Discovery in the Peruaçu Valley reinforces theory about corn domestication in South America

Researchers from USP and Embrapa found samples of semi-domesticated corn in caves in the Peruaçu Valley, Minas Gerais. The discovery was published in the journal Science Advances. These are the most distant samples ever found from the plant's center of origin, in Mexico. The discovery supports the theory that corn domestication may also have been completed in South America, and not just in Mexico, as previously thought.

The research reinforces the results published in 2018, which already pointed to genetic evidence that corn could have completed its domestication process in South America. However, archaeological evidence to confirm this theory was lacking. The samples discovered in the Peruaçu Valley include cobs, straw and grains excavated in 1994 by researchers from UFMG, but until then interpreted as already domesticated corn that did not grow properly.

Researcher Flaviane Malaquias Costa, from USP, explained that the samples, after further analysis, showed characteristics in common with teosinte, a plant that gave rise to corn in Mexico around 9 thousand years ago. The samples found in the Peruaçu Valley are between 1.010 and 500 years old, a period that coincides with the arrival of Europeans in America.

The samples are the most distant from the center of origin of corn ever found, at a distance of about 7.150 kilometers from Mexico and 2.300 kilometers from the southwest of the Amazon, a region where corn arrived about 6 years ago. Fábio de Oliveira Freitas, from Embrapa, highlighted the importance of the indigenous populations that selected and managed the corn, resulting in the current breeds.

The analyses of samples from the Peruaçu Valley revealed similarities with the Brazilian breed Entrelaçado, found in Acre and Rondônia. Elizabeth Ann Veasey, from USP, recalled that the selection of these populations contributed to the emergence of corn breeds in South America. A total of 296 samples were analyzed, including cobs, straw and grains.

The researchers used morphological characteristics to differentiate domesticated corn from semi-domesticated corn. One important marker is the number of grain rows. Primitive plants, such as teosinte, have fewer than eight rows, while current breeds can have between eight and 26. The Peruaçu samples have four to six rows, indicating their primitive nature.

The research is now entering a new phase, with archaeogenetic analyses in collaboration with international partners. If successful, these analyses could sequence the complete genome of the samples, revealing precise details about their kinship.

The finding also has geopolitical implications, as it reinforces the idea that some corn breeds were domesticated in Brazil, which may require new conservation efforts and rights in international treaties.

The caves of the Peruaçu Valley, in addition to housing cave paintings of cultivated species, such as corn, also served as burial sites, where baskets of corn were buried as offerings. The discovery sheds new light on the history of corn domestication and the role of indigenous populations in maintaining the plant's genetic resources.

The researchers' article can be read at doi.org/10.1126/sciadv.adn1466