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Population structure and strong divergent selection shape phenotypic diversification in maize landraces

G Pressoir, J Berthaud, 2003

To conserve the long-term selection potential of maize, it is

necessary to investigate past and present evolutionary

processes that have shaped quantitative trait variation.

Understanding the dynamics of quantitative trait evolution

is crucial to future crop breeding. We characterized population

differentiation of maize landraces from the State of

Oaxaca, Mexico for quantitative traits and molecular markers.

Qst values were much higher than Fst values obtained

for molecular markers. While low values of Fst (0.011 withinvillage

and 0.003 among-villages) suggest that considerable

gene flow occurred among the studied populations, high

levels of population differentiation for quantitative traits were

observed (ie an among-village Qst value of 0.535 for kernel

weight). Our results suggest that although quantitative traits

appear to be under strong divergent selection, a considerable

amount of gene flow occurs among populations.

Furthermore, we characterized nonproportional changes in

the G matrix structure both within and among villages that

are consequences of farmer selection. As a consequence of

these differences in the G matrix structure, the response to

multivariate selection will be different from one population to

another. Large changes in the G matrix structure could

indicate that farmers select for genes of major and pleiotropic

effect. Farmers’ decision and selection strategies have a

great impact on phenotypic diversification in maize landraces.

Références complètes

G Pressoir and J Berthaud;International Maize and Wheat Improvement Center (CIMMYT), Mexico, DF, Mexico;2Institut de Recherche pour le De’veloppement (IRD), Montpellier, France;Heredity (2003), 1–7, www.nature.com/hdy

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