Avocado

Avocado (Persea americana) is a tree native to Mexico and Central America, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel. Avocado or alligator pear also refers to the fruit, botanically a large berry that contains a single seed.

Avocados are commercially valuable and are cultivated in tropical and Mediterranean climates throughout the world. They have a green-skinned, fleshy body that may be pear-shaped, egg-shaped, or spherical. Commercially, they ripen after harvesting. Trees are partially self-pollinating and often are propagated through grafting to maintain a predictable quality and quantity of the fruit.


History


Persea americana, or the avocado, originated in the state of Puebla, Mexico. The native, undomesticated variety is known as a criollo, and is small, with dark black skin, and contains a large seed. It likely coevolved with extinct megafauna. The oldest evidence of avocado use was found in a cave located in Coxcatlán, Puebla, Mexico, that dates to around 10,000 BC. The avocado tree also has a long history of cultivation in Central and South America; a water jar shaped like an avocado, dating to AD 900, was discovered in the pre-Incan city of Chan Chan. The earliest known written account of the avocado in Europe is that of Martín Fernández de Enciso (c.1470–c.1528) in 1518 or 1519 in his book, Suma De Geographia Que Trata De Todas Las Partidas Y Provincias Del Mundo. The first written record in English of the use of the word 'avocado' was by Hans Sloane in a 1696 index of Jamaican plants. The plant was introduced to Indonesia in 1750, Brazil in 1809, the Levant in 1908, and South Africa and Australia in the late 19th century.


Etymology


The word "avocado" comes from the Spanish aguacate which in turn comes from the Nahuatl word āhuacatl [aːˈwakat͡ɬ], which goes back to the proto-Aztecan *pa:wa with the same meaning. In some countries of South America, such as Argentina, Bolivia, Chile, Peru, and Uruguay, the avocado is known by its Quechua name, palta. In other Spanish-speaking countries it is known by the Mexican name and in Portuguese it is abacate. The fruit is sometimes called an avocado pear or alligator pear (due to its shape and the rough green skin of some cultivars). The Nahuatl ahuacatl can be compounded with other words, as in ahuacamolli, meaning avocado soup or sauce, from which the Spanish word guacamole derives.

The modern English name is not etymologically related to the similar sounding Spanish word abogado, meaning 'lawyer' (as in advocate), but comes through an English rendering of the Spanish "aguacate" as "avogato". The earliest known written use in English is attested from 1697 as "Avogato Pear", a term which was later corrupted as "alligator pear". Because the word avogato sounded like "advocate" several languages reinterpreted it to have that meaning and "advocate"-forms of the word appear in several other Germanic languages, such as the German Advogato-Birne, the Swedish advokatpäron, the old Danish advokat-pære (today it is called "avocado") and the Dutch advocaatpeer. It is known as "butter fruit" in parts of India. In eastern China it is known as è lí (鳄梨, a direct translation of "alligator pear") or huángyóu guǒ (黄油果, "butter fruit").


Cultivation


The tree grows to 20 m (66 ft), with alternately arranged leaves 12 centimetres (4.7 in) – 25 centimetres (9.8 in) long. The flowers are inconspicuous, greenish-yellow, 5 millimetres (0.2 in) – 10 millimetres (0.4 in) wide. The pear-shaped fruit is 7 centimetres (2.8 in) – 20 centimetres (7.9 in) long, weighs between 100 grams (3.5 oz) – 1,000 grams (35 oz), and has a large central seed, 5 centimetres (2.0 in) – 6.4 centimetres (2.5 in) long.

The subtropical species needs a climate without frost and with little wind. High winds reduce the humidity, dehydrate the flowers, and affect pollination. When even a mild frost occurs, premature fruit drop may occur, although the Hass cultivar 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 is highly saline. These soil and climate conditions are available only in a few areas of the world, particularly in southern Spain, Portugal, Morocco, Crete, the Levant, South Africa, Colombia, Peru, parts of central and northern Chile, Vietnam, Indonesia, parts of southern India, Sri Lanka, Australia, New Zealand, the Philippines, Malaysia, Central America, the Caribbean, Mexico, California, Arizona, Puerto Rico, Texas, Florida, Hawaii, Ecuador and Rwanda. Each region has different types of cultivars.


Harvest and postharvest


Commercial orchards produce an average of seven tonnes per hectare each year, with some orchards achieving 20 tonnes per hectare.Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next. The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates. There are several cold-hardy varieties planted in the region of Gainesville, Florida, which survive temperatures as low as −6.5 °C (20 °F) with only minor leaf damage.

The avocado is a climacteric fruit (the banana is another), which means it matures on the tree, but ripens off the tree. Avocados used in commerce are picked hard and green and kept in coolers at 3.3 to 5.6 °C (38 to 42 °F) until they reach their final destination. Avocados must be mature to ripen properly. Avocados that fall off the tree ripen on the ground. Generally, the fruit is picked once it reaches maturity; Mexican growers pick Hass-variety avocados when they have more than 23% dry matter, and other producing countries have similar standards. Once picked, avocados ripen in one to two weeks (depending on the cultivar) at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas). Some supermarkets sell pre-ripened avocados which have been treated with synthetic ethylene to hasten ripening. The use of an ethylene gas "ripening room", which is now an "industry standard," was pioneered in the 1980s by farmer Gil Henry of Escondido, California, in response to footage from a hidden supermarket camera which showed shoppers repeatedly squeezing hard, unripe avocados, putting them "back in the bin," and moving on without making a purchase. In some cases avocados can be left on the tree for several months, which is an advantage to commercial growers who seek the greatest return for their crop; but if the fruit remains unpicked for too long it falls to the ground.


