Persea americana (*)
Persea americana Mill.
* Gard. dict. ed. 8: Persea no. 1. 1768
The avocado (Persea americana) is a tree native to Puebla, Mexico, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel. Avocado or alligator pear also refers to the fruit (a large berry that contains a large seed) of the tree, which may be pear-shaped, egg-shaped or spherical.
Avocados are a commercially valuable fruit and are cultivated in tropical climates throughout the world (and some temperate ones, such as California), producing a green-skinned, pear-shaped fruit that ripens after harvesting. Trees are partially self-pollinating and often are propagated through grafting to maintain a predictable quality and quantity of the fruit.
P. 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. 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.
The word 'avocado' comes from the Nahuatl word ahuacatl (testicle, a reference to the shape of the fruit). Avocados were known by the Aztecs as 'the fertility fruit'. 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 called aguacate, 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 Mexican Spanish word guacamole derives.. It is known as Butter Fruit in parts of India. 
The tree grows to 20 m (69 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, Crete, the Levant, South Africa, 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, New Mexico, Texas, Florida and Ecuador. Each region has different types of cultivars. Mexico, the center of origin and diversity of this species, is the largest producer of the Hass variety, with over one million tonnes produced annually.
Harvest and postharvest
An average avocado tree produces about 1,200 avocados annually. Commercial orchards produce an average of seventonnes 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.
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 a few days at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas). Premium supermarkets sell preripened avocados treated with synthetic ethylene to hasten the ripening process. 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; if the fruit remains unpicked for too long, however, it falls to the ground.
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.
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
While an avocado propagated by seed can bear fruit, it takes roughly four to six years to do so, and the offspring is unlikely to resemble the parent cultivar in fruit quality. Rootstocks are propagated by seed (seedling rootstocks) and also layering (clonal rootstocks). After about a year of growing in a greenhouse, the young plants 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 have been selected for specific soil and disease conditions, such as poor soil aeration or resistance to the soil-borne disease (root rot) caused by Phytophthora.
Often, 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 with tepid water. In four to six weeks, it should split and out should come 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.
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 the U.S state of California in the 19th century, and has become an extremely successful cash crop. About 59,000 acres (24,000 hectares) – 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", and both Fallbrook and Carpinteria, California host annual avocado festivals.
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 horticulturalists) 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.
Today, avocados from Mexico are allowed in all 50 states, because USDA inspectors in Michoacán (where 90% of Hass avocados from Mexico are grown), have cut open and inspected millions of fruit in Uruapan, and found no problems. Imports from Mexico in the 2005–2006 season exceeded 130,000 tonnes.[clarification needed]
In 2009, Peru joined Chile and Mexico as an exporter of avocados to the US.
Avocados once were more expensive in the US than in most other countries, because those consumed in the US were grown almost exclusively in California and Florida, where land, labor and water are expensive. The avocado tree requires frequent, deep watering to bear optimal amounts of fruit, particularly in spring, summer, and fall; and due to the increased costs for water in Southern California versus those of prior decades, it is now a costly crop to grow. California produces about 90% of the United States' avocado crop.
Internationally, avocado exports are dominated by Mexico.
The fruit of horticultural cultivars has a markedly higher fat content than most other fruit, mostly monounsaturated fat, and as such serves as an important staple in the diet of various groups where access to other fatty foods (high-fat meats and fish, dairy, etc.) is limited.
A ripe avocado yields to gentle pressure when held in the palm of the hand and squeezed. The flesh is prone to enzymatic browning; it turns brown quickly after exposure to air. To prevent this, lime or lemon juice can be added to avocados after they are peeled.
The fruit is not sweet, but fatty, and distinctly yet subtly flavored, and of smooth, almost creamy texture. It is used in both savory and sweet dishes, though in many countries not for both. The avocado is very popular in vegetarian cuisine, as substitute for meats in sandwiches and salads because of its high fat content.
Generally, avocado is served raw, though some cultivars, including the common Hass, can be cooked for a short time without becoming bitter. Caution should be used when cooking with untested cultivars; the flesh of some avocados may be rendered inedible by heat. Prolonged cooking induces this chemical reaction in all cultivars.
It is used as the base for the Mexican dip known as guacamole, as well as a spread on corn tortillas or toast, served with spices. Some people enjoy avocado with Marmite on toast.
In the Philippines, Brazil, Indonesia, Vietnam, and south India (especially the coastal Kerala and Karnataka region), avocados are frequently used for milkshakes and occasionally added to ice cream and other desserts. In Brazil, Vietnam, the Philippines and Indonesia, a dessert drink is made with sugar, milk or water, and pureed avocado. Chocolate syrup is sometimes added.
In Ethiopia, avocados are made into juice by mixing them with sugar and milk or water, usually served with Vimto and a slice of lemon. It is also very common to serve layered multiple fruit juices in a glass (locally called spreece) made of avocados, mangoes, bananas, guavas and papayas. Avocados are also used to make salads.
