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February 28, 2002


Has GM Corn ëInvadedí Mexico?


Has GM Corn ëInvadedí Mexico?

ñCharles C. Mann, Science Vol 295, p1617; March 1, 2002

On Thursday, 21 February, the gene wars took a stunning new twist, or so
it seemed. Mexican newspapers reported that two teams of government
researchers had confirmed University of California (UC), Berkeley,
biologist Ignacio Chapelaís explosive findings: that transgenic corn was
growing in Mexico, the heartland of maize diversity.

Yet even as Chapela was proclaiming this news at a Mexico City press
conference, a scathing editorial in the February issue of Transgenic
Research was crisscrossing the globe by e-mail. In it, editor Paul
Christou charged that Chapela and his coauthor, UC Berkeley graduate
student David Quist, had presented ìno credible evidence Ö to justify any
of [their] conclusions.î Meanwhile, Nature, which published the
Quist-Chapela paper last November, was weighing the publication of no
fewer than four biting critiques of the article. Adding to the muddle,
Elena Alvarez-Buylla Roces, a biologist at the National Autonomous
University of Mexico who appeared with Chapela at the press conference,
insisted in a later e-mail to Science that Mexican investigators ìstill do
not have definite answers towards corroborating or not [corroborating]
Chapelaís results.î

Welcome to the ìmaize scandal,î which is driving the battle over
genetically modified (GM) crops to new heights of acrimony and confusion.
Widely circulating anonymous e-mails accuse Chapela and Quist of conflicts
of interest and other misdeeds. Meanwhile, 144 civil-society groups have
leapt to the authorsí defense, asserting in a joint statement on 19
February that the biotech industry is using ìintimidatoryî techniques to
ìsilenceî dissident scientists. ìIíve never seen anything like it,î says
Peggy Lemaux, a UC Berkeley molecular biologist who is one of the most
public critics of the Quist-Chapela paper. ìThereís been a lot of fighting
about transgenics, but this is something else.î Still unclear, say many
scientists, is whether transgenic corn has indeed invaded Mexicoóand if
so, whether it poses a threat to one of the worldís most important

The furor began on 29 November, when Quist and Chapela reported that
transgenic maize genes had introgressed óskipped from one gene pool to
another ówith traditional strains (landraces) of maize in remote areas of
Oaxaca. The highlands of Oaxaca, Chiapas, and adjacent Guatemala are one
of seven ìcenters of genetic diversityî that spawned most of todayís
crops. To protect this diversity, an invaluable resource for crop
breeders, the Mexican government declared a moratorium in 1998 on planting
transgenic maize anywhere in the nation. Now the Nature paper was claiming
ìa high level of gene flowî from illegally planted transgenic maize to
local landracesóa process that Quist and Chapela argued could exert ìa
major influence on the future genetics of the global food system.î
Greenpeace and others opposed to biotechnology immediately called on the
Mexican government to ban transgenic U.S. maize, the presumed source of
the foreign genes. (Free-trade rules let transgenic maize be shipped into
Mexico but not grown there.) ìWorld food security depends on the
availability of this diversity,î Chapela told Newsweek in January. ìHaving
it contaminated is something humanity should worry about.î

Adding to the alarm, Quist and Chapela suggested that the transgenes were
unstable. The foreign genes, they wrote, often ìseemed to have become
re-assorted and introduced into different genomic backgrounds.î In other
words, when transgenic maize hybridized with landrace maize, the novel
genetic material broke up into chunks that jumped around the genome. The
implications were profound: Because a geneís behavior depends on its place
in the genome, the displaced DNA could be creating utterly unpredictable

Activistsí fears centered on the promoter sequenceóusually CaMV 35S, which
originates in the cauliflower mosaic virusóused to drive the activity of
newly inserted genes for, say, herbicide resistance. If the promoter broke
off during hybridization, it could conceivably take over other genes, with
unknown consequences. ìThe spread of the promoter could prove to be worse
than the spread of the genes for herbicide and insect resistance,î says
Peter Rosset, co-director of the Institute for Food and Development Policy
(Food First), a research group that advocates on behalf of small farmers.
ìIf true, this would be a red flag that would call into question every
other GM crop on the market.î

