2002. Farmers’ management of maize landrace diversity: A case study in Oaxaca and beyond

To assess the impact of farmer management on maize landrace diversity in the Central Valleys of Oaxaca, Mexico, where landraces comprise most of the maize grown, we interviewed farmers in six villages and collected and evaluated samples of seed. Among other things, we found that • the level of deleterious and lethal mutations is high in the landraces; • frequent seed and pollen exchanges, i.e., extensive migration and gene flow among landraces, result in a low differentiation between landraces; and • these same landraces show a strong differentiation for traits under selection by farmers (mainly ear traits). We also report on prior studies in Cuzalapa village, southwest Mexico and in Burkina Faso, which also examine the impact of migration and geneflow in open genetic systems. Because of high levels of recombination, most genes introduced from exotic varieties will behave independently and their diffusion is favored by seed and pollen exchanges. At the same time, these exchanges are components of the mechanisms that maintain and enhance the genetic diversity and viability of these landraces. Strategies that would restrict them will erode geneflow and result in genetic erosion