Cactus pears or prickly pears (Opuntia spp. Cactaceae) are omnipresent plants of the Mexican landscape and have great historical and ethnobotanical significance. Ripe fruits and tender cladodes (pads), have been collected from the wild since preColumbian times, and the mature cladodes are used as a forage for livestock. Opuntia originated in Central Mexico and some parts of the Caribbean region (Benson 1982; Russel and Felker 1987). Today cactus pear is a well recognized fruit crop in Mexico cultivated throughout the central semiarid highlands.
A vast array of species are still found in the wild, while backyards contain mostly cultivars selected by farmers. Production at commercial level started in the 1960s and is based on outstanding plants taken from rural households where they provide food for the family (Bravo 1978; Pimienta 1990; Barbera et al. 1992). Orchards used foundation material obtained from plants bearing large fruit size, high color, and good flavor. The clones were named based on specific fruit and plant traits. It is difficult to identify plants based only on vegetative traits and most farmers and scientists still use fruit characteristics for descriptive purposes.
Official figures report that Mexico has 42,000 ha of cactus pear (SARH 1994) distributed in the central highland (2000 m) semiarid temperate part of the country, all of them under rainfed conditions. Mean annual precipitation ranges from 400 to 700 mm with a bimodal pattern. Soils are shallow to medium in depth, poor in organic matter, and acidic to lightly alkaline.
Central Mexico has the widest variability of Opuntia species and botanical varieties. Almost every family orchard in this region grows a mixture of cactus, with one or several uses, from fruit production to hedging. In contrast, cultivated orchards use only a small number of clones.
The most productive area near Mexico city is known as Las Piramides, because it is located around the monuments (pyramids) erected by the ancient inhabitants of the Teotihuacan Valley. This area relies mostly in a single cultivar 'Reyna' or 'Alfajayucan' grown under intense management in commercial orchards. A different situation is observed in the north central area (Guanajuato, Zacatecas, and San Luis Potosi states) where it is common to observe mixed orchards of several commercial cultivars. Cactus pear grow wild in feral land and in semi-domesticated way in family plantings.
In any small grove it is possible to find a sample of cultivars as well as wild un-named materials, some of which could be readily included as commercial cultivars (Fig. 2). This allows for the availability of Opuntia products for an extended season. The reservoir for a formal breeding program is enormous and almost untapped.