Teosinte, as the wild progenitor of maize, was adapted for survival under the stress of high population density. The competition for space and sunshine came from other teosinte plants as well as other species of wild plants. The survival of teosinte required adaptation to population stress.
During domestication, the developing maize changed its adaptation to low density conditions resulting from slash and burn clearing of land before planting and weed removal afterwards. In a few cases (Oloton), the competition for sunshine was won by evolving giant stalks that would tower up over small trees and shrubs. Water was necessary sometimes from irrigation or near seepage areas at the base of mesas in the desert. When intercropping maize with other food plants such as beans and squash, the maize was spread out in space or time so that there was no competition between canopies for sunshine. In the several hundreds of races of maize, including modern varieties of sweet corn, in almost every case the adaptation is to low density conditions.
During the last ten or more years, plant breeding for adaptation to crowding resulting from new technologies for high density planting simulates a return to the wild, high-density conditions of 8,000 years ago. The adaption now comes from smaller erect leaves, and slightly reduced plants and ears together with greatly reduced tassels. This is the new industrial maize of high density monoculture that is flooding the world market with enormous yields of cheap feed corn.
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