Genetically-modified crops are not only spreading into the wild but also managing to survive and reproduce, according to a US study.
Researchers from the University of Arkansas travelled along more than 3,000 miles of roads in North Dakota, USA, stopping every five miles to collect roadside weeds. 46 per cent of their sample locations contained canola (similar to oil seed rape grown in the UK) growing in the wild, of which 83 per cent contained genes from genetically modified strains of the crop.
Most of the canola grown in the region is genetically-modified to be resistant to herbicides, and produced by the biotech giants Monsanto and Bayer.
The findings have raised fears that genes could be escaping into the wild and speeding the evolution of herbicide-resistant weeds, so-called super-weeds.
The biotech industry has been quick to downplay the concerns, saying that GM crops don't survive well in the wild.
'They [GM plants] are man-made crops and when it comes to competing with their wild counterparts they are lousy and do not do very well at all,' sid Dr Julian Little, spokesperson for the industry lobby group the Agricultural Biotechnology Council (ABC).
'Most plants do not survive into maturity and shed seed themselves. They do occasionally, but over one or two seasons it becomes less and less relevant, which is why in places like field margins we tend not to see crops growing,' he added.
However, the researchers said their findings showed that the wild populations were actually 'established' and 'competing' in the wild.
'Technically, these plants are not supposed to be able to compete in the wild. The fact that we found two plants that were resistant to two types of herbicide (seeds of this nature have not been commercially released), leads us to believe that these plants have been around for at least two generations,' says study co-author Meredith Schafer, adding that studies in Canada and Japan had showed populations lasting for up to eight years.
Much of the wild canola is suspected to be the result of seed spill from agricultural transportation, but researchers said thousands of acres of GM canola went unharvested every year - leaving approximately eight billion seeds in North Dakota alone that can 'easily be blown around and cross-pollinate'.
The researchers, who presented their findings to the Ecological Society of America last week, said once these seeds become established in wild populations it would become increasingly difficult to get rid of them using current herbicides.
Co-author Professor Cynthia Sagers said the spread of herbicide resistance in wild plants should now be taken more seriously by US regulators.
Monsanto said it provides farmers with information on how to control canola but that most roadside canola could best be dealt with by mowing.
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