Journal of Ethnobiology 17(2) :249-266 Winter 1997 ETHNOMICROBIOLOGY: DO AGRICULTURAL PRACTICES MODIFY THE POPULATION STRUCTURE OF THE NITROGEN FIXING BACTERIA RHIZOBIUM ETLI BIOVAR PHASEOLI? VALERIA SOUZA, JENNIFER BAIN, CLAUDIA SILVA, VALERIE BOUCHET, ALDO VALERA, ERICKA MARQUEZ AND LUIS E. EGUIARTE. Departamento de Ecologia Evolutiva, Centro de Ecologia Universidad Nacional Aut6noma de Mexico AP 70-275, Covoacan 04510, Mexico D.F. Mexico ABSTRACT.-We analyze how agricultural practices affect the levels of genetic variation and the genetic structure of beans (Phaseolus vulgaris and P. coccineus) and of their associated bacteria Rhizobium etli. Two contrasting communities in the state of Puebla, central Mexico, were selected for this study : San Miguel, a Nahuatl community where traditional agricultural work is done almost exclusively by women, and Calpan, where men cultivate crops using modem techniques. The results are compared with previous research from Morelos, also in central Mexico. Wefound that San Miguel has maintained its agricultural tradition for generations. In recent years, women have played an important role not only in preserving this tradition but also in conserving the biological diversity in their plots. In Calpan, by contrast, the local varieties of beans have been replaced by commercial varieties and the women participate minimally in agriculture. In general terms, the genetic diversity of R. etli associated with cultivated beans (both P. vulgaris and P. coccineus) is high in all the communities we studied, while it is lower for the rhizobia associated with wild beans. The population structure of Rhizobium etIi is different in the two communities: the most fertile and intensively managed plots are similar in this respect, while the least managed plots resemble the site of wild P. vulgaris . This research indicates that agricultural practices and local environmental conditions affect the genetic structure of both cultivated beans and their associated bacteria. RESUMEN .-Analizamos c6mo las practicas agrfcolas afectan los niveles de variaci6n genetica y la estructura genetics de los frijoles (Phaseolus vulgaris y P. coccineus) y de sus bacterias asociadas, RhizobiumetIi, y el papel de las mujeres en la conservaci6n y manejo de esta diversidad genetica. Se seleccionaron dos comunidades contrastantes en el estado de Puebla, en el centro de Mexico: San Miguel, una comunidad nahuatl donde el trabajo agricola tradicionallo !levan a cabo casi exclusivamente mujeres, y Calpan, una comunidad mestiza donde los hombres cultivan el campo usando tecnicas modemas . Los resultados se comparan con investigaciones previas realizadas en Morelos, tarnbien en el centro de Mexico. Encontramos que San Miguel ha mantenido su tradici6n agricola por generaciones. En afios recientes, las mujeres han jugado un papel importante no s610preservando esta tradici6n sino conservando la diversidad biol6gica en sus parcelas. Sin embargo, en Calpan las variedades locales de frijol han sido substituidas por variedades comerciales y las mujeres estan perdiendo sus tradiciones y su contacto con la tierra. En terminos generales, la diversidad genetica de R. etli asociado a frijoles cultivados (tanto P. vulgaris como P. coccineus) es alta en todas las comunidades estudiadas,