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Teosinte – maize’s wild ancestor

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Teosinte is a wild grass, which is closely related to maize. In fact, it is generally considered the ancestor of modern maize and has been recovered from cave sites in Oaxaca, Mexico occupied by humans as long as 4000 years ago.

teosinte

Figure 1. Teosinte growing in a maize field in Tlalco, Mexico.

Where is it found?

Teosinte grows in subtropical areas of Central America – regions of Mexico, Guatemala, and Nicaragua. Its distribution in Mexico and Guatemala parallels the ancient Mexican and Mayan civilizations, indicating that teosinte and maize have been in the same geographical area (sympatrically) for thousands of years. Teosinte growing in the Valley of Mexico was documented in Spanish writing four hundred years ago; they noted that teosinte is found in the same way that barley is found in wheat fields.
In terms of altitude, teosinte can be found up to about 2700 masl, though generally grows between 600 and 2000 masl, depending on the variety and the region.

How does teosinte compare with maize?

  • Teosinte and maize are unique among the grasses; in both, the male and female parts of the plant flower in different places.
  • Ears of teosinte are multi‐stalked, whereas ears of maize have only one stalk.
  • The maize plant puts its energy into producing only one ear; the teosinte plant will have multiple fruiting spikes.
  • The ears of teosinte will have only five to twelve kernels; ears of maize will contain five hundred or more kernels.
  • A single teosinte seed is enclosed in a fruitcase and the spike is two‐rowed. With maize, there are 8 to 22 rows on a massive cob and the spikelets are paired.
  • In teosinte the glume covers the seed, whereas in maize the seed is left exposed.
  • A tough casing called a rachis covers the teosinte kernels. This feature makes teosinte well‐adjusted to the agronomic system: teosinte is fed to the cows, it germinates in the manure pile, the manure pile is spread back onto the field, causing more teosinte to grow. Without this tough fruitcase, maize kernels are more accessible and are edible (digestible) for humans.
  • While modern maize requires human intervention in order to separate the grains from the cob for dispersal, teosinte naturally disarticulates. This means that it is possible for teosinte to grow wild.
  • The leaves of teosinte are narrower than those of maize.
  • The pests and diseases which attack maize are the same ones found on teosinte; however, their impact may differ. For example, the damage tolerance of teosinte to Lepidoptera is lower than that of maize.
  • Its growing season generally parallels that of maize: June through October in Mexico. Guatemalan teosinte has a slightly later growing season.

Teosinte and maize hybrids

The teosinte that can be found in farmer’s fields today is generally a hybridized form of teosinte. Teosinte found in Mexico is about 95% fertile with maize; Guatemalan teosinte is about 85% fertile with both maize and Mexican teosinte. This means that the Guatemalan teosinte has higher sterility and is likely an earlier form.

Hybrid clusters in fields can be attributed to a common parent that outcrossed in the previous year. An isolated teosinte plant surrounded by maize has a higher probability of outcrossing. If maize pollen and teosinte pollen reach the teosinte silks at the same time, often the teosinte will win.

multiStalked

Figure 2. Multi‐stalked ears of teosinte.

Why do farmers allow teosinte to remain in the field?

In some areas teosinte is considered a weed and farmers would like to exterminate it. However, in the early stages of growth teosinte plants are difficult to distinguish from maize. Farmers are usually hesitant to weed young plants, as the characteristics identifying plants as teosinte do not become apparent until fairly late in the growth stages. A farmer will not want to accidentally remove maize plants, so will let
plants remain in the field a little longer to be sure.

It is not until the tassel emergence that differences are clear – teosinte has a distinctive branching pattern that becomes apparent during this stage (Figure 1). By this time the teosinte has shed its pollen and hybridization has taken place.

Teosinte – more than just a weed

Another reason for teosinte to remain in the field is that farmers recognize its potential for other uses. It is being used as green forage for feeding to cattle. There are some farmers who have cows and are more interested in selling milk than they are in selling maize. Maize is sweet silage, but teosinte is also sweet silage, so to farmers more interested in dairy production the difference between the two is insignificant.
This means that there is a more relaxed approach to weeding the fields than there would be in areas more focused on maize production.

Future potential

Modern teosinte is still part of the story of maize: the extinction of any teosinte population would weaken our genetic knowledge of how modern corn came to be. It would be difficult to argue that teosinte does not have any practical uses, as it has more genes than maize. Whenever you can expand a genome, implications arise from the gene interaction. For instance, teosinte may one day be able to increase the production efficiency of starch or make a new kind of starch, as it has a harder starch than maize. As we don’t know what the food processing needs will be in the future, it is not possible to say that teosinte will not have a significant role in the future.

References:
Balter, M. 2007. Seeking Agriculture’s Ancient Roots. Science. 316(5833): 1830‐5.

Wilkes, H.G. 1997. Teosinte in Mexico: Personal Retrospective and Assessment. In J.A. Serratos,
M.C. Wilcox and F. Castillo‐González (eds.), Gene Flow Among Maize Landraces, Improved Maize
Varieties, and Teosinte: Implications for Transgenic Maize. Mexico, D.F.: CIMMYT. Pp. 10‐7.

Wilkes, H.G. 2007. Personal communication, 19 August.

Developed with input from J.Jones & P.Kosina • 2007