The Putative Mesoamerican Domestication Center of Phaseolus vulgaris Is Located in the Lerma-Santiago Basin of Mexico

Mesoamerican food agriculture is defined by the milpa cropping system, consisting of maize (Zea mays L.), common bean (Phaseolus vulgaris L.), and squash (Cucurbita spp.). In recent years, a domestication center for maize has been proposed in the Balsas River basin in west-central Mexico, raising the question whether the Balsas basin was also the center of origin for Mesoamerican food agriculture in general. We conducted a survey of genetic diversity for 26 microsatellite markers in a representative sample of 155 wild and domesticated common bean from its Mesoamerican gene pool. Microsatellite diversity was analyzed with STRUCTURE, neighbor-joining tree construction, and principal coordinate analysis. Most Mesoamerican domesticated accessions clustered in a single group, suggesting a single domestication. Furthermore, the most closely related wild beans to the domesticated clade originated from a restricted region in the Rio Lerma-Rio Grande de Santiago basin in west-central Mexico, distinct from the Balsas basin. Although wild maize and Phaseolus beans grow together in the wild, they appear to have been domesticated in different regions to be reunited later on in a single cropping system. Crop domestications in Mesoamerica may therefore have a diffuse rather than a single geographic origin. Archaeological and ecological investigations into the origins of agriculture should be refocused from the arid eastern half of Mexico to the west-central part of the country.