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Transgenic DNA Found in Mexican Maize

28 November 2001 (All day)
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Modified maize. These traditional varities of corn contain transgenic DNA.

Scientists have discovered DNA from genetically engineered crops in a wild variety of corn grown in rural Mexico. While there's no evidence that the transgenic DNA will harm people or the genetic diversity of the crops, experts are surprised by the find and say it highlights the challenge of preventing the spread of transgenic DNA beyond the crops to which it's originally added.

"This is a tremendously important study," says Norman Ellstrand of the University of California, Riverside. "It really changes our view on [containing] genetic material. One can only assume that, with globalization, it will become more difficult."

The work, by David Quist and Ignacio Chapela, microbial ecologists at the University of California, Berkeley, explores the extent to which genes are exchanged between industrial crops and their wild relatives. The researchers tested for transgenic DNA in whole cobs of native corn grown by traditional farmers in Oaxaca, Mexico. "To our surprise, we found that contamination is frequent and diverse," Quist says.

As they report in the 29 November issue of Nature, the foreign DNA included a promoter from the cauliflower mosaic virus and other constructs used to make transgenic crops. The pair also detected the bacterial cry1Ab gene, which produces the so-called BT toxin and helps corn resist moth caterpillars. A similar, unpublished study conducted at the same time by scientists from Mexico's National Institute of Ecology and the National Commission of Biodiversity found that up to 10% of kernels contained transgenic DNA.

Where did the DNA come from? Transgenic corn had been planted in Mexico before a moratorium in 1998. But the sample locations were 100 kilometers from the closest source. Transgenic corn is still imported from the U.S. for human and animal food, however, and Quist suspects that local farmers are planting the imported corn and crossing it with their own varieties.

It's not clear what impact the introduction of this DNA might have. "The ecological studies haven't been done," says Quist, who nevertheless worries about a potential loss of genetic diversity. Other scientists are not alarmed, however. "I don't think a few additional transgenes would have any major effects on the genetic diversity of these plants," says Allison Snow of Ohio State University in Columbus.

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References for gene flow and transgenic crops

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