G Pressoir, J Berthaud,
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.
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