There's been a couple of cool articles in Scientific American about the great diversity of corn grown by family farmers in Mexico. These hyper-local varieties maintain a large genetic diversity that could help corn adapt in the future. A case in point is the second article here, which describes a strain grown in Oaxaca that fixes most of its own nitrogen. Nitrogen dependence is corn's Achilles heel, and the main reason that we need to fertilize it. The author even speculates that we may have accidentally bred out corn's ability to fix nitrogen a long time ago, and that perhaps we could bring it back on a larger scale.