After wild teosinte grass was first domesticated in southern Mexico, maize, commonly called corn, took both a high road and a coastal low road as it moved into what is now the U.S. Southwest, reports an international research team which did DNA analysis of corn cobs dating back over 4,000 years and provides the most comprehensive tracking to date of the origin and evolution of maize in the Southwest and settles a long debate over whether maize moved via an upland or coastal route into the U.S.
The study compared DNA from archaeological samples from the U.S. Southwest to that from traditional maize varieties in Mexico, looking for genetic similarities that would reveal its geographic origin.
"When considered together, the results suggest that the maize of the U.S. Southwest had a complex origin, first entering the U.S. via a highland route about 4,100 years ago and later via a lowland coastal route about 2,000 years ago," said co-author Jeffrey Ross-Ibarra, an associate professor in the Department of Plant Sciences at UC Davis.
The study further provided clues to how and when maize adapted to a number of novel pressures, ranging from the extreme aridity of the Southwest climate to different dietary preferences of the local people.
Excavations of multiple stratigraphic layers of Tularosa cave in New Mexico allowed researchers to compare genetic data from samples from different time periods.
"These unique data allowed us to follow the changes occurring in individual genes through time," said lead author Rute Fonseca of the University of Copenhagen. Researchers used these data to identify genes showing evidence of adaptation to drought and genes responsible for changes in starch and sugar composition leading to the development of sweet corn, desired for cultivation by indigenous people and later Europeans.
The study findings also show how climatic and cultural impacts influenced the genetic makeup of maize.
Published in Nature Plants. The international team of authors also included Bruce D. Smith of the National Museum of Natural History at the Smithsonian Institution and M. Thomas P. Gilbert, University of Copenhagen. The study was funded primarily by the Danish Council for Independent Research and a Marie Sk?owdowska-Curie fellowship from the European Commission.