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/Nature/ *436*, 760 (11 August 2005) | doi: 10.1038/436760a
Four years on, no transgenes found in Mexican maize
Emma Marris
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<http://www.nature.com/nature/journal/v436/n7052/full/436760a.html#top>
Abstract
Corn found to be free of GM contamination.
Four years ago, the discovery of transgenes from genetically modified
(GM) crops in traditional maize varieties in Oaxaca, Mexico, triggered
an almighty row. A new survey suggests that measures taken since then to
purge the crops of transgenes have been effective.
In the original paper, David Quist and Ignacio Chapela of the University
of California, Berkeley, used the polymerase chain reaction (PCR) to
detect two genetic sequences from GM maize in harvests from 2000 (D.
Quist and I. H. Chapela Nature 414, 541−543; 2001
<http://dx.doi.org/10.1038/35107068>). Using a variant of the technique
called inverse PCR, they also argued that the transgenes had integrated
throughout the genomes of Mexico's maize varieties.
This was a shocking result, as it suggested that the 'contaminated'
plants were not sporadic hybrids. Instead, it seemed that the transgenes
were entrenched in the traditional varieties at the centre of natural
genetic diversity for maize. "It was as if someone had gone to the
United Kingdom and started replacing the stained-glass windows in the
cathedrals with plastic," says Jorge Soberón, a former Mexican
government scientist now at the University of Kansas in Lawrence and a
co-author of the new study.
The inverse-PCR methodology used by Quist and Chapela soon came under
fire, however, and /Nature/ stated that it would not have published the
paper if the criticisms had cropped up while the paper was under review.
But even so, few experts questioned the basic finding that some
transgenes had flowed into Mexican maize.
Despite an official moratorium on GM planting, this could have resulted
from local farmers planting GM maize intended for food use that was
imported from the United States. Unpublished work by Mexican government
scientists also found transgenes, but a thorough and systematic
confirmation was lacking.
That survey has now been done — and to the surprise of the authors, they
found no transgenes at all. The sample of more than 150,000 seeds from
2003 and 2004 was negative for the same two transgenic sequences (S.
Ortiz-García /et al/. /Proc. Natl Acad. Sci. USA/
doi10.1073/pnas.0503356102; 2005). "I was convinced we were going to
verify Quist and Chapela's results," says co-author Exequiel Ezcurra,
head of the Biodiversity Research Center of the Californias at the San
Diego Natural History Museum and former president of the National
Institute of Ecology in Mexico City.
The authors speculate that transgenes were present in the fields in
2000, but dropped out of local maize varieties thanks to a programme of
education for farmers and a reduction in GM maize imports. The
researchers, led by Allison Snow of Ohio State University in Columbus,
did not directly replicate Quist and Chapela's inverse-PCR methods. But
Snow says that the apparent failure of the transgenes to persist down
the generations contradicts the idea that they were entrenched in the
genomes of the traditional maize varieties.
Brian Johnson, who follows developments in agricultural biotechnology
for the government conservation agency English Nature, is unsurprised by
this finding: "If there are transgenes in Mexico, or anywhere else, I
would expect that they would be difficult to find — they would be rather
sporadic." Johnson says he never believed they were permanently
incorporated into the genes of traditional maize varieties.
Chapela stands by his findings, saying it is "naive" to believe an
education programme could have such a dramatic effect. He claims that
the commercial labs used by the research team to do the screening used
conservative thresholds for declaring a match with the transgene
sequences. But Bernd Schoel, director of research at one of those labs —
Genetic ID of Fairfield, Iowa — says the screen was as sensitive as
possible, given the sample size.
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<http://www.nature.com/nature/journal/v436/n7052/full/436760a.html#top>
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