DNA from primitive maize landraces and archaeological remains: implications for the domestication of maize and its expansion into South America

To study the origins of South American maize, without the complicating factors introduced by the extensive movement of genotypes during the post-Columbian period, we made a genetic analysis of primitive landraces and preserved maize remains. Fifteen alcohol dehydrogenase 2 (Adh2) allele sequences were obtained from the landraces and 11 from the archaeological specimens. When these and six previously published Adh2 sequences were aligned, three allele groups were seen, distinguished by the structure of a dinucleotide repeat sequence. The three allele groups had distinct distributions within South America, the distributions supporting a model in which the two Central American agricultural systems-highland and lowland-generated separate expansions of maize cultivation into South America. One expansion centred on a highland culture that spread from Central America through the Panama highlands into the Andean regions on the western side of South America, and the second expansion centred on a lowland culture which spread along the lowlands of the northeast coast of South America, entering the continent through the river systems. The Adh2 biogeography was consistent with limited cultural contact across the Andes between northern Chile and Paraguay. From the diversity of the Adh2 allele sequences, we deduced that maize has undergone a rapid rate of evolution since domestication. (C) 2003 Elsevier Science Ltd. All rights reserved.