Avocado

The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family ( Lauraceae). It is native to the Americas and was first domesticated by Mesoamerican tribes more than 5,000 years ago. Then as now it was prized for its large and unusually oily fruit. The tree likely originated in the highlands bridging south-central Mexico and Guatemala. Its fruit, sometimes also referred to as an alligator or avocado pear, is botanically a large berry containing a single large seed. Avocado trees are partially self-pollinating, and are often propagated through grafting to maintain consistent fruit output. Avocados are presently cultivated in the tropical and Mediterranean climates of many countries. Mexico is the world's leading producer of avocados as of 2020, supplying nearly 30% of the global harvest in that year.

The fruit of domestic varieties have smooth, buttery, golden-green flesh when ripe. Depending on the cultivar, avocados have green, brown, purplish, or black skin, and may be pear-shaped, egg-shaped, or spherical. For commercial purposes the fruits are picked while immature and ripened after harvesting. The nutrient density and extremely high fat content of avocado flesh are useful to a variety of cuisines and are often eaten to enrich vegetarian diets.

In major production regions like Chile, Mexico and California the water demands of avocado farms place strain on local sources. Avocado production is also implicated in other externalities, including deforestation and human rights concerns associated with the partial control of their production in Mexico by organized crime. Global warming is expected to result in significant changes to the suitable growing zones for avocados, and place additional pressures on the locales in which they are produced due to heat waves and drought.

Botany

''Persea americana'' is a tree that grows to , with alternately arranged leaves long. Panicles of flowers with deciduous bracts arise from new growth or the axils of leaves. The flowers are inconspicuous, greenish-yellow, wide.

The species is variable because of selection pressure by humans to produce larger, fleshier fruits with a thinner exocarp. The avocado fruit is a climacteric, single-seeded berry, due to the imperceptible endocarp covering the seed, rather than a drupe. The pear-shaped fruit is usually long, weighs between , and has a large central seed, long.

History

''Persea americana'', or the avocado, possibly originated in the Tehuacan Valley in the state of Puebla, Mexico, although fossil evidence suggests similar species were much more widespread millions of years ago. However, there is evidence for three possible separate domestications of the avocado, resulting in the currently recognized Mexican (''aoacatl''), Guatemalan (''quilaoacatl''), and West Indian (''tlacacolaocatl'') landraces. The Mexican and Guatemalan landraces originated in the highlands of those countries, while the West Indian landrace is a lowland variety that ranges from Guatemala, Costa Rica, Colombia, Ecuador to Peru, achieving a wide range through human agency before the arrival of the Europeans. The three separate landraces were most likely to have already intermingled in pre-Columbian America and were described in the Florentine Codex.

The earliest residents of northern coastal Peru were living in temporary camps in an ancient wetland and eating avocados, along with chilies, mollusks, sharks, birds, and sea lions. The oldest discovery of an avocado pit comes from Coxcatlan Cave, dating from around 9,000 to 10,000 years ago. Other caves in the Tehuacan Valley from around the same time period also show early evidence for the presence and consumption of avocado. There is evidence for avocado use at Norte Chico civilization sites in Peru by at least 3,200 years ago and at Caballo Muerto in Peru from around 3,800 to 4,500 years ago.

The native, undomesticated variety is known as a ''criollo'', and is small, with dark black skin, and contains a large seed. It probably coevolved with extinct megafauna. In 1982, evolutionary biologist Daniel H. Janzen concluded that the avocado is an example of an "evolutionary anachronism", a fruit adapted for ecological relationship with now-extinct large mammals (such as giant ground sloths or gomphotheres). Most large fleshy fruits serve the function of seed dispersal, accomplished by their consumption by large animals. There are some reasons to think that the fruit, with its mildly toxic pit, may have coevolved with Pleistocene megafauna to be swallowed whole and excreted in their dung, ready to sprout. No extant native animal is large enough to effectively disperse avocado seeds in this fashion.

The avocado tree also has a long history of cultivation in Central and South America, likely beginning as early as 5,000 BC. 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 (''circa'' 1470–1528) in 1519 in his book, ''Suma De Geographia Que Trata De Todas Las Partidas Y Provincias Del Mundo.'' The first detailed account that unequivocally describes the avocado was given by Gonzalo Fernández de Oviedo y Valdés in his work in 1526. The first written record in English of the use of the word 'avocado' was by Hans Sloane, who coined the term, in a 1696 index of Jamaican plants. The plant was introduced to Spain in 1601, Indonesia around 1750, Mauritius in 1780, Brazil in 1809, the United States mainland in 1825, South Africa and Australia in the late 19th century, and the Ottoman Empire in 1908. In the United States, the avocado was introduced to Florida and Hawaii in 1833 and in California in 1856.

