**2. Regional maize genetic diversity**

In any crop system, the genetic diversity is determined—among other factors—by the use of diverse types of local varieties. Conceptually, two types of genetic materials are commonly developed, those obtained from preferences (color, flavors, crop type, etc.) and those selected for adaptability to biotic or abiotic micro-environments [4]. In addition to the native population for a particular environment, maize genetic diversity is associate to other factors that may change the genetic structure in a population such as the seed exchange among farmers within a community or among different communities, and, depending on the migration index and introgression of foreign germplasm, would contribute to the genetic variation in a native population [5, 6].

The maize (*Z. mays* L.) is a native crop of Mexico, and it is the place where the highest genetic diversity is found. This crop is adapted to the most diverse environmental conditions; thus, the specific local adapted populations (landrace) have been developed, with particular attributes that differentiate each other, within and among regions, circumstances that make possible to recognize Mexico as center of origin and diversification [7]. Commonly, the maize diversity has been described by the racial classification approach, which allowed to identify the first 25 races of maize in Mexico, based on morphological data (plant, ear, and tassel) [8].

In the region of study, the maize diversity has been documented by the presence of representative race populations in Coahuila state, such as Tuxpeño [8], Raton and Tuxpeño Norteño [9], Celaya, Conico Norteño, Elotes Conicos, and Olotillo [10]. A case study carried out in native populations from Coahuila State in Mexico, indicated that genetic diversity shows a continuous pattern among racial complexes, and is associated to the altitudinal and ecological regions [11].
