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Dear friends,
here the comments of John Hodgson about the Mexican gene flow case.
I wish you all a Merry Christmas and a Happy New Year - see
'New Years' card
Klaus
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January 2002 Volume 20 Number 1 pp 3 - 4
Doubts linger over Mexican corn analysis
John Hodgson
Research at the International Maize and Wheat Improvement Center
(CIMMYT; El Batan, Mexico) has cast some doubt on controversial earlier reports
that DNA from genetically modified maize has been transferred to local varieties
in Mexico. Although the earlier work describes the apparently widespread
occurrence of the 35S promoter from cauliflower mosaic virus in locally
developed maize varieties, the CIMMYT study could not detect the 35S promoter,
either in historical accessions from its extensive seedbank or in samples
collected recently from the field in Mexico.
The CIMMYT findings appear to be at odds both with work from Mexican government
researchers announced in September and a study published in November 2001 in
Nature (414, 541–543). The Mexican government research, which is
supported by the National Commission of Biodiversity but which has not yet been
peer-reviewed, suggested that transgenes are present in creole maize from many
sites around Mexico. The Nature paper reported that transgenic DNA
constructs—the 35S promoter together with, in two cases, sequences from an
alcohol dehydrogenase gene—had been found in a number of creole maize
varieties in two remote mountain locations in Mexico. Subsequently, both authors
of the paper, David Quist and Ignacio Chapela of the Department of Environmental
Science, Policy, and Management at the University of California (Berkeley, CA),
were reported widely in the general media, drawing attention to "risks to
food security" and threats to "the genetic bank account of
diversity." Environmentalist groups such as Greenpeace and Friends of the
Earth took up and amplified the cry, producing calls for moratoria or outright
bans on GM crops. They are particularly concerned because Mexico, as the place
where the first maize farmers dwelt, is the center of genetic diversity of the
crop.
CIMMYT's research was in part a defensive move. The center maintains an
extensive maize seedbank and supplies seeds on demand to research institutions
and extension services around the developing world. "We needed to be able
to reassure our users that transgenes were not running rampant through the
seedbank," says David Hoisington, director of CIMMYT's Applied
Biotechnology Center, "and we have shown that." Their initial results,
reported in mid-October (http://www.cimmyt.org/whatiscimmyt/init_test.htm),
could not find the 35S promoter in any of 28 maize populations in its seedbank.
They looked at 30 plants from each population. In a second phase, the CIMMYT
researchers are looking for herbicide-resistance transgenes and, importantly,
have started to examine materials that have been collected recently (1999 and
2001) from farmers' fields in Oaxaca, the state where Quist and Chapela
collected their materials.
Those studies conflict with some unreported work by the Berkeley group: the
Berkeley researchers used a CIMMYT maize sample gathered in 1971 from Oaxaca as
a negative control in their experiments. The Nature paper reports that
the original 1971 material was free of the cauliflower mosaic virus promoter
but, according to Chapela, seeds grown from that original material in the mid-
to late 1990s were not: "When we looked at later regenerations of the same
material, we picked up CMV."
One way to start resolving the conflicts would be for the various groups to
share samples. CIMMYT's recommendation to the Mexican government, for instance,
has been that they have several different and independent laboratories perform a
parallel analysis of the samples. "If they all see the same thing,"
says David Hoisington, "then you can be more sure that there is really
something there. He points out that the sensitive nested PCR technique used by
the Berkeley researchers is prone to false positives. Thus far, however, the
exchanges between the research groups have been frosty. Tim Reeves,
director-general of CIMMYT, faxed a letter to Ignacio Chapela on November 16
suggesting an exchange of experimental materials and has so far received no
response. Chapela says he is willing to allow others to use his material but
maintains that he has not received the CIMMYT request. He has, though, he says,
received a letter from CIMMYT that in effect accuses him of stealing the
material that he used as the negative control.
Meanwhile, the agbiotech community is astounded that a leading journal such as
Nature published a study containing no new information. "The paper
shows, in essence, that genes move around in nature, and this is hardly
new," says Vivian Moses, chair of the CropGen Panel, an agbio
industry–funded information initiative. Val Giddings, the agricultural
biotechnology spokesperson for the US industry organization, BIO (Washington,
DC), also believes the paper's finding were obvious: "Should we be shocked
to discover gambling in a casino?" he says.
It is not just industry representatives who believe that the Berkeley findings
are unsurprising. "Maize is an outcrossing species," says CIMMYT's
Reeves, "and the farmers' varieties today are not the same as they were two
years ago, let alone a hundred or a thousand years ago." Extensive work at
CIMMYT has shown that the creole maize varieties planