Genetic Composition and Spatial Distribution of Farmer-managed Phaseolus Bean Plantings: An Example from a Village in Oaxaca, Mexico

摘要

In situ conservation of crop genetic resources is an important complement to ex situ conservation, yet little is known about how small-scale farmers perceive diversity in their own fields. In this study, we investigated the role of farmers from a community in the Sierra Juarez, Oaxaca, Mexico, in managing Phaseolus bean diversity in their fields. We collected seeds from 287 plants in 10 fields in the village of Santa Mar a Jaltianguis and evaluated the diversity present in the collection at 10 nuclear and three chloroplast DNA (cpDNA) microsatellite markers. Following a STRUCTURE analysis, three core population clusters were identified in the collection, a finding corroborated by morphological observations, principal coordinate analysis, and neighbor-joining tree construction using molecular data. The first two populations were identified as Phaseolus vulgaris L. ecogeographic races Mesoamerica and Jalisco and the third population as related species Phaseolus coccineus L. and Phaseolus dumosus Macfad. Each of the fields sampled consisted predominantly of a single Phaseolus species or ecogeographic race, but there was also evidence of low levels of gene flow between races Jalisco and Mesoamerica. Our data suggest farmers in Santa Mar a Jaltianguis recognize existing inter-and intraspecies diversity in Phaseolus, its differential adaptation, its capacity to exploit a broad range of growing environments, and its potential to buffer the community against sockioeconomic and climatic changes.