Local Adaptation and Adaptive Genetic Structure in Maize Landraces in Mexico.

Landraces or traditional varieties of crops can be locally adapted to the specific, diverse environments from which they come, especially in centers of crop diversity.  However, studies of local adaptation per se are rare for crop genetic resources and we know little about the degree to which populations from similar environments differ in their adaptive characteristics.  We studied the patterns of local adaptation of 32 landraces and locally-available commercial varieties of maize in Chiapas, Mexico and explored how adaptive genetic variation was structured within and among elevations at which landraces were collected.  To do so, we used data from common gardens performed at three elevations along the same transect from which landraces were sourced.  We saw clear patterns of local adaptation, although not all measures of fitness or experimental years yielded the same patterns.  For instance, total weight of seed produced per emerged seedling and anthesis-silking interval showed local adaptation more clearly than survival to reproduction and total number of seed produced per emerged seedling.  An extremely challenging, droughty year reduced our ability to discern local adaptation of the mid-elevation collections in 2012.  We also found that variation among maize collected from different communities within each elevation or from different farmers within each community was greater for flowering time than for fitness traits, indicating differential selection for these traits.  This work contributes to the needed regional evaluation of adaptive diversity of maize under ecological conditions relevant to assessing responses to climate change.