| Farmer-based conservation of maize is important in Mexico, at least 3.5 million hectares under cultivation are planted to traditional varieties. The purpose of this study was to examine why maize landraces are maintained and replaced, and how are they changing in the Amecameca (2000 to 2500 masl) and Cuautla valleys (1200 to 1700 masl) of Mexico. A sample of maize types and a survey of seed management, production and income was accomplished in four communities. Communities studied had one to three major maize types which accounted for 85% or more of the maize area. Traditional varieties were found as major varieties in all communities. Several minor varieties were cultivated in all communities, rarely exceeding 5% of the maize area. At least one-half of the farmers plant only one variety, and all cultivate one of the major types. Major maize varieties within a community are competitive in yield and/or income to alternative types. Minor varieties are not in direct competition and are cultivated because of special characteristics and for trial purposes. Expected net income from maize production is low or negative, thus farmers seem to be maximizing utility and not profit. Opportunity costs for traditional varieties of maize seem to be with respect to other crops or salary work and not modern varieties. Traditional varieties have been replaced by both modern and other traditional varieties. Markets work both to conserve and replace traditional varieties. Each year a small proportion of farmers change seed of their traditional varieties, usually with seeds from within the community. Minor varieties are vulnerable because they are not essential for survival and few farmers cultivate them. Traditional varieties in the highland have smaller risk of replacement than in the lowlands. Evolution of maize is suggested by: the appearance of a new variety based on a historic type, attempts of hybridization among varieties, the disappearance of a previously known race, and introduction of two new major landraces. In three out of four communities major varieties have changed from those cultivated by the previous generation of farmers. Farmer and natural selection, broad genetic pools, and environmental and cultural heterogeneity promote the competitiveness of traditional varieties. |
