Teosinte refers to a group of wild grasses belonging to the genus Zea, primarily found in Mexico and Central America. These plants grow in various habitats, including moist areas along streams and hillsides, and sometimes in disturbed ground or bordering agricultural fields. Teosinte includes several species such as Zea diploperennis, Z. luxurians, Z. nicaraguensis, and Z. perennis, along with three subspecies of Zea mays: Z. mays subsp. huehuetenangensis, Z. mays subsp. mexicana, and Z. mays subsp. parviglumis.
Ancestor of Corn
Teosinte is identified by genetic and archaeological findings as the direct wild ancestor of modern cultivated maize, commonly known as corn. Domestication began approximately 9,000 years ago in the Balsas River region of Guerrero and Michoacán, Mexico. Among teosinte species, Balsas teosinte (Zea mays subspecies parviglumis) shares the closest genetic relationship with domesticated maize (Zea mays subspecies mays), making it the primary progenitor.
This understanding is largely based on the genetic similarity between modern maize and Balsas teosinte. Early research by George W. Beadle in the 1930s showed that maize and teosinte have very similar chromosomes and produce fertile hybrids, suggesting they are the same species. Later, DNA profiling confirmed Balsas teosinte from the Central Balsas River Valley as the genetic origin of all maize varieties. Archaeological discoveries of ancient maize cobs in regions like Tehuacán, Mexico, further support this link, showing a gradual transformation from teosinte-like structures to modern corn characteristics over thousands of years.
Distinguishing Features
Teosinte plants differ significantly from modern corn. A typical teosinte plant is a tall, branching grass, producing multiple long lateral branches, each tipped with a tassel, which is the male inflorescence. This contrasts with modern corn, which has a single, stout stem and one or two short lateral branches, each bearing an ear.
Teosinte ears also differ from corn. They are small, measuring about 2-3 inches, with only one row of triangular-shaped seeds. Each kernel is encased in a tough, stony fruitcase or glume, making the dry grain largely inedible without extensive processing. In contrast, modern corn has much larger ears with numerous exposed kernels arranged in multiple rows. Teosinte seeds naturally shatter or disperse from the plant when ripe, a mechanism that aids wild propagation but is absent in domesticated corn, which retains its kernels on the cob.
Domestication Journey
The transformation of teosinte into maize was a domestication journey spanning thousands of years, driven by early human selection. This process involved significant changes in plant architecture and ear morphology. A genetic alteration occurred in the teosinte glume architecture 1 (tga1) gene. A single mutation in this gene, a change in one nucleotide, led to the reduction of the tough fruitcase surrounding the kernels, making them more accessible and edible.
Another genetic change involved the teosinte branched 1 (tb1) gene, which controls stem branching. The expression of the tb1 gene shifted teosinte’s highly branched growth form to the single-stalked structure characteristic of maize, with ears developing laterally on shorter branches. Archaeological evidence suggests the tb1 allele found in modern maize was established around 5,000 years ago. These genetic modifications, along with human selection for traits like larger ears, increased kernel numbers, and non-shattering ears, gradually reshaped teosinte into the corn we recognize today.
Modern Relevance
Teosinte remains important in agricultural science and research. As the wild ancestor of modern maize, it represents a reservoir of genetic diversity, including alleles that may have been lost during domestication. This genetic diversity makes teosinte a valuable resource for improving modern corn varieties. Researchers explore teosinte for traits such as disease resistance, drought tolerance, and enhanced nutritional quality.
For instance, the UPA2 allele from teosinte has been shown to increase maize yield under high-density planting conditions by modifying the plant’s architecture. Teosinte’s genetic makeup also includes alleles that influence kernel composition, such as starch, protein, and oil content, which could improve the nutritional value of maize. Modern genetic analysis techniques facilitate the transfer of these beneficial traits into cultivated corn. Integrating teosinte’s genetic resources can contribute to developing more resilient and adaptable maize varieties for global food security and sustainable agriculture.