Researchers have tracked the spread of genes from genetically modified (GM) grass plants to measure how far wind carries their pollen. They report in a paper published online today by the Proceedings of the National Academy of Sciences that the modified genes appeared in normal plants up to 21 kilometers away, and also showed up in close relatives of the original plants. The results bolster concerns about the unintentional spread of genes from GM crops.

The team took advantage of a test field of creeping bentgrass several square kilometers in size that lawn-care giant Scotts planted in Oregon in 2003. The test plants were genetically modified to resist the popular herbicide glyphosate, marketed as Roundup. Creeping bentgrass, Agrostis stolonifera L., carpets golf courses worldwide, but the plant and its close relatives also grow wild in most of the U.S.

To assess how far GM pollen spreads, the scientists placed more than 100 "sentinel" plants at various distances from the test field. After the pollination season, they gathered and raised seeds from the sentinel plants and from related plants growing wild in the same area. Seedlings that survived exposure to Roundup were tested to confirm the protein and genetic signatures of the modification. The modified genes were most prevalent in plants grown from seeds collected within a few kilometers of the test field, but plants carrying GM genes also grew from seeds found as far as 21 kilometers away--much farther than previously reported. Lead author Lidia Watrud of the U.S. Environmental Protection Agency says that the small, easily blown grass pollen and the large scale of the test field helped the researchers to see the effect at such long distances. "If anything that's an underestimate," she adds, because there were no test plants farther away. Wild plants belonging to the same species and to a different species in the same genus also acquired the modified gene.

The U.S. grows many GM crops, including food crops, but most of them are not thought to cross-pollinate with wild relatives. In Europe and other countries, however, there is widespread opposition to GM crops. Although creeping bentgrass is not part of the food supply, some farmers are concerned that they would be unable to sell seeds that acquire the modified gene.

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