CULTURE

A. Soils and Climate:

Soils. Light, well-drained, deep soils with fairly high organic matter are best. Heavy clays and calcareous soils should be avoided, pH should be mildly acid, 6.0. Kiwi vines are very sensitive to both flooding and water deficit; irrigation is necessary even in humid climates.

Climate. The native habitat of kiwifruit is the warm, humid, temperate regions of southeast China. Rainfall is abundant (50-70 inches) and humidity high throughout the year. Winter temperatures may reach -15°C, and the topsoil may freeze. Vines are sheltered from wind by the forest canopies into which they grow.

Wind is a major problem in kiwi culture. High winds during storms can break shoots off arms, knock fruit off or cause surface blemishes (“wind rub”), and stunt growth of young vines. Natural or artificial windbreaks must be used.

Frost in spring and fall is a problem in marginal areas, since kiwifruit require 220 day growing season (ca. 160 days from bloom maturity).

Chilling requirement is relatively short, 500 hr, allowing culture in southern California, and on the southeastern coastal plain.

B. Propagation: Rooted cuttings (semi-hardwood) are most often used. Terminal shoots with 2 leaves are taken in mid/late summer, and rooted under mist with 2000-5000 ppm IBA. Leaves are cut in half to reduce transpiration. Rooting takes place in 2-4 weeks.

C. Rootstocks: None

D. Orchard design, pruning, training:

Design/Training. Vines are trained to either pergolas, where the entire ground surface is covered by continuous overhead canopy, or T-bar trellises, where room for equipment operation between rows is provided. Pollenizers are distributed throughout the planting so that every female is adjacent to a male (8:1).

Pruning. Pruning not only reduces vine tangling and thickness, but regulates crop load as balanced pruning of grapes. Whether T-bar or Pergola, vines are basically bilateral cordons, with only trunks and arms being permanent wood. Dormant and summer pruning are used to control the extreme vigor. Male cultivars are pruned immediately after flowering.

THE KIWI’S CONTRIBUTION TO DIET

Kiwifruit are utilized almost exclusively as fresh fruits, with the exception of a small proportion juiced and mixed with other juices and used in wine coolers. Fruit are also canned and frozen for long-term storage. In New Zealand, wine, jam, and other products are made from fresh fruits. Kiwi goes well with avocado, raddichio and endive, and can be used in seafood, chicken, ham, or duck dishes with ginger dressings (Elizabeth Schneider).

Due to chlorophyll content, the juice becomes a “sludgy, olive-green color” when squeezed, as chlorophyll breaks down and is oxidized. For this reason, juice is not a major product.

Fruits contain high quantities of proteolytic enzymes like actinidin (similar to papain in papaya), and can be used to tenderize meat and prevent gelatin-based jellies from setting.

Kiwifruit are one of the richest sources of vitamin C available; a single fruit contains enough to satisfy the minimum daily requirement.

Dietary value, per 100 gram edible portion:

Water (%) …………………………………. 90 (?)
Calories …………………………………….. 56
Protein (%) ………………………………….. 1.0
Fat (%) ………………………………………… —
Carbohydrates (%) ……………………. 12
Crude Fiber (%) ………………………….. ?

% of US RDA*

Vitamin A ………………………………….. ?
Thiamin, B1 ……………………………….. ?
Riboflavin, B2 ……………………………. ?
Niacin ………………………………………… ?
Vitamic C ………………………………….. 233
Calcium ……………………………………… 4.6
Phosphorus ………………………………. 2.9
Iron …………………………………………… 9.0
Sodium ……………………………………… —
Potassium …………………………………. 7.2

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* Percent of recommended daily allowance set by FDA, assuming a 154 lb male adult, 2700 calories per day.