Growth Characteristics of Landrace Maize Across an Elevation Gradient in Mexico.

The maintenance of crop yield depends on the continued performance of crop varieties to varying local environments. Southern Mexico, the crop center of origin for maize, features strong elevation gradients.  Climatically heterogeneous environments can be found within relatively small areas, creating an ideal study site for understanding local adaptation. Employing a reciprocal transplant common garden design, populations of open-pollinated maize from three elevation zones were collected and compared in 2011 and 2012 at common gardens located in elevation zones from where seed was sourced (600, 1550, and 2100 m). Farmer-saved seed remain responsive to selection by local environments, therefore some transplants demonstrate how populations are likely to respond to changing climate. The ability of landraces to adapt or respond plastically to new environments is likely to predict their continued use and conservation by farmers. Yet, a clearer understanding of the mechanisms that underlie local adaptation and plastic response is necessary. Physiological traits such as photosynthetic rate and stomatal conductance are important determinants of biomass accumulation and fitness. Sequential destructive harvests of aboveground biomass were collected, dried, and weighed in both years to calculate relative growth rates. In 2011, infrared gas analyses of sun leaves were conducted on plants shortly before flowering. Photosynthetic rate showed a GxE interaction where in both the highest and lowest common garden elevations, local types performed the best. Together, these physiological data can help clarify basic questions about local adaptation, which may prove useful for informing conservation in this region of globally important crop genetic resources.