Environmentalists' concerns that genetically engineered plants could result in "superweeds" which were immune to weedkillers have been scientifically upheld, according to Genetic Concern.
The group, which lobbies against the release of genetically modified plants, says findings published in the latest issue of Nature support its warning about genetically modified plants.
The findings show that a genetically modified plant was much better at transferring its engineered genes into neighbouring plants than similar wild or cross-bred versions of the plant.
The findings, published as a letter headed "Promiscuity in Transgenic Plants", describes research by Joy Bergelson, Colin Purrington and Gale Wichmann of the department of ecology and evolution at the University of Chicago.
The group planted 144 Arabidopsis thaliana plants including wild, cross-bred and genetically modified forms. The cross-bred and modified plants were both herbicide resistant and the researchers were trying to establish if either would fertilise wild versions and move their herbicideresistant genes across.
The engineered versions "showed a dramatically increased ability to donate pollen to nearby wild-type mothers" compared to the cross-bred plants, the researchers wrote. A survey of 100,000 resultant seeds showed that cross-bred fathers transferred herbicide resistance in 0.3 per cent of the total, compared with almost 6 per cent for transgenic fathers.
The "results show that genetic engineering can substantially increase the probability of transgene escape", the researchers concluded. "Because we do not know the underlying genetic mechanism, the generality of our result is unclear at present," they said.
The results were, however, of "broad relevance because this transgene has been introduced into dozens of agricultural crops".
"Such findings confirm the widely held view that genetic engineering produces unpredicted side-effects," said Mr Quentin Gargan of Genetic Concern. The group has called for a moratorium on the intentional release of modified plants.
It is also involved in court action to prevent the US multinational Monsanto from continuing field trials in Ireland of a modified sugar beet that is herbicide resistant.
The head of Monsanto in Ireland, Dr Patrick O'Reilly, said yesterday that transgenic plants are tested for a whole range of traits before they are put forward for possible release.
"While we are not familiar with the details of this experiment, it is absolutely certain that a plant which exhibited these traits in the laboratory would either be eliminated as a candidate for consideration or would be closely scrutinised by the regulatory authorities before even a field trial permit was granted."
