Bioengineered DNA discovered in native Mexican corn, researchers report

By Sarah Yang, Public Affairs

05 December 2001 | Native varieties of corn grown in remote regions of Mexico have been contaminated by DNA from genetically modified crops, a finding that has both surprised and dismayed the campus researchers who made the discovery.

"This is very serious because the region where our samples were taken are known for their diverse varieties of native corn, which is something that absolutely needs to be protected," said Ignacio Chapela, assistant professor of microbial ecology in the College of Natural Resources' Department of Environmental Science, Policy & Management.

In the study, published Nov. 29 in the journal Nature, Chapela and lead author David Quist, a graduate student, compared indigenous corn with samples known to be free from genetic engineering as well as with genetically modified varieties.

The native corn, or "criollo," samples were taken from four fields in the remote, mountainous region of Sierra Norte de Oaxaca. Control samples that had not been genetically modified came from blue maize grown in the Cuzco Valley in Peru. They also came from a collection of seeds from the Sierra Norte de Oaxaca region taken in 1971, before the advent of genetically modified, or transgenic, crops.

Using highly sensitive tests, the researchers checked for transgenic DNA constructs used when bioengineered genes are introduced into a plant genome.

They found no signs of transgenic DNA in the Peru and 1971 seed collections. In the criollo samples, however, four out of six samples tested showed weak but clear evidence of a promoter from the cauliflower mosaic virus widely used in transgenic crops.

Chapela and Quist said the contamination likely came from multiple pollinations over time.

The researchers first detected the transgenic DNA in October 2000 while working with the Mycological Facility in Oaxaca, a locally run biological laboratory where Chapela serves as the scientific director. Chapela alerted the Mexican government, which proceeded to conduct its own tests; it found transgenic DNA in three to 10 percent of the Sierra Norte de Oaxaca maize.

Just how the contamination occurred remains a puzzle. Agricultural experts and proponents of biotech crops maintain that corn pollen is heavy, so it doesn't blow far from corn fields. Chapela said this assumption may need to be reevaluated in light of the recent findings in Mexico.

Mexico imposed a moratorium in 1998 on new plantings of transgenic maize. The closest region where bioengineered corn was ever known to have been planted is 60 miles away from the Sierra Norte de Oaxaca fields, said Chapela.

The new findings are almost certain to fuel the already contentious debate over the use of genetically modified crops. Proponents of transgenic agriculture say biotechnology helps to increase crop yields to help feed the world, improve the food's nutritional value and reduce the use of pesticides.

Opponents say not enough is known about the health and ecological effects of biotech crops and that the risks outweigh the benefits.

To date, more than 30 million hectares of transgenic crops are report to have been grown.

Genes from genetically modified crops that spread unintentionally can threaten the diversity of natural crops by crowding out native plants, said Chapela. A wealth of maize varieties, cultivated over thousands of years in the Sierra Norte de Oaxaca region, provide an invaluable "bank account" of genetic diversity, he said. Chapela added that genetically diverse crops are less vulnerable to disease, pest outbreaks and climatic changes.

"We can't afford to lose that resource," he said.