Before 1915, the avocado was commonly referred to in California as ''ahuacate'' and in Florida as ''alligator pear''. In 1915, the California Avocado Association introduced the then-innovative term ''avocado'' to refer to the plant.

Etymology

The word ''avocado'' comes from the Spanish , which derives from the Nahuatl (Mexican) word , which goes back to the proto-Aztecan . In Molina's Nahuatl dictionary "auacatl" is given also as the translation for ''compañón'' "testicle", and this has been taken up in popular culture where a frequent claim is that testicle was the word's original meaning. This is not the case, as the original meaning can be reconstructed rather as "avocado" - rather the word seems to have been used in Nahuatl as a euphemism for "testicle".

The modern English name comes from a rendering of the Spanish as . The earliest known written use in English is attested from 1697 as ''avogato pear'', later ''avocado pear'' (due to its shape), a term sometimes corrupted to ''alligator pear''.

Regional names

In Central American, Caribbean Spanish-speaking countries, and Spain it is known by the Mexican Spanish name , while South American Spanish-speaking countries Argentina, Chile, Perú and Uruguay use a Quechua-derived word, . In Portuguese, it is . The Nahuatl can be compounded with other words, as in , meaning avocado soup or sauce, from which the Spanish word derives.

In the United Kingdom the term ''avocado pear'', applied when avocados first became commonly available in the 1960s, is sometimes used.

Originating as a diminutive in Australian English, a clipped form, ', has since become a common colloquialism in South Africa and the United Kingdom.

It is known as "butter fruit" in parts of India and Hong Kong.

Cultivation

As a subtropical species, avocados need 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. Several cold-hardy varieties are planted in the region of Gainesville, Florida, which survive temperatures as low as with only minor leaf damage. The trees also need well-aerated soils, ideally more than 1 m deep. However, Guatemalan varieties such as "MacArthur," "Rincon", or "Nabal" can withstand temperatures down to 29 F.

According to information published by the Water Footprint Network, it takes an average of approximately of applied fresh ground or surface water, not including rainfall or natural moisture in the soil, to grow one avocado (). However, the amount of water needed depends on where it is grown; for example, in the main avocado-growing region of Chile, about of applied water are needed to grow one avocado ().

Increasing demand and production of avocados may cause water shortages in some avocado production areas, such as the Mexican state of Michoacán. Avocados may also cause environmental and socioeconomic impacts in major production areas, illegal deforestation, and water disputes. Water requirements for growing avocados are three times higher than for apples, and 18 times higher than for tomatoes.

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.

Like the banana, the avocado is a climacteric fruit, which matures on the tree, but ripens off the tree. Avocados used in commerce are picked hard and green and kept in coolers at 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' 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 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 by 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. The two flowering types are 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''. Advances in cloning techniques that can produce up to 500 new plants from a single millimetre of tree cutting have the potential to increase the availability of rootstocks.

Commercial avocado production is limited to a small fraction of the vast genetic diversity in the species. Conservation of this genetic diversity has relied largely on field collection, as avocado seeds often do not survive storage in seed banks. This is problematic, as field preservation of living cultivars is expensive, and habitat loss threatens wild cultivars. More recently, an alternate method of conservation has been developed based on cryopreservation of avocado somatic embryos with reliable methods for somatic embryogenesis and reconstitution into living trees.

As a houseplant

The avocado tree can be grown domestically and used as a decorative houseplant. The pit germinates in normal soil conditions or partially submerged in a small glass (or container) of water. In the latter method, the pit sprouts in four to six weeks, at which time it is planted in standard houseplant potting soil. The plant normally grows large enough to be prunable; it does not bear fruit unless it has ample sunlight. Home gardeners can graft a branch from a fruit-bearing plant to speed maturity, which typically takes four to six years to bear fruit.

Pests and 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. The pyriform scale insect (''Protopulvinaria pyriformis'') is known from Australia, South Africa, Israel, Italy, France, Spain, Cuba, Florida, and Peru. It is normally found on avocado, and in Peru it is said to be the worst insect pest of the fruit. Certain cultivars of avocado seem more susceptible to attack by the scale than others.

