Zea (genus) - Origin of Maize and Interaction With Teosintes

Origin of Maize and Interaction With Teosintes

Teosintes are critical components of maize evolution, but opinions vary about which taxa were involved. According to the most widely-held evolutionary model, the crop was derived directly from Z. m. parviglumis by selection of key mutations; up to 12% of its genetic material came from Z. m. mexicana through introgression. Another model proposes that a tiny-eared wild maize was domesticated, and after being spread from east-central Mexico, this cultigen hybridized with Z. luxurians or Z. diploperennis resulting in a great explosion of maize genetic diversity, ear and kernel forms, and capacity to adapt to new habitats, as well as increased yields. A third model suggests that the early maize resulted from a cross between Z. diploperennis and a species of Tripsacum; support for this is minimal. A fourth model posits that teosinte resulted from hybridization between an early wild form of Z. m. mays and Tripsacum.

All but the Nicaraguan species of teosinte may grow in or very near corn fields, providing opportunities for introgression between teosinte and maize. First- and later-generation hybrids are often found in the fields, but the rate of gene exchange is quite low. Some populations of Z. m. mexicana display Vavilovian mimicry within cultivated maize fields, having evolved a maize-like form as a result of the farmers' selective weeding pressure. In some areas of Mexico, teosintes are regarded by maize farmers as a noxious weed, while in a few areas farmers regard it as a beneficial companion plant, and encourage its introgression into their maize.