Avocados in savory dishes, often seen as exotic, are a relative novelty in Portuguese-speaking countries, such as Brazil, where the traditional preparation is mashed with sugar and lime, and eaten as a dessert or snack. This contrasts with Spanish speaking countries, such as Mexico or Argentina, where the opposite is true and sweet preparations are often unheard of.
In Australia and New Zealand, it is commonly served in sandwiches, on toast, or with chicken. In Ghana, it is often eaten alone in sliced bread as a sandwich. In Sri Lanka, well ripened flesh, thoroughly mashed with sugar, sugar and milk, or treacle (a syrup made from the nectar of a particular palm flower) was once a popular dessert.
In Mexico and Central America, avocados are served mixed with white rice, in soups, salads, or on the side of chicken and meat. In Peru, they are consumed with tequeños as mayonnaise, served as a side dish with parrillas, used in salads and sandwiches, or as a whole dish when filled with tuna, shrimp, or chicken. In Chile, it is used as a puree with chicken, hamburgers, and hot dogs; and in slices for celery or lettuce salads. The Chilean version of Caesar salad contains large slices of mature avocado. In Kenya, the avocado is often eaten as a fruit, and is eaten alone, or mixed with other fruits in a fruit salad, or as part of a vegetable salad. In Iran, it is used as a rejuvenating facial cream.
A puree of the fruit was used to thicken and flavor the liqueur Advocaat in its original recipe, made by the Dutch population of Suriname and Recife, with the name deriving from the same source.
Avocado slices are frequently added to hamburgers, tortas, hot dogs, and carne asada. Avocado can be combined with eggs (in scrambled eggs, tortillas or omelettes), and is a key ingredient in California rolls and other makizushi ("maki", or rolled sushi).
In southern Africa, Avocado Ritz is a common dish.
In the United Kingdom, the avocado became widely available in the 1960s when it was introduced by Marks and Spencer under the name 'avocado pear'. However, many customers tried to use it as a dessert ingredient like other pears (e.g. with custard), and complained to the store that it was inedible. As a result, Marks and Spencer dropped the word 'pear' and labelled it simply 'avocado'.
Avocados are high in valuable, health-promoting fats. For a typical avocado:
* About 75% of an avocado's calories come from fat, most of which is monounsaturated fat.
High avocado intake has been shown to have a beneficial effect on blood serum cholesterol levels. Specifically, after a seven-day diet rich in avocados, mild hypercholesterolemia patients showed a 17% decrease in total serum cholesterol levels. These subjects also showed a 22% decrease in both LDL (harmful cholesterol) and triglyceride levels and 11% increase in HDL (helpful cholesterol) levels. Additionally a Japanese team synthesised the four chiral components, and identified (2R, 4R)-16-heptadecene-1, 2, 4-triol as a natural antibacterial component.
As a houseplant
While not particularly popular, 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 container of water. In the latter method, the pit sprouts in four to six weeks, at which time it is planted in fertile soil such as potting soil. The plant generally grows large enough to be prunable; however, 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. To obtain fresh avocado produce, however, more than one tree must be cultivated for crosspollination.
Toxicity to animals
Avocado leaves, bark, skin, or pit are documented to be harmful to animals; cats, dogs, cattle, goats, rabbits, rats, birds, fish, and horses can be severely harmed or even killed when they consume them. The avocado fruit is poisonous to some birds, and the ASPCA lists it as toxic to many animals including cats, dogs, and horses. Avocado is an ingredient in AvoDerm dog food and cat food. However, the ASPCA has declined to say whether this food is safe or not.
Avocado leaves contain a toxic fatty acid derivative, persin, which in sufficient quantity can cause equine colic and, without veterinary treatment, death. The symptoms include gastrointestinal irritation, vomiting, diarrhea, respiratory distress, congestion, fluid accumulation around the tissues of the heart, and even death. Birds also seem to be particularly sensitive to this toxic compound. Feeding avocados or guacamole to any nonhuman animal should be avoided completely. Negative effects in humans seem to be primarily in allergic individuals.
The avocado may be an example of an 'evolutionary anachronism', a fruit adapted for ecological relationship with now-extinct large mammals (such as the giant ground sloth or the Gomphothere). 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 co-evolved 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. If so, the avocado occupies a similar ecological niche to the mango of Asia.
1. ^ Chen, H.; Morrell, P. L.; Ashworth, V. E. T. M.; De La Cruz, M.; Clegg, M. T. (2008). "Tracing the Geographic Origins of Major Avocado Cultivars". Journal of Heredity 100 (1): 56–65. doi:10.1093/jhered/esn068. PMID 18779226.
Source: Wikispecies: All text is available under the terms of the GNU Free Documentation License