What is teosinte?

Teosinte is the common name for a group of four annual and perennial species of the genus Zea native to Mexico and Central America (Doebley 1990; Sanchez et al. 1998; Wilkes 1967). Teosinte plants are taller and broader-leaved than most grasses (Figure). Their general growth form is similar to that of maize, although they have much longer lateral branches. The name, teosinte, is of Nahuátl Indian origin, and it has been interpreted to mean “grain of the gods”. Some species of teosinte are distinct from maize both genetically and taxonomically, and they appear not to have played any role in the origin of maize. However, one form of teosinte, known as Z. mays ssp. parviglumis, shares a particularly close genetic relationship with maize and available evidence indicates that it is the direct ancestor of maize (Doebley 1990; Matsuoka et al. 2002). This latter teosinte grows in the valleys of southwestern Mexico. In these regions, it grows commonly as a wild plant along streams and on hillsides, although it can also invade cultivated fields as a weed. It is most common in the Balsas River drainage of southwest Mexico and hence is also known as Balsas teosinte.

While the maize and teosinte plants share a similarly robust growth form, their female inflorescences or ears are strikingly different. The teosinte ear possesses only about 5 to 12 kernels, each sealed tightly in a stony casing (Figure). Collectively, the kernel and its stony casing are known as a fruitcase. At maturity, the teosinte ear disarticulates such that the individual fruitcases become the dispersal units. Protected within its casing, the teosinte kernel can survive the digestive tracks of birds and grazing mammals, enabling the seed to be easily dispersed (Wilkes 1967). By comparison, the massive maize ear can bear 500 or more kernels, each of which is attached to the central axis of the ear or cob. The kernels are naked without adequate protection from predation and are easily digested by any animal that consumes them. Since the kernels are firmly attached to the cob and the ear does not disarticulate, a maize ear left on the plant will eventually fall to ground with its full suite of kernels. When hundreds of maize kernels germinate the next season so close to one another, the emerging plants are unable to obtain adequate light and soil to grow and reproduce. Thus, maize is completely dependent on humans for its survival.

Doebley JF. 1990. Molecular evidence and the evolution of maize. Econ Bot 44 (3 supplement): 6-27.

Matsuoka Y, Vigouroux Y, Goodman MM, Sanchez J, Buckler ES, Doebley JF. 2002. A single domestication for maize shown by multilocus microsatellite genotyping. Proc Natl Acad Sci USA 99: 6080-4.

Sanchez J, Kato TA, Aguila RM, Hernandez JM, Lopez A, Ruiz JA. 1998. Distribución y caracterizacion del teocintle. Guadalajara, México: Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias.

Wilkes HG. 1967. Teosinte: The closest relative of maize. Cambridge, MA: The Bussey Institute, Harvard University.

When was maize domesticated?

The best estimate is that maize was domesticated between 6,000 and 10,000 years ago. First, the oldest archaeological maize dates to 6,000 years ago (Pipierno and Flannery 2001) so maize domestication must have occurred at this time or earlier. Second, the earliest time for the domestication of any crops in Mexico is 10,000 years (Smith 1997) ago so maize domestication is unlikely to preceed this date. Finally, molecular dating suggests that maize was domesticated about 9,000 years ago (Matsuoka et al. 2002), which is consistent with the archaeological evidence.

Matsuoka Y, Vigouroux Y, Goodman MM, Sanchez J, Buckler ES, Doebley JF. 2002. A single domestication for maize shown by multilocus microsatellite genotyping. Proc Natl Acad Sci USA 99: 6080-4.

Piperno DR, Flannery KV. 2001. The earliest archaeological maize (Zea mays L.) from highland Mexico: new accelerator mass spectrometry dates and their implications. Proc Natl Acad Sci USA 98: 2101-3.

Smith BD. 1997. The initial domestication of Cucurbita pepo in the Americas 10,000 years ago. Science 276: 932-934.

Where was maize domesticated?

Maize was likely domesticated in southern Mexico, perhaps either in the Balsas river drainage or the State of Oaxaca. The evidence for this statement comes from archaeological and genetic data. The oldest known archaeological maize was found in the State of Oaxaca in Southern Mexico (Pipierno and Flannery 2001), making this region a candidate for the location of maize domestication. A caution is that the archaeological record for the time period of maize domestication in Mexico is far from complete and thus even older maize may someday be found in other regions. Genetic data indicate that the type of teosinte most closely related to maize comes from the Balsas river drainage near where the States of Michoacan, Mexico and Guererro meet (Matsuoka et al. 2002). Thus, this region can also be considered a candidate for the location of maize domestication. A caution for this view is that the modern distribution of teosinte may differ from its distribution at the time of maize domestication.

Matsuoka Y, Vigouroux Y, Goodman MM, Sanchez J, Buckler ES, Doebley JF. 2002. A single domestication for maize shown by multilocus microsatellite genotyping. Proc Natl Acad Sci USA 99: 6080-4.

Piperno DR, Flannery KV. 2001. The earliest archaeological maize (Zea mays L.) from highland Mexico: new accelerator mass spectrometry dates and their implications. Proc Natl Acad Sci USA 98: 2101-3.