The avocado (Persea americana) is a tree native to Mexico, Central America, and Guam, classified in the flowering plant family Lauraceae. The name "avocado" also refers to the fruit of the tree with an egg-shaped pit. P. americana has a long history of being cultivated in Central and South America; a water jar shaped like an avocado, dating to A.D. 900, was discovered in the pre-Incan city of Chan Chan.The tree grows to 20 metres (65 ft), with alternately arranged leaves 12–25 centimetres long. The flowers are inconspicuous, greenish-yellow, 5–10 millimetres wide. The pear-shaped fruit is a true berry, from 7 to 20 centimetres long, weighs between 100 and 1000 grams, and has a large central seed, 5 - 6.4 centimeters long.
An average avocado tree produces about 120 avocados annually. Commercial orchards produce an average of 7 tonnes per hectare each year, with some orchards achieving 20 tonnes per hectare.[3] Biennial bearing can be a problem, with heavy crops in one year being followed by poor yields the next. The fruit is sometimes called an avocado pear or alligator pear, due to its shape and rough green skin. The avocado tree does not tolerate freezing temperatures, and can be grown only in subtropical or tropical climates.
The species is partially unable to self-pollinate, because of dichogamy in its flowering. The 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.
