The different patterns of chromosome knobs and other diverse traits of maize have led McClintock, Randolph and Kato to independently suggest that modern maize stems from multiple domestications of its wild ancestor.
New evidence supporting at least two independent domestications from two different teosintes comes from the comparative morphology of the cobs and kernels of two ancient indigenous races of maize from Mexico. It appears that the emergence of the maize kernel from the cupulate fruit case of teosinte about 8,000 years ago was accomplished by two different systems during two or more independent domestications. Understanding these systems has a bearing on corn improvement. In the Nal Tel-Chapalote system, the kernel emerged by an elongation of the rachilla within the female spikelet. In the Palomero Toluqueno system, emergence was by way of an elongation of the kernel while its rachilla remained short. The present descendants with cobs based on rachilla elongation are most common in U.S. corn, especially in the Northern Flints. The second system, by kernel elongation, has among its descendants the Gourd Seed - Shoe Peg types and, to a lesser extent, the Southern Dents in general.
The Corn Belt Dent is known from historical records to be a hybrid between the Southern Dents and Northern Flints. Much of its heterosis appears to stem from combining these diverse parents. Further back, the source of the heterosis may stem in part from either early isolates of domesticated teosinte or from independent domestications of two different teosintes.
It is suggested that the Nal Tel-Chapalote system came from domesticated Guerrero teosinte while the Palomero Toluqueno system came from Chalco teosinte.
Walton C. Galinat
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