Superweeds Encouraged by GM Crops

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Friday, 16 August 2002

Weeds become stronger and fitter by cross-breeding with genetically engineered crops, US researchers have shown for the first time. And at the same time, a team in France has demonstrated how easily weeds might be able to swap genes with the GM strains of sugar beet already in field trials.

Allison Snow's team at Ohio State University showed in controlled tests that wild sunflowers, considered a weed by many farmers in the US, become hardier and produce 50 per cent more seeds if they are crossed with a GM sunflower resistant to seed-nibbling moth larvae. "We were shocked," says Snow.

Snow, whose results were presented to a conference last week, cautions against overstating the significance of the results. "It doesn't prove all GM crops are dangerous," she says. "I just think we need to be careful because genes can be very valuable for a weed and persist for ever once they're out there."

Studies of normal beet fields by Henk van Dijk and his colleagues at the University of Lille in France suggest that they have underestimated the likelihood of GM beets swapping genes with the beet weeds that grow among them. "We found gene flow to be possible between all forms," they write in the Journal of Applied Ecology.

The situation with beet is particularly complicated because there is a two-way flow, with weed genes often polluting farm strains and reducing yields. The beet weeds could become even more of a nuisance to farmers if they pick up herbicide-resistance genes.

Van Dijk says that while tricks such as doubling the number of chromosomes in GM strains could reduce the chance of gene spread, they would not eliminate it. "It's almost inevitable," he says. But despite the risk, he still believes GM strains could help farmers.

Source: Andy Coghlan New Scientist 15 Aug 02