Breeding


The species is only partially able to self-pollinate because of dichogamy in its flowering. This limitation, added to the long juvenile period, makes the species difficult to breed. Most cultivars are 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 for programs at the University of California, Riverside, as well as the Volcani Centre and the Instituto de Investigaciones Agropecuarias in Chile.

The avocado is unusual in that the timing of the male and female flower phases differs among cultivars. There are two flowering types, "A" and "B". "A" cultivar flowers open as female on the morning of the first day and close in late morning or early afternoon. Then they open as male in the afternoon of the second day. "B" varieties open as female on the afternoon of the first day, close in late afternoon and reopen as male the following morning.

"A" cultivars: Hass, Gwen, Lamb Hass, Pinkerton, Reed.
"B" cultivars: Fuerte, Sharwil, Zutano, Bacon, Ettinger, Sir Prize, Walter Hole.

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. In addition, due to environmental circumstances during some years, seedless avocados may appear on the trees. Known in the avocado industry as "cukes", they are usually discarded commercially due to their small size.


Propagation and rootstocks


Avocados can be propagated by seed, taking roughly four to six years to bear fruit, although in some cases seedlings can take 10 years to come into bearing. The offspring is unlikely to be identical to the parent cultivar in fruit quality. Prime quality varieties are therefore propagated by grafting to rootstocks that are propagated by seed (seedling rootstocks) or by layering (clonal rootstocks). After about a year of growing in a greenhouse, the young rootstocks are ready to be grafted. Terminal and lateral grafting is normally used. The scion cultivar grows for another 6–12 months before the tree is ready to be sold. Clonal rootstocks are selected for tolerance of specific soil and disease conditions, such as poor soil aeration or resistance to the soil-borne disease (root rot) caused by Phytophthora.


Growing indoors


Usually, avocados are grown from pits indoors. This is often done by removing the pit from a ripe, unrefrigerated avocado. The pit is then stabbed with three or four tooth picks, about one third of the way up. The pit is placed in a jar or vase containing tepid water. It should split in four to six weeks and yield roots and a sprout. If there is no change by this time, the avocado pit is discarded. Once the stem has grown a few inches, it is placed in a pot with soil. It should be watered every few days. Avocados have been known to grow large, so owners must be ready to repot the plant several times.


Diseases


Avocado trees are vulnerable to bacterial, viral, fungal and nutritional diseases (excesses and deficiencies of key minerals). Disease can affect all parts of the plant, causing spotting, rotting, cankers, pitting and discoloration.


Cultivation in California


The avocado was introduced from Mexico to California in the 19th century, and has become a successful cash crop. About 59,000 acres (240 km2) – some 95% of United States avocado production – is located in Southern California, with 60% in San Diego County.Fallbrook, California, claims the title of "Avocado Capital of the World" (also claimed by the town of Uruapan, Michoacán, México), and both Fallbrook and Carpinteria, California, host annual avocado festivals.


Cultivation in Mexico


Mexico produces most of the world's avocado, and avocado is one of the primary cultivars for export, the eighth cultivar by production volume. In 2013 the total area dedicated to avocado production was 168,155 hectares (415,520 acres), and the harvest was of 1,109,814 tonnes. The states that produce the most are México, Morelos, Nayarit og Puebla, and Michoacan which accounts for 86% of the total. In Michoacan the cultivation is complicated by the existence of drug cartels that extort protection fees from cultivators. They are reported to exact 2000 Mexican pesos per hectar from avocado farmers and an additional 1 to 3 pesos per kilo of harvested fruit.


Other cultivars


Other avocado cultivars include Spinks. The fruit of the cultivar Florida, grown mostly outside 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. Historically attested varieties (which may or may not survive among Horticulturists) include the Challenge, Dickinson, Kist, Queen, Rey, Royal, Sharpless, and Taft.


Avocado-related international trade issues


After the North American Free Trade Agreement (NAFTA) went into effect in 1994, Mexico tried exporting avocados to the US. The US government resisted, claiming the trade would introduce Tephritidae fruit flies that would destroy California's crops. The Mexican government responded by inviting USDA inspectors to Mexico, but the U.S. government declined, claiming fruit fly inspection was not feasible. The Mexican government then proposed to sell avocados only to the northeastern US in the winter (fruit flies cannot withstand extreme cold). The US government balked, but gave in when the Mexican government started erecting barriers to US corn.

Another argument is that the lower prices generated by Mexican (and Chilean) imports would increase the popularity of avocados outside of California, thereby assuaging the loss of profits due to the new competition[original research?].

Today, avocados from Mexico are allowed throughout the US, because USDA inspectors in Michoacán (where 90% of Hass avocados from Mexico are grown) inspected fruit in Uruapan. Imports from Mexico in the 2005–2006 season exceeded 130,000 metric tons (143,300 short tons; 127,900 long tons).

In 2009, Peru joined Chile and Mexico as an exporter of avocados to the US.

In the US avocados are grown in California and Florida, where land, labor and water are expensive. Avocado trees require frequent, deep watering to bear optimally, particularly in spring, summer, and fall. Due to increased Southern Californian water costs, they are now costly to grow. California produces 90% of the United States' avocados.

As of 2013, Mexico leads international exports, with other significant production in California, New Zealand, Peru and South Africa.


Thanks to wikipedia.org

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