Cultivation by location

Cultivation in Mexico

Mexico is by far the world's largest avocado growing country, producing several times more than the second largest producer. In 2013, the total area dedicated to avocado production was 188,723 hectares (415,520 acres), and the harvest was 2.03 million tonnes in 2017. The states that produce the most are México, Morelos, Nayarit, Puebla, and Michoacan, accounting for 86% of the total. In Michoacán, the cultivation is complicated by the existence of drug cartels that extort protection fees from cultivators. They are reported to exact 2,000 Mexican pesos per hectare from avocado farmers and 1 to 3 pesos/kg of harvested fruit. It is such a problem that the phrase ''blood guacamole,'' has been adopted to describe the social effects in Mexico of the vast worldwide demand for its fruits.

Cultivation in California

The avocado was introduced from Mexico to California in the 19th century, and has become a successful cash crop. About – as of 2015, some 80% of United States avocado production – is located in Southern California,Sternbergh, Adam, "Avocados Are Toast," New York magazine, April 20 - May 3, 2015 with 60% in San Diego County.

Avocado is the official fruit of the state of California. Fallbrook, California, claims, without official recognition, the title of "Avocado Capital of the World" (also claimed by the town of Uruapan in Mexico), and both it and Carpinteria, California, host annual avocado festivals.

The California Avocado Commission and the California Avocado Society are the two major grower organizations and Calavo Growers is a major distributor.

Cultivation in Peru

'Hass' avocado production in Peru encompasses thousands of hectares in central and western Peru. Peru has now become the largest supplier of avocados imported to the European Union and the second largest supplier to Asia and the United States. The country's location near the equator and along the Pacific Ocean creates consistently mild temperatures all year.

'Hass' avocados from Peru are seasonally available to consumers from May through September and are promoted under the auspices of the Peruvian Avocado Commission, headquartered in Washington, D.C.

Cultivation in Chile

Chile has produced avocados for over 100 years with production increasing dramatically in the early 1980s due to global demand. ''New York'' magazine reported in 2015 that "Large avocado growers are draining the country's groundwater and rivers faster than they can replenish themselves." 88% of total production and 99% of exported avocados from Chile are Hass avocados. Avocados are a staple fruit in Chile with 30% of production destined for the domestic market. The country pays zero important tariffs with the China, United States, and the European Union, due to free trade agreements.

Cultivars

A cultivars

* 'Choquette': A seedling from Miami, Florida. 'Choquette' bore large fruit of good eating quality in large quantities and had good disease resistance, and thus became a major cultivar. Today 'Choquette' is widely propagated in south Florida both for commercial growing and for home growing.
* 'Gwen': A seedling bred from 'Hass' x 'Thille' in 1982, 'Gwen' is higher yielding and more dwarfing than 'Hass' in California. The fruit has an oval shape, slightly smaller than 'Hass' (), with a rich, nutty flavor. The skin texture is more finely pebbled than 'Hass', and is dull green when ripe. It is frost-hardy down to .
* 'Hass': The 'Hass' is the most common cultivar of avocado. It produces fruit year-round and accounts for 80% of cultivated avocados in the world. All 'Hass' trees are descended from a single "mother tree" raised by a mail carrier named Rudolph Hass, of La Habra Heights, California. Hass patented the productive tree in 1935. The "mother tree", of uncertain subspecies, died of root rot and was cut down in September 2002."Avocado Tree's Demise Is the Pits for Growers; Fitting farewell sought for 'mother'"
Los Angeles Times, 7 September 2003.
* 'Lula': A seedling reportedly grown from a 'Taft' avocado planted in Miami on the property of George Cellon, it is named after Cellon's wife, Lula. It was likely a cross between Mexican and Guatemalan types. 'Lula' was recognized for its flavor and high oil content and propagated commercially in Florida.
* 'Maluma': A relatively new cultivar, it was discovered in South Africa in the early 1990s by Mr. A.G. (Dries) Joubert. It is a chance seedling of unknown parentage.
* 'Pinkerton': First grown on the Pinkerton Ranch in Saticoy, California, in the early 1970s, 'Pinkerton' is a seedling of 'Hass' x 'Rincon'. The large fruit has a small seed, and its green skin deepens in color as it ripens. The thick flesh has a smooth, creamy texture, pale green color, good flavor, and high oil content. It shows some cold tolerance, to and bears consistently heavy crops. A hybrid Guatemalan type, it has excellent peeling characteristics.
* 'Reed': Developed from a chance seedling found in 1948 by James S. Reed in California, this cultivar has large, round, green fruit with a smooth texture and dark, thick, glossy skin. Smooth and delicate, the flesh has a slightly nutty flavor. The skin ripens green. A Guatemalan type, it is hardy to . Tree size is about .

B cultivars

* 'Sharwil': Developed by James Cockburn Wilson (died 1990) with Frank Victor Sharpe in Tamborine Mountain, Queensland, Australia in the 1950s, a portmanteau

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