Modified rape crosses with wild plant to create tough pesticide-resistant
Modified genes from crops in a GM crop trial have transferred into local wild
plants, creating a form of herbicide-resistant "superweed", the Guardian
The cross-fertilisation between GM oilseed rape, a brassica, and a distantly
related plant, charlock, had been discounted as virtually impossible by scientists
with the 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
The five scientists from the Centre for Ecology and Hydrology, the government
research station at Winfrith in Dorset, placed their findings on the department's
website last week.
A reviewer of the paper has appended to its front page: "The frequency
of such an event [the cross-fertilisation of charlock] in the field is likely
to be very low, as highlighted by the fact it has never been detected in numerous
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 specialist
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."
Dr 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".
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 an average of 103,000 plants, Dr 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 Dr Johnson points out that the plant was very large and produced many flowers.
He said: "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 neighbourhood,
spreading the GM genes in that way. This is after all how the cross-fertilisation
between the rape and charlock must have occurred in the first place."
Since charlock seeds can remain in the soil for 20 to 30 years before they
germinate, once GM plants have produced seeds it would be almost impossible
to eliminate them.
Although the government has never conceded that gene transfer was a problem,
it was fear of this that led the French and Greek governments to seek to ban
Emily Diamond, a Friends of the Earth GM researcher, said: "I was shocked
when I saw this paper. This is what we were reassured could not happen - and
yet now it has happened the finding has been hidden away. This is exactly what
the French and Greeks were afraid of when they opposed the introduction of GM
The findings will now have to be assessed by the government's Advisory Committee
on Releases to the Environment (Acre). The question is whether it is safe to
release GM crops into the UK environment when there are wild relatives that
might become superweeds and pose a serious threat to farm productivity. This
has already occurred in Canada.
The discovery that herbicide-resistant genes have transferred to farm weeds
from GM crops is the second blow to the hopes of bio-tech companies to introduce
their crops into Britain. Following farm scale trials there was already scientific
evidence that herbicide-tolerant oilseed rape and GM sugar beet were bad for
biodiversity because the herbicide used to kill the weeds around the crops wiped
out more wildlife than with conventionally grown crops. Now this new research,
a follow-up on the original trials, shows that a second undesirable potential
result is a race of superweeds.
The findings mirror the Canadian experience with GM crops, which has seen farmers
and the environment plagued with severe problems.
Farmers the world over are always troubled by what they call "volunteers"
- crop plants which grow from seeds spilled from the previous harvest, of which
oilseed rape is probably the greatest offender, Anyone familiar with the British
countryside, or even the verges of motorways, will recognise thousands of oilseed
rape plants growing uninvited amid crops of wheat or barley, and in great swaths
by the roadside where the "small greasy ballbearings" of seeds have
spilled from lorries.
Farmers in Canada soon found that these volunteers were resistant to at least
one herbicide, and became impossible to kill with two or three applications
of different weedkillers after a succession of various GM crops were grown.
The new plants were dubbed superweeds because they proved resistant to three
herbicides while the crops they were growing among had been genetically engineered
to be resistant to only one.
To stop their farm crops being overwhelmed with superweeds, farmers had to
resort to using older, much stronger varieties of "dirty" herbicide
long since outlawed as seriously damaging to biodiversity.
Q&A: What the discovery means for UK farmers
What's the GM situation in the UK?
No GM crops are currently grown commercially in the UK. Companies who wish
to introduce them face a series of licensing hurdles in Britain and Europe and
interest has waned in recent years amid public opposition.
Other firms have dropped applications in the wake of the government field scale
trials that showed growing two GM varieties - oilseed rape and sugar beet -
was bad for biodiversity.
The EU has approved several GM varieties and the UK government insists that
applications will be considered on a case-by-case basis.
Where are GM crops grown?
Extensively in the wide open spaces of the US, Canada and Argentina. In Europe,
Portugal, France and Germany have all dabbled with GM insect-resistant maize.
Spain plants about 100,000 hectares (250,000 acres) of it each year for animal
What is a superweed?
Many GM crop varieties are given genes that allow them to resist a specific
herbicide, which farmers can then apply to kill the weeds while allowing the
GM crop to thrive.
Environmental campaigners have long feared that if pollen from the GM crop
fertilised a related weed, it could transfer the resistance and create a superweed.
This "gene transfer" is what appears to have happened at the field
scale trial site. It raises the prospect of farmers who grow some GM crops being
forced to use stronger herbicides on their fields to deal with the upstart weeds.
Is it a big problem?
Not yet. Farmers in the UK do not grow GM crops commercially. If they did,
then the scale of possible superweed contamination depends on two things: whether
the hybrid superweed can reproduce (many hybrids are sterile) and, if it could,
how well its offspring could compete with other plants. Herbicide-resistant
weeds could potentially grow very well in agricultural fields where the relevant
herbicide is applied. Most experts say superweeds would be unlikely to sweep
across the UK countryside as, without the herbicide being used to kill their
competitors, their GM status offers no advantage.
Some GM crops, such as maize, have no wild relatives in the UK, making gene
transfer and the creation of a superweed from them impossible.
Is it a surprise?
On one level no, gene flow and hybridisation are as old as plants themselves.
Short of creating sterile male plants, it's simply impossible to stop crops
releasing pollen to fertilise related neighbours. But government scientists
had thought that GM oilseed rape and charlock were too distantly related for
it to occur.
The dangers of hybridisation where it does happen are well documented - experts
from the Dorset centre behind the latest research published a high-profile paper
in 2003 in the US journal Science showing widespread gene flow from non-GM oilseed
rape to wild flowers.
Have superweeds surfaced elsewhere?
Farmers in Canada and Argentina growing GM soya beans have large problems with
herbicide-resistant weeds, though these have arisen through natural selection
and not gene flow through hybridisation. Experiments in Germany have shown sugar
beets genetically modified to resist one herbicide accidentally acquired the
genes to resist another - so called "gene stacking", which has also
been observed in oilseed rape grown in Canada.