Differentiation and genetic diversity of Phaseolus lunatus wild populations from Chiapas, Mexico, and their genetic relationships with MI and MII groups

Background: Understanding the genetic structure of wild relatives of domesticated species is crucial for its conservation and to elucidate the sites of crop domestication. Lima bean is one of the five domesticated Plzaseolus species and Mexico is one of its centers of domestication. Recent studies showed the existence of two wild gene pools (MI and MII) of this species in Mexico and suggested that their genetic divergence occurred in southeast Mexico. Question: Did MI and MII groups diverged around the Isthmus of Tehuantepec, Mexico? Studied species: Lima bean: Neotropical plant species, herbaceous, with an annual/short life cycle and with autogamous tendency. Study site and years of study: Seven wild populations were collected in 2012 in the State of Chiapas, Mexico, area underrepresented in previous studies. Methods: Genetic diversity and grouping patterns of collected populations and their relationship to MI and MII groups were analyzed at eight microsatellite loci. Results: High genetic structure (F-ST: 0.42 to 0.96) and a high level of genetic diversity (H-E = 0.48) were found. The analyses, and presence of admixed populations in MI and MII, suggested that the genetic divergence of these groups is an ongoing process centered around the Isthmus of Tehuantepec. Conclusions: Our results support the hypothesis that MI and MII groups diverged around the Isthmus of Tehuantepec; however, sampling should be increased both at population and genomic levels, to determine the precise organization of the genetic diversity of wild P. lunatus from Mexico.