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Cultivation

      This subtropical species needs a climate without frost and not too much wind. When a frost event does happen, the fruit drops from the tree, reducing the yield. The cultivar 'Hass' can tolerate temperatures down to -1 C. The trees also need well aerated soils, ideally more than 1 m deep. Yield is reduced when the irrigation water has a high electrical conductivity. These soil and climatate conditions are met only in a few areas of the world, especially in Spain, Israel, South Africa, Chile, Australia, New Zealand and logically in Mexico, the center of origin and diversity of this species. In the U.S. avocados are produced commercially only in California and Florida, eventhough the varieties used are different.

Propagation and rootstocks

      While an avocado propagated by seed can bear fruit, it will take 4-6 years to do so, and the offspring is unlikely to resemble the parent cultivar in fruit quality. Thus, commercial orchards are planted using grafted trees and rootstocks. Rootstocks are propagated by seed (seedling rootstocks) and also layering (clonal rootstocks). After about 1 year of growing the young plants in a greenhouse, they are ready to be grafted. Terminal and lateral grafting is normally used. The scion cultivar will then grow for another 6-12 months before the tree is ready to be sold. Clonal rootstocks have been selected for specific soil and disease conditions, such as poor soil aeration or resistance to the soil borne disease caused by Phytophthora root rot.

Breeding

      The species is partially unable to self-pollinate, because of dichogamy in its flowering. The limitation, added to the long juvenile period, make it difficult to breed this species. Most cultivars are clonally propagated (via grafting), having originated from random seedling plants or minor mutations derived from cultivars. Modern breeding programs tend to use isolation plots where the chances of cross-pollination are reduced. That is the case of programs at the University of California-Riverside, as well as the Volcani Centre in Israel.

Harvest and post-harvest

      The avocado fruit does not ripen on the tree, but will fall off or be picked in a hard, "green" state, then it will ripen quickly on the ground, but depending on the amount of oil that it has the taste may be very different. Generally, the fruit is picked once it reaches a mature size, and will then ripen in a few days (faster if stored with other fruit such as bananas, because of the influence of ethylene gas). Premium supermarkets sell pre-soften avocados, treated with a special gas to stimulate ethylene synthesis in the fruit (the same process used to de-green lemons). The fruit can be left on the tree until required, rather than picked and stored, but for commercial reasons it must be picked as soon as possible. Growers can keep the fruit on the tree for about 4-6 months after fully developed; if the fruit stays on the tree for too long it will fall to the ground.

Introduction to Europe

      The earliest known account of the avocado in Europe is that of Martin Fernandez De Encisco in 1519. The plant was first introduced to Indonesia by 1750, Brazil in 1809, Palestine in 1908, and South Africa and Australia in the late 19th century. (Source: indexfresh.com).

Cultivation in California

      The avocado was introduced to the U.S. state of California in the 19th century, and it has become an extremely successful cash crop. 95% of United States avocado production is located in California, and 80% occurs in San Diego County. Approximately 59,000 acres (approximately 24,000 hectares) of avocados are grown in California. Fallbrook, California claims the title of "Avocado Capital of the World" and hosts an annual Avocado Festival.

      While dozens of cultivars are grown in California, 'Hass' (usually misspelled 'Haas') is most common, accounting for more than 80% of the crop. In appearance, Hass has a dark, rippled skin and rich, creamy flesh. All Hass avocado trees are related to a single "mother tree" that was purchased as a seedling by a mail carrier named Rudolph Hass. He purchased the tree as a seedling from A.R. Rideout of Whittier, California, in 1926. Hass planted the seedling in his front yard in La Habra Heights, California, and patented the tree in 1935. All Hass avocados can be traced back to grafts made from that tree. The "Mother Tree" died of root rot in 2002. Other avocado cultivars include 'Bacon', 'Fuerte' (pictured), 'Gwen', 'Pinkerton', 'Reed' and 'Zutano'. The fruit of the cultivar 'Florida', grown mostly outside of California, is larger and rounder, with a smooth, medium-green skin, and a less-fatty, firmer and fibrous flesh. These are occasionally marketed as low-calorie avocados.

      The avocado is unusual in that the timing of the male and female phases differs among cultivars. There are two flowering types, referred to as "A" and "B" flower types. "A" cultivars open as female on the morning of the first day. The flower closes in late morning or early afternoon. The flower will remain closed until the afternoon of the second day when it opens as male. "B" varieties open as female on the afternoon of the first day, close in late afternoon and re-open in the male phase the following morning.

      Certain cultivars, such as the 'Hass', have a tendency to bear well only in alternate years. After a season with a low yield, due to factors such as cold (which the avocado does not tolerate well), the trees tend to produce abundantly the next season. This heavy crop depletes stored carbohydrates, resulting in a reduced yield the following season, and thus the alternate bearing pattern becomes established.

As a houseplant

      Avocado can be grown as a houseplant from seed, eventhough it will not normally bear fruit indoors; people enjoy it for its greenery. It can be germinated in normal soil in a large pot, or in a glass of water with a piece of charcoal for deodorizing, with the top half held up by toothpicks.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Avocado".