GM crops created superweed, say scientists
Modified rape crosses with wild plant to create tough
Paul Brown, environment correspondent
Monday July 25, 2005
Modified genes from crops in a GM crop trial have transferred into
plants, creating a form of herbicide-resistant "superweed", the
The cross-fertilisation between GM oilseed rape, a brassica, and a
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
The new form of charlock was growing among many others in a field which
used to grow GM rape. When scientists treated it with lethal herbicide
Unlike the results of the original trials, which were the subject of
press briefings from scientists, the discovery of hybrid plants that
a serious problem to farmers has not been announced.
The scientists also collected seeds from other weeds in the oilseed
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
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
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
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
taken place the new plant has a huge selective advantage. That plant
Dr Johnson, who is head of the biotechnology advisory unit and head of
management technologies group at English Nature, the government nature
said: "Unlike the researchers I am not surprised by this. If you apply
to plants which is lethal, eventually a resistant survivor will turn
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
French researcher placed a single triazine-resistant weed, known as fat
maize fields where atrazine was being used to control weeds. After four
the plants had multiplied to an average of 103,000 plants, Dr Johnson
What is not clear in the English case is whether the charlock was
Scientists collected eight seeds from the plant but they failed to
them and concluded the plant was "not viable".
But Dr Johnson points out that the plant was very large and produced
He said: "There is every reason to suppose that the GM trait could be
plant's pollen and thus be carried to other charlock in the
spreading the GM genes in that way. This is after all how the
cross-fertilisation between the rape and charlock must have occurred in
Since charlock seeds can remain in the soil for 20 to 30 years before
germinate, once GM plants have produced seeds it would be almost
Although the government has never conceded that gene transfer was a
was fear of this that led the French and Greek governments to seek to
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
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
on Releases to the Environment (Acre). The question is whether it is
release GM crops into the UK environment when there are wild relatives
might become superweeds and pose a serious threat to farm productivity.
already occurred in Canada.
The discovery that herbicide-resistant genes have transferred to farm
GM crops is the second blow to the hopes of bio-tech companies to
their crops into Britain. Following farm scale trials there was already
scientific evidence that herbicide-tolerant oilseed rape and GM sugar
bad for biodiversity because the herbicide used to kill the weeds
crops wiped out more wildlife than with conventionally grown crops. Now
research, a follow-up on the original trials, shows that a second
potential result is a race of superweeds.
The findings mirror the Canadian experience with GM crops, which has
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
rape is probably the greatest offender, Anyone familiar with the British
countryside, or even the verges of motorways, will recognise thousands
oilseed rape plants growing uninvited amid crops of wheat or barley,
great swaths by the roadside where the "small greasy ballbearings" of
spilled from lorries.
Farmers in Canada soon found that these volunteers were resistant to at
one herbicide, and became impossible to kill with two or three
different weedkillers after a succession of various GM crops were grown.
The new plants were dubbed superweeds because they proved resistant to
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
resort to using older, much stronger varieties of "dirty" herbicide
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
introduce them face a series of licensing hurdles in Britain and Europe
interest has waned in recent years amid public opposition.
Other firms have dropped applications in the wake of the government
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
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
Portugal, France and Germany have all dabbled with GM insect-resistant
Spain plants about 100,000 hectares (250,000 acres) of it each year for
What is a superweed?
Many GM crop varieties are given genes that allow them to resist a
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
fertilised a related weed, it could transfer the resistance and create a
superweed. This "gene transfer" is what appears to have happened at the
scale trial site. It raises the prospect of farmers who grow some GM
forced to use stronger herbicides on their fields to deal with the
Is it a big problem?
Not yet. Farmers in the UK do not grow GM crops commercially. If they
the scale of possible superweed contamination depends on two things:
hybrid superweed can reproduce (many hybrids are sterile) and, if it
well its offspring could compete with other plants. Herbicide-resistant
could potentially grow very well in agricultural fields where the
herbicide is applied. Most experts say superweeds would be unlikely to
across the UK countryside as, without the herbicide being used to kill
competitors, their GM status offers no advantage.
Some GM crops, such as maize, have no wild relatives in the UK, making
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
Short of creating sterile male plants, it's simply impossible to stop
releasing pollen to fertilise related neighbours. But government
thought that GM oilseed rape and charlock were too distantly related
for it to
The dangers of hybridisation where it does happen are well documented -
from the Dorset centre behind the latest research published a
in 2003 in the US journal Science showing widespread gene flow from
oilseed rape to wild flowers.
Have superweeds surfaced elsewhere?
Farmers in Canada and Argentina growing GM soya beans have large
herbicide-resistant weeds, though these have arisen through natural
and not gene flow through hybridisation. Experiments in Germany have
beets genetically modified to resist one herbicide accidentally
genes to resist another - so called "gene stacking", which has also been
observed in oilseed rape grown in Canada.
· David Adam
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