Landrace conservation of maize in Mexico: an evolutionary breeding interpretation

Periodo de realización: 1900/01/01 al 2016/01/01

Tipo: Capítulo de libro

Lugar(es) de estudio: México
Resumen: "In situ conservation has been the minor partner in crop conservation efforts, ex situ methods have been the preferred option. It is presently considered that both approaches should be viewed as complementary, yet ex situ procedures have shaped the views for on-farm conservation. On-farm conservation is for household livelihoods, genes for breeders should be viewed as a byproduct. A review of the Mexican case for maize is presented. De facto on-farm conservation of maize landraces in Mexico is widespread and vigorous with more than 2 million farmers sowing landraces in more than half of the 8 M ha that are planted annually. For most small-scale farmers maize represents food security more than a business and at present maize is no longer the main income for most of these households. Several major factors describe the presence of maize landraces in the Mexican landscape. A highland-lowland axis is prominent, where the highlands are completely dominated by landraces and in the lowlands there is a strong adoption of commercial cultivars with varying presence of landraces. There is a north-south axis with much greater prevalence of commercial cultivars in the high quality irrigated lands of the north, and landraces are ubiquitous in the steep rainfed landscapes of the south. Genetic variation has been found to be largest within landraces (or races) more than between them, though there are private alleles and significant homozygote excess related to morphologic or phenologic differences. Although traditional seed systems are very local and experimentation with new varieties is a main motive for acquiring seed, the effect of artificial selection by farmers has not been well described. Particular qualities of the grain may be important to maintain demand for some maize races, but main use is generic (tortilla) and quality does not seem to affect the demand for most varieties. Based on race richness, western and central Mexico has the greatest diversity and richness has not decrease significantly in the last 60 years. Maize landraces are not static and some are changing to respond to markets and possibly other factors. An evolutionary breeding interpretation, within a subsistence food security focus, of Mexico’s maize case is proposed, where natural selection of landraces with broad genetic bases is producing the seed indispensable for millions of farmers."

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