Ecogeography and Taxonomy of Teosinte.

Teosinte, the closest relative of maize, is represented by annual and perennial diploid (2n=20) and tetraploid species (2n = 40). They have been reported within the tropical and subtropical areas of Mexico, Guatemala, Honduras, and Nicaragua as isolated populations of variable dimensions occupying from less than one acre to several square kilometers. Teosinte grows in a variety of ecological conditions from hot and humid regions to cool and dry valleys in Northern and Central Mexico. Annual mean temperature ranges from 13 to 29 ^oC and the gradient in annual rainfall in its distributional range is wide (450-3500 mm). Teosinte can be found on the edge and within maize fields, on the edge of small streams, in open woods on rocky slopes of mountains and as a constituent of the herbaceous cover in grassy areas. The distribution of teosinte extends from the southern part of the cultural region known as Arid America, in the Western Sierra Madre of the State of Chihuahua, to the western part of Nicaragua. A point worth highlighting is that populations do not have a uniform distribution; rather there are specific climate, soil, and human circumstances under which they can be found. The annual form of teosinte received the scientific name of Euchlaena mexicana Schrader, in 1832; later during the early decades of the 20th century all annual forms of teosinte were included within Zea mexicana (Schrader) Kuntze. Based on a detailed ecogeographical characterization, cytological and morphological data, Wilkes described six races of teosinte from México and Guatemala in 1967. Based on the studies of Doebley and Iltis during the 1980’s, the genus Zea contains eight taxa divided into two sections (Zea and Luxuriantes) and five species. Recently, three new taxa from Mexico were reported within section Luxuriantes from Nayarit, Michoacan and Oaxaca. As in many Latin American countries, the introduction of modern crop varieties and the replacement of local landraces and their wild relatives have contributed to the erosion of genetic diversity. There is only one project for in situ conservation in Mexico, however, as a result of several collection missions during the last 30 years, three major teosinte collections are conserved in germplasm banks at Instituto Nacional de Investigaciones Forestales Agricolas y Pecuarias, Univeridad de Guadalajara, and International Maize and Wheat Inprovement Center.