But Lemaux and other critics arenít buying it. ìTheyíre saying that the
[hybrid and introgressed] genomes were completely unstable all the time,î
she says. ìIíve worked with transgenic corn for 10 years, and Iíve never
seen anything like that.î To search for transgenic DNA, Quist and Chapela
took sample ears of maize from two locations in Oaxaca in October and
November 2000 and tested them using the polymerase chain reaction. PCR
amplification detects particular snippets of DNA by multiplying them to
observable levels. Unfortunately, notes molecular biologist Marilyn
Warburton of the Mexico-based International Maize and Wheat Improvement
Center (CIMMYT), PCR is so sensitive that minute traces of laboratory
contaminants can create false-positive results. ìIf you get a positive
result, you have to check it repeatedly,î

Warburton says. ìAnd even then you need to confirm it by another method to
be completely sure youíre not fooling your self.î Chapela and Quist did
not report performing such additional tests.

Motivated by these sorts of concerns, at least four groups of
researchersófrom the University of Washington, the University of Georgia,
and two from Quist and Chapelaís home base of UC Berkeleyósent sharply
critical letters to Nature in December. Three referees reviewed the
letters and recommended publication of one or more, accompanied by a
rebuttal from Quist and Chapela. ìThe PCR and iPCR [inverse PCR, a
variant] data presented is simply not sufficient data to warrant ANY of
the conclusions of the authors,î including both the presence of transgenic
DNA in Mexican maize and its instability, declared the first reviewer.
ìNature should demand that the authors retract their manuscript if they
cannot demonstrate well-controlled DNA blot analyses [a common
confirmatory test] documenting transgene integration events.î ìNature is
coming under pressure to use secondary technical criticisms to discredit
our main findings,î responds Quist. Regarding doubts about the instability
he reported, he believes that ìthe critique is coming from expectationsî
created by lab experiments ìthat arenít necessarily reflected in what you
see when you go out in nature.î To respond to criticisms, ìweíre
discussing with Nature the possibility of publishing [in a reply] some new
information that substantiates our findings.î

(Science obtained three of the letters, the initial Quist-Chapela
response, and some of the anonymous referee reports from sources other
than their authors, who are blocked by Nature from discussing their
critiques before publication. Nature editor Philip Campbell says the
journal acts ìas promptly as possibleî on criticisms, publishing them when

Surprisingly, even Quist and Chapelaís most strident critics agree with
one of their central points: Illicit transgenic maize may well be growing
in Mexico. In May 2001 Chapela shared his initial results with the
National Institute of Ecology (INE, the research arm of the Mexican
Ministry of the Environment and Natural Resources) and the interagency
National Biodiversity Council (CONABIO). Concerned, INE and CONABIO took
maize samples from 20 random locations in Oaxaca and two in the adjacent
state of Puebla. The samples were divided into two groups and
independently analyzed by researchers at the National Autonomous
University of Mexico and the Center for Investigation and Advanced Studies
(CINVESTAV) at the National Polytechnic Institute. At a 23 January meeting
in Mexico City, CINVESTAV official Elleli Huerta presented preliminary PCR
findings indicating that transgenic promoters, mostly CaMV 35S, were
present in about 12% of the plants.

In some areas, up to 35.8% of the grain contained foreign sequences, INE
scientific adviser Sol Ortiz Garcia told Science last week. According to
Ortiz, both the INE lab and the National Autonomous University of Mexico
labs are still ìdouble-checkingî the findings. The possible corroboration,
Alvarez- Buylla Roces says, is ìonly based on PCR tests and [is]
preliminary.î Indeed, says Timothy Reeves, director-general of CIMMYT,
which is working with the Mexican government, the two Mexican teams are
now responding to the criticism of PCR methodology by revamping their
analyses to include bigger samples and more reliable tests.

Meanwhile, CIMMYT, which develops improved crops for Third World farmers,
has been searching its vast storehouse of maize varieties for transgenic
ìcontamination.î By 22 February, the lab had found none, and the
organization has adopted measures that it believes will prevent GM maize
from entering its gene bank, preserving at least some of Mexicoís maize
diversity. But given the amount of transgenic maize in the United States,
Reeves believes it is ìvery likelyî that some will eventually end up
growing in Mexico. For now, however, ìtransgenic maize in Mexico is still