Domestication is a human-induced evolutionary process that results in rapid genetic changes in plant species. It is well documented that cultivated plants in advanced stages of domestication have undergone a progressive narrowing of their genetic base. However, the nature of genetic variation during the earlier stages of domestication (in cultivated populations that have yet to undergo the intensive selection of modern agriculture) is not well understood. This study uses DNA sequence data to explore genetic variation in a tropical fruit tree, Spondias purpurea L. (Anacardiaceae), a crop that is believed to be in the early stages of domestication. Spondias purpurea (jocote) is a native species of the dry forests of Mexico and Central America; it is cultivated from Central Mexico to northern South America and throughout the Caribbean. Jocotes are grown for their plum-like fruits, which are eaten fresh and made into jams and beverages. Cultivated jocote populations may have retained much of their genetic variation because of the way in which they were domesticated: most plants are found in isolated backyard trees, multi-crop farms, or living fences, with little production from well-ordered plantations. Selection on a highly local scale has resulted in great variation in fruit size, shape, color, and taste. We apply a phylogeographic approach to examine the geographic structure of genetic variation jocote populations. Sequences of the fourth intron of the nuclear-encoded phosphoenolpyruvate carboxylase gene (ppc) were obtained from a geographically diverse sample of S. purpurea. The amount of genetic variation at this locus was quantified for wild, non-cultivated populations and for different modes of cultivation: living fences, backyard trees/small farms, and orchards. A haplotype network was constructed and was used to infer historical relationships among jocote populations. Preliminary data suggest that high levels of genetic variation may have been maintained in cultivated jocote populations.

Key words: Anacardiaceae, crop origin, domestication, phylogeography, Spondias purpurea