The Origin of Maize

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Abstract
There have been 3 general theories regarding the origin of maize: (1) that it originated from podcorn, Zea mays tunicata, which differs from normal maize primarily by a single dominant gene governing the development of a brittle, disarticulating rachis and the production of prominent glumes enclosing the seeds; (2) that maize originated from teosinte, Euchlaena mexicana, by direct selection, by large scale mutations or by the hybridization of Euchlaena with a grass now unknown; (3) that Zea, Euchlaena and Tripsacum, the 3 American Maydeae have descended along divergent and independent lines from a remote common ancestor. New evidence from cytogenetic studies at the Texas Expt. Station suggest that Euchlaena has had no part in the ancestry of maize, but is instead the product of natural hybridization of Zea and Tripsacum. Euchlaena which is intermediate between Zea and Tripsacum in many characteristics differs genetically from Zea primarily by 4 segments of chromatin, all of which have genes with Tripsacum effects. Hybrids of Zea and Tripsacum have shown that there is some association between chromosomes of the 2 genera and that interchanges of chromatin may occur. The combined data agree in pointing to the comparatively recent origin of Euchlaena as the result of natural hybridization of Zea and Tripsacum. With Euchlaena eliminated from a role in the origin of maize, it is reasonable to assume that maize originated as a mutation from a wild pod-corn once indigenous, and perhaps still to be found, in the lowlands of S. America. The primary center of domestication probably occurred in the Andean region of Peru and Bolivia. Historical and archaeological evidence supports this view. The hybridization of Zea and Tripsacum which occurred when the 2 genera were brought into contact with each other in Central America gave rise not only to the new genus Euchlaena, but to new forms of maize which spread in both directions, almost completely replacing pure maize in all regions except the Andean. Cytological evidence on chromosomal knobs supports the view that almost all modern maize vars. are contaminated with Tripsacum.

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