Contrary to what many scientists thought, genetically modified (GM) corn has not yet spread to native maize crops in southern Mexico.

After analyzing tens of thousands of seeds from maize crops grown in 2003 and 2004, researchers from Mexico and the United States found no evidence of transgenes in these indigenous varieties.

The finding surprised the researchers, said Allison Snow (photo), a professor of evolution, ecology and organismal biology at Ohio State University . She helped lead the study that appears online this week in the Early Edition of the Proceedings of the National Academy of Sciences.

The study is the first published report to survey the frequency of transgenes in native varieties of maize.

Four years ago, researchers reported finding four cobs of GM maize in Oaxaca , the southern Mexican state where Snow and her colleagues conducted their work. And despite the government's ban on planting the genetically engineered grain, other unpublished studies confirmed that GM maize had spread to remote mountain villages in the region.

In a country whose culture and identity revolve heavily around maize, or corn – the crop was first developed here thousands of years ago – the thought of importing GM varieties that could contaminate native plants frightens many citizens.

“The genetic diversity of native maize is an important resource with great cultural significance,” Snow said. “If farmers think that their highly revered native plants have been altered by transgenes, they might even stop planting them.”

“No one knew how common transgenic corn was in this area, we thought it could be as high as 5 to 10 percent,” Snow said. “There is great potential for transgenes to come across the U.S. border, with millions of tons of GM grain imported each year for processed food and animal feed.”

In 1998, the Mexican government imposed a six-year moratorium on the release of genetically modified maize in the country. However, farmers in Mexico are allowed to grow genetically engineered crops such as cotton and soybeans.

Over the two-year study, the researchers gathered more than 153,000 seeds from 870 maize plants in 125 fields in Oaxaca . They sent these seeds to two commercial companies in the United States that can test for very low concentrations of transgenic material in maize seeds.

The researchers were looking for traces of two key transgenes – one or both of which are found in all GM maize crops. Test results showed no evidence of the presence of either transgene from any of the seeds.

“We now know that transgenic maize isn't growing in Oaxaca ,” Snow said. “Mexican farmers who don't want transgenes in their crops will be relieved to find out that these uninvited genes seem to have disappeared.”

Transgenes that were present in Oaxaca prior to this study simply may not have survived, Snow said. Modern GM varieties may not be very hardy in Oaxaca, even if they can mate with local plants and gain a degree of hardiness that way.

“Indigenous maize grows mainly in the mountains – the climate and soils can be pretty harsh there,” she said. “Also, the influx of transgenic seeds may have declined if farmers became aware of the issue and took extra precautions with their seed stocks.”

The Mexican government might approve the cultivation of GM maize at some point in the future – meanwhile, transgenic seeds can easily enter Mexico from the United States, and more cases of wandering transgenes seem likely.

Snow conducted the work with scientists from the Instituto Nacional de Ecologia (SEMARNAT) and the National Commission for the Knowledge and Use of Biodiversity (CONABIO ), both in Mexico City; and from Genetic ID North America, Inc., in Fairfield, Iowa.

This research was supported in part by the College of Biological Sciences at Ohio State and by the Global Environmental Facility (GEF).