Genetic diversity and maize seed management in a traditional Mexican community: implications for in situ conservation of maize

Abstract

Results from a study of maize varieties and seed sources in a traditional community in Mexico raise questions about the relevance of models for in situ conservation of crop genetic resources that are based on geographical isolation of the community, as well as the relationship between genetic erosion and the introduction of varieties. The morphophenological diversity of local materials is shown to be enhanced by introductions of both improved cultivars and landraces from farmers in other communities. Evidence on seed sources and selection practices also reveals that the geographical point of reference for defining a "local" landrace is larger than the community itself. Farmers often obtain seed for their landraces from other farmers in and outside the community, rather than select seed exclusively from their own harvests. A farmer will classify seed obtained from another community as that of a local landrace if it resembles one of his own, according to the phenotypic characteristics that he uses to distinguish varieties. A more appropriate model for conserving maize diversity in this community would be to permit a certain level of introductions while assuring that the extent of cultivation of local varieties is sufficient to maintain a desirable level of polymorphism. The design of such an in situ system would clearly be much more complex than the simple model based on geographical isolation would suggest.