GMOs Invade Non-GMO Mexico

BERKELEY, Calif.--Some varieties of corn native to rural Oaxaca, Mexico have been found to contain genetically modified (GM) DNA, according to researchers at the University of California (UC) here, who reported their findings in the November 29 issue of Nature (414:541-43, 2001) (www.nature.com). The biotech DNA was discovered as researchers compared indigenous corn with samples of GM-free and GM corn varieties.

"This is very serious," said Ignacio Chapela, assistant professor of microbial ecology in UC Berkeley's department of environmental science, policy and management. "Because the region where our samples were taken is known for its diverse varieties of native corn."

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, according to Chapela.

The Mexican corn samples, called criollo, were taken from fields in Sierra Norte de Oaxaca. Non-GM control samples were obtained from blue maize grown in the Cuzco Valley of Peru, and from a collection of seeds from the Sierra Norte de Oaxaca region taken in 1971. GM-positive control samples--obtained from leftover stock of the U.S. 2000 planting season--included bulk grain samples of Yieldgard Bacillus thuringiensis (Bt)-maize (Bt1; Monsanto Corp.) and Roundup-Ready maize (RR1; Monsanto Corp.). Scientists studied all samples using polymerase chain reaction (PCR)-tests, checking for elements of transgenic DNA constructs that are used when bioengineered genes are introduced into a plant genome.

Results indicated that the Peruvian corn and the 1971 corn seeds were indeed clear of transgenic DNA. However, in four out of six samples of the criollo corn, clear evidence of p-35S (a promoter from the cauliflower mosaic virus often used in transgenic crops) was found. When scientists sequenced the DNA of the transgenic-positive plants, they found similarities to commercial transgenic crops.

In addition, two of the six criollo samples tested positive for the nopaline synthase terminator sequence (T-NOS) from Agrobacterium tumefasciens, which is another sign of transgenic contamination. An additional criollo sample also tested positive for the cry-1A gene of Bacillus thuringeiensis (Bt), the insecticidal bacterium that kills pests feeding on corn.

"I repeated the tests at least three times to make sure I wasn't getting false-positives," said David Quist, lead author and UC Berkeley graduate student in environmental science, policy and management. "It was initially hard to believe that corn in such a remote region would have tested positive."

Chapela and Quist hypothesized that the contamination came from multiple pollinations over a period of time. They identified the DNA fragments flanking the CMV promoter sequence through inverse PCR tests. Those fragments were diverse, which suggested random contamination as opposed to intentional genetic modification.

"If this contamination was the result of a single gene transfer event, we would expect to find the transgenic DNA in a consistent location on the criollo genome," Quist said. "Instead, we're finding it at different points along the genome."