Modified genes from crops in a GM crop trial have transferred into local wild plants, creating a form of herbicide-resistant "superweed."
The cross-fertilization between GM oilseed rape and a distantly related plant, charlock, had been discounted as virtually impossible by scientists with the British government's environment department. It was found during a follow up to the government's three-year trials of GM crops which ended two years ago.
The new form of charlock was growing among many others in a field which had been used to grow GM rape. When scientists treated it with lethal herbicide it showed no ill-effects.
Unlike the results of the original trials, which were the subject of large-scale press briefings from scientists, the discovery of hybrid plants that could cause a serious problem to farmers has not been announced. The scientists also collected seeds from other weeds in the oilseed rape field and grew them in the laboratory. They found that two -- both wild turnips -- were herbicide resistant.
The five scientists from the Center for Ecology and Hydrology, the government research station at Winfrith in Dorset, placed their findings on the department's Web site last week.
A reviewer of the paper has appended to its front page: "The frequency of such an event [the cross-fertilization of charlock] in the field is likely to be very low, as highlighted by the fact it has never been detected in numerous previous assessments." However, he adds: "This unusual occurrence merits further study in order to adequately assess any potential risk of gene transfer."
Brian Johnson, an ecological geneticist and member of the government's scientific group which assessed the farm trials, has no doubt of the significance.
"You only need one event in several million. As soon as it has taken place the new plant has a huge selective advantage. That plant will multiply rapidly," he said.
Johnson, who is head of the biotechnology advisory unit and head of the land management technologies group at English Nature, the government nature advisers, said: "Unlike the researchers I am not surprised by this. If you apply herbicide to plants which is lethal, eventually a resistant survivor will turn up."
The glufosinate-ammonium herbicide used in this case put "huge selective pressure likely to cause rapid evolution of resistance," he said.
To assess the potential of herbicide-resistant weeds as a danger to crops, a French researcher placed a single triazine-resistant weed, known as fat hen, in maize fields where atrazine was being used to control weeds. After four years the plants had multiplied to 103,000 plants, Johnson said.
What is not clear in the English case is whether the charlock was fertile. Scientists collected eight seeds from the plant but they failed to germinate them and concluded the plant was "not viable."
But Johnson points out that the plant was very large and produced many flowers.
"There is every reason to suppose that the GM trait could be in the plant's pollen and thus be carried to other charlock in the neighborhood, spreading the GM genes in that way. This is after all how the cross-fertilization between the rape and charlock must have occurred in the first place," he said.
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