The Origin, Nature, and Genetic Improvement of the Avocado

Abstract

Discussion of avocado botany, including the three horticultural races. Three root characteristics and their consequences. Race differences in root traits. The avocado's historical importance. Its world spread. Present world distribution with relative rankings. The unique avocado flower behavior. Breeding methods: self-pollination, cross-pollination, pollinators, pollination methods, artificial mutation, spontaneous mutation (and budwood cutting). Breeding results. The 'Gwen'. New selections. Biotechnology. Propagation and tree structure. Origin and Botany The avocado (Persea americana Mill.) is in the Lauraceae family. The Persea species are classified into two subgenera, Eriodaphne and Persea. Eriodaphne contains most of the hundred or so probable species, including a few with iron-clad resistance to the great world-wide avocado scourge: root rot caused by Phytophthora cinnamomi. Subgenus Persea contains the commercial avocados, in genus Persea, species americana. Unfortunately, the two subgenera have so far proven totally incompatible; we can only hope that future biotechnology will enable us to bridge this chasm and so benefit the avocado with Eriodaphne genes. The exact number of genus Persea species is unknown. There have been reports of Perseas, or closely related species, in the Japan-Taiwan-southern China region. There is even a rumor that a form from there, tentatively described as genus Machimus, is actually graft-compatible with P. americana, and may even have rootstock advantage. The whole matter needs early, thorough investigation.