Origin of maize: The tripartite hypothesis

Summary

The oldest known archaeological race of maize is a pod-popcorn. The closest living wild relative of cultivated maize is teosinte. Although the morphological differences between maize and teosinte are spectacular in appearance they are conspecific genetically. The tripartite hypotheses proposes that the ancestor of domesticated maize was a now extinct wild pod-popcorn; that teosinte originated from maize-Tripsacum hybridization; and that introgression with either teosinte or Tripsacum gave rise to the tripsacoid syndrome characteristic of many modern races of maize. Maize and teosinte cross readily, and exchange genes wherever they are sympatric. Hybrids between maize and Tripsacum are not always easy to produce, but natural introgression between these taxa is possible. However, artificially induced introgression from Tripsacum into maize failed to produce either teosinte-like offspring or the combination of tripsacoid characteristics assumed to indicate such introgression during the evolution of several South American races of maize. The available archaeological data seem to exclude teosinte as a possible ancestor of domesticated maize. This will make maize the only cereal without a living direct ancestor. Biosystematic studies suggest that teosinte is so closely related to domesticated maize that it could be accepted as the progenitor of maize.