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Persea americana (Avocado)

[= Persea drymifolia, Persea gratissima]

Life > eukaryotes > Archaeoplastida > Chloroplastida > Charophyta > Streptophytina > Plantae (land plants) > Tracheophyta (vascular plants) > Euphyllophyta > Lignophyta (woody plants) > Spermatophyta (seed plants) > Angiospermae (flowering plants) > magnoliids > Order: Laurales > Family: Lauraceae > Genus: Persea

Persea americana (Avocado)
Persea americana (Avocado) Persea americana (Avocado)

Persea americana, Cape Town, South Africa. [photos H.G. Robertson, Iziko ]

Native to Central and South America and domesticated by 500 BC. The name 'Avocado' and comes from the Aztec name meaning 'testicle tree'.

 

 

Wild Persea americana have a wide yet disjunct distribution in Central and South America, ranging from eastern Mexico through Central America to the northern Andes. It is found on mountains in cloud forest and on the lower slopes in rain forest with well-drained soils. Wild fruit are 4-5 cm in diameter with a 2 cm diameter seed. The large seed is an adaptation for supplying young plants with enough food to enable them to survive in the dim forest understorey until they can grow into a gap from a fallen tree. Large seeds like this are common in other species of tropical forest trees.

Avocado seeds dating to 7000 BC have been found at a Mexican archaeological site, . Seed sizes are similar to wild varieties indicating that fruit were being harvested in the wild rather than from trees grown under selective cultivation. It is only in archaeological deposits dated to about 500 BC that the abundance and size of Avocado seeds increases, indicating cultivation of plants from seeds selected on the basis of fruit size. However, at another archaeological site in Mexico, small, wild-sized seeds have been found in deposits dating to as late as 700 AD, indicating that the practice of Avocado cultivation took time to spread to all communities.

The Avocado fruit is an important food in South America and is nutritious with high levels of mainly unsaturated oils, minerals, vitamins and reasonable levels of protein. The oil is evidently similar in composition to olive oil. The name 'Avocado' originates from the Aztec name ahuacacuauhitl meaning testicle tree! The Spanish shortened it to aguacate and the English then turned it into Avocado.The Avocado was evidently viewed by Indians and Spanish colonisers alike as having aphrodisiac properties which made it popular among many, but unpopular among Christian leaders.

Avocado flowers are crosspollinated which means that developing independent genetic lines is difficult. In fact, crosspollination is promoted in the flowers by the stigma of a flower being receptive to pollen prior to pollen being released from that same flower. Avocado trees produce thousands of flowers and only about one in 5000 sets fruit. Considering it originated from South American forests, the Avocado is remarkable in its ability to thrive under a broad range of environmental conditions. It needs water and no frost and prefers unleached, nonacid soils, sun, and dry air.

The Spanish introduced the Avocado to the West Indies and the Atlantic islands such as the Canaries. Avocado only started being grown in West Africa, Mauritius and India in the 1700's but it took a long time for them to be grown as a major crop, probably attributable to poor fruit quality.  With the problem of crosspollination, it was difficult at that time to produce an orchard of Avocado trees with consistently high quality fruit, except by cutting out the trees that were poor fruit producers. The breakthrough came with the development of budding and grafting techniques which enabled fruit growers to clone favourable plants. Only by 1910 did California fruit growers realise the potential of growing Avocado trees and it was through efforts to find favourable cultivars that the famous Fuerte clone was introduced to California from Mexico in 1911. The Fuerte has pear-shaped fruit with a smooth, green skin and was developed in Mexico from hybridisation between Mexican and Guatemalan varieties. The well known Hass variety which has an egg-shaped fruit with a thick, rough, black skin, was developed by Rudolph Has in California from Guatemalan stock. At one stage there were hundreds of different varieties available but these eventually were wittled down to a few which include the Fuerte and the Hass.

Publications

  • de Villiers, E.A. 2001. Cultivation of avocado. ARC-Institute for Tropical and Subtropical Crops, South Africa, 368 pp. More details from ARC web site

  • Sauer, J.D. 1993. Historical geography of crop plants - a select roster. CRC Press, Boca Raton, Florida.

Text by Hamish G. Robertson 


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