Persea americana (Avocado)
[= Persea drymifolia, Persea
gratissima] Life
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> Tracheophyta (vascular plants) > Euphyllophyta > Lignophyta (woody plants)
> Spermatophyta (seed plants) > Angiospermae (flowering
plants) > magnoliids > Order: Laurales > Family: Lauraceae
> Genus: Persea
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
-
Sauer, J.D. 1993. Historical geography of
crop plants - a select roster. CRC Press, Boca Raton, Florida.
Text by Hamish G. Robertson |