The avocado (Persea americana) is a tree native to Central Mexico, 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 of the tree, which may be pear-shaped, egg-shaped or spherical.
Avocados are commercially valuable and are cultivated in tropical and Mediterranean climates throughout the world. They have a green-skinned, pear-shaped fleshy body 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.
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 Spanish aguacate which in turn comes from the Nahuatl word ahuácatl (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 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 derives from the Spanish form avocado, “advocate”, which was formed as a folk etymology that substituted (and obscured) the Nahuatl origins of the word. The earliest known written use in English is attested from 1697 as “Avogato Pear”, a term which was later corrupted as “alligator pear”. The “advocate”-form appears in several other Germanic languages, such as the German Advogato-Birne, the Swedish advokatpäron, the Danish advokat-pære and the Dutch advocaatpeer. It is known as “butter fruit” in parts of India. In China it is known as è lí (鳄梨, a direct translation of “alligator pear”) or huángyóu guǒ (黄油果, “butter fruit”).
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, 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, New Mexico, Texas, Florida, Hawai’i, Ecuador and Rwanda. Each region has different types of cultivars.
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 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 a few days 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. 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.
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
Avocado is usually treated with a special technique to assist its sprouting process
A young avocado sprout
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.
Growing indoorsUsually, 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.
Americana, avocado plant flowersMain article: List of avocado 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 CaliforniaThe 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 (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”, and both Fallbrook and Carpinteria, California, host annual avocado festivals.
Two Hass avocadosChoquette
A seedling from Miami, Florida on the property of Remi Choquette. Now a favored commercial cultivar in south Florida.
While dozens of cultivars are grown, the Hass avocado is today the most common. It produces fruit year-round and accounts for 80% of cultivated avocados in the world. All Hass avocado 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. Hass trees have medium-sized (150–250 g), ovate fruit with a black, pebbled skin. The flesh has a nutty, rich flavour with 19% oil. A hybrid Guatemalan type, it can withstand temperatures to −1°C (30°F).
Gwen is 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 (100-200g), 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 −1°C (30°F).
A seedling reportedly grown from a ‘Taft’ avocado planted in Miami, Florida on the property of George Cellon, 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. It is also very commonly used as a rootstock for nursery production. Hardy to −4°C (25°F)
First grown on the Pinkerton Ranch in Saticoy, California, in the early 1970s, Pinkerton is a seedling of Hass’ 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 −1°C (30°F) and bears consistently heavy crops. A hybrid Guatemalan type, it has excellent peeling characteristics.
Developed from a chance seedling found in 1948 by James S. Reed in California, Reed 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 −1°C (30°F). Tree size is about 5 by 4 meters.
Developed by a farmer, James Bacon, in 1954, Bacon has medium-sized fruit with smooth, green skin with yellow-green, light tasting flesh. When ripe, the skin remains green, but darkens slightly, and fruit yields to gentle pressure. It is cold-hardy down to −5°C (23°F).
Possibly a cross between Mexican and West Indian types, Brogden originated as a seedling grown in Winter Haven, Florida on the property of Tom W. Brogden. The variety was recognized for its cold-hardiness to −5°C (22°F) and became commercially propagated as nursery-stock for home growing. It is noted for its dark purple skin at maturity.
A Mexican/Guatemalan cross seedling of Fuerte, this cultivar originated in Israel, and was put into production there in 1947.
Mature trees tolerate four hours at −6°C (21°F). The fruit has a smooth, thin, green skin that does not peel easily. The flesh is very pale green.
A Mexican/Guatemalan cross originating in Puebla, the Fuerte earned its name, which means strong in Spanish, after it withstood a severe frost in California in 1913. Hardy to −3°C (26°F), it has medium-sized, pear-shaped fruit with a green, leathery, easy to peel skin. The creamy flesh of mild and rich flavour has 18% oil. The skin ripens green. Tree size is 6 by 4 meters.
A Guatemalan/West Indian cross that originated from a seedling grown in Homestead, Florida on the property of J.J.L. Phillips, it was patented in 1937 and became a major commercial cultivar due to its cold hardiness and production qualities. The fruit is large, averaging over 2 pounds in weight, has an elliptical shape, and green, glossy skin. Hardy to −3°C (26°F).
Predominantly Guatemalan, with some Mexican race genes, Sharwil was selected in 1951 by Sir Frank Sharpe at Redland Bay, southern Queensland, Australia. The name “Sharwil” is an amalgamation of Sharp and Wilson (J.C. Wilson being the first propagator). Scions were sent from Australia to Hawaii in 1966. A medium-sized fruit with rough green skin, it closely resembles the Fuerte, but is slightly more oval in shape. The fruit has greenish-yellow flesh with a rich, nutty flavor and high oil content (20–24%), and a small seed. The skin is green when ripe. It represents more than 57% of the commercial farming in Hawaii, and represents up to 20% of all avocados grown in New South Wales, Australia. It is a regular and moderate bearer with excellent quality fruit, but is sensitive to frost. Disease and pest resistance are superior to Fuerte.
Originated by R.L. Ruitt in Fallbrook in 1926, this Mexican variety is hardy to −4°C (25°F). The large, pear-shaped fruit has a shiny, thin, yellow-green skin that peels moderately easily. The flesh is pale green with fibers and has a light flavor.
Other cultivarsOther 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.