June 2012
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| Picture of conventional wheat Photo by User:Bluemoose (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC-BY-SA-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons |
Like the GM-concern groups, the
Guardian noted that, in contrast to past years, the media reporting
and comment have been “mostly neutral and positive about the
experiments, or actively hostile to the protester” and that the
scientists involved have “adopted a new tactic”. It, too, asked
“What has changed?”
To illustrate the new “reason and
openness”, the author described how keen the scientists had been to
'point out' that “the risk of pollen from their wheat reaching
surrounding crops is vanishingly small because the crop is
self-fertilising”. Thus, the logic continued, the urgency claimed
by the protesters to stop an open-air GM trial because it could have
profound effects on the environment “simply did not exist”.
Is this true?
There are two sources of GM pollen flow from the Rothamstead field trials to consider. One is the pollen produced by the GM crops in the test plots. The other will be produced by subsequent GM plants growing from the seed produced during the trial. Are both these dangers to the environment vanishingly small?
A Swiss paper, published in December
2011, mentions some important facts about past GM research, and goes
on to describe some very uncomfortable results of an experiment into
GM gene flow in wheat.
Conventional wheat tends to be
predominantly self-pollinating. This happens because fertilisation
of the flower usually happens before it opens. Add to this that the
flowers are only open to release or accept pollen for a very
restricted period time and their pollen is heavy enough not to be
carried far by a normal wind. Cross pollination is usually
restricted to 1-2% in very close proximity (less than a meter)
to the pollen-donating plant. These facts form the basis for the
Rothamstead scientists' dismissal of any potential for gene pollution
emanating from their GM trial.
However, there are “large differences
among wheat cultivars concerning pollen-mediated gene flow”. The
GM wheat team admit that their novel crop can out-cross at a
higher-than-normal rate of 4-5%, and other scientific studies have
found that direct contact between plants can achieve up to 10%
cross-fertilisation. Also, successful pollination by conventional
wheat pollen has been recorded at a distance of 2.75 kilometers from
its source plant.
The Swiss paper notes “It is usually
assumed that GM-wheat would behave similar to conventional varieties,
but only scant evidence corroborates this standpoint”. In other
words there is not only a known, very large, variation in the
tendency for cross-pollination amongst different conventional breeds
of wheat, but no one's ever done the science to check if GM wheat
behaves anything like its counterpart.
To fill this knowledge gap, the Swiss
researchers devised a comprehensive experiment. They created a range
of GM lines containing genes for fungus resistance plus their non-GM
sister controls, and used these to measure the extent of
cross-pollination arising from other GM and non-GM background crops.
What they found was that, on average,
3.36% of the seed from plants exposed to 'foreign' pollen were
cross-breeds: the worst-case recorded was actually 8.5%. In a real
field situation, pockets of contamination at 3.36% which would
continue to expand at that rate year-on-year isn't exactly
'vanishingly' small, and 8.5% definitely isn't. Over 14% of the
pollen-recipient plants had some degree of cross-fertilisation, while
the cross-pollinated seed produced by these plants amounted to nearly
a fifth of their total. The picture emerging here is that pollen
flow from wheat generally happens only over very short distances, but
when is does happen it's certainly not at a 'vanishingly'
small level.
The Swiss researchers noted that there
were not only clear physical differences between their GM strains
(all contained the same transgene inserted into the same parent
strain of wheat, but each was derived from a different transformation
event i.e. the novel gene had landed in a different location), but
the potential for gene flow turned out to be equally diverse. One GM
strain cross-fertilised at over six times the rate of its
non-GM equivalent. These variations may be explained by differences
in flower and pollen morphology and physiology, susceptibility to
infection, plant height etc., but what's more to the point, the
genetic transformations produced individuals which were physically
and physiologically unpredictable: no generalisations based on
conventional wheat characteristics can be made about their GM
relatives.
The Swiss team concluded from their
experiment that “it may be difficult to develop universal models
for pollen-mediated gene flow in wheat. Our results suggest that a
case-by-case approach will be required instead”.
To go back to the two sources of pollen
flow from the Rothamstead trial. Most of the pollen produced in the
trial (source No.1) will stay in the stand. However, the Swiss study
found that the gene-flow it recorded happened in the opposite
direction to the prevailing wind. Local gusts are clearly a very
important determinant of pollen movement within wheat stands. And,
given the wild weather Britain has been experiencing this year, the
possibility of the odd cloud of grains riding the wind to reach, and
pollinate, wheat farther afield can't be ruled out.
Regarding source No.2, no matter how
rigorous the 'clean up' procedure in the test plots, small quantities
of seeds from the trial field have a high chance of re-emerging
somewhere in Britain.
Even the Rothamstead scientists admit
that “dispersal of seed prior to harvest (is) possible by
wildlife”: GM seed can hitch a ride in or on birds and other small
animals. Spillage is also inevitable. Wherever it ends up, some GM
seed may lie dormant to emerge in future years.
Once any of these things have happened,
the offspring of the resulting rogue GM plant could generate over 8%
GM seeds in any wheat nearby, year on year. Be mindful that the
global rice contamination with experimental GM genes came from a
small-scale field test many years previously (rice is also reckoned
to present a 'low risk' of cross-fertilisation because it's
predominately self-pollinating with short-lived pollen and no known
insect pollinators); and, how it started is anybody's guess. The
short-term risk of gene pollution may be vanishingly small, but the
long-term risk is very real, very tangible and is being ignored by
the Rothamstead scientists.
There was another unexpected, and very
ominous, finding by the Swiss team. They demonstrated a tendency for
the GM plants to cross-fertilise preferentially with other GM
plants (and vice versa), leading to 'natural ...
pyramiding' of transgenes. Indeed, “The proportion of GM plants
within a population is therefore likely to increase.” The bottom
line here is that GM wheat of any kind may be dangerous to
commercialise because of the increased risk that novel transgenic
varieties will be generated.
The future 'pyramiding' of genes
threatened by the current GM trial involves two
antibiotic-resistance genes (at least one of which compromises the
efficacy of an antibiotic still in clinical use and known to
cross-react with other such life-saving drugs), plus a
herbicide-tolerance gene besides entirely artificial DNA constructs
which produce a wildlife-disrupting insect-smell.
OUR COMMENT
In summary, pollen flow from wheat can
happen, especially over short distances. Within a crop such local
levels of pollution are not vanishingly small. In the
long-term, the gene pollution arising from a few rogue GM plants gone
to seed would not only become significant, but would have a habit of
creating novel and unpredictable GM plants.
The suggestion that the protesters are
raising a needless alarm about an immediate threat to the environment
because wheat is self-fertilising is simplistic, wrong and designed
to mislead. The Rothamstead scientists who are acting with such
'reason and openness' have in reality been disseminating a
scientifically-baseless assumption about the potential for GM gene
flow.
SOURCES:
- Silvan Rieben, et al., 2011, Gene Flow in Genetically Modified Wheat, PLoS ONE, 6:12, December 2012
- James Randerson, The GM debate is growing up, Guardian 30.05.12
- GM Wheat: Cross-pollination and contamination, GM Freeze, 3.05.12
- Behind the GM Wheat Trial, Institute of Science in Society Report, 20.06.12
- GM rice trial, CSIRO Plant Trial Application DIR 052/2004, approved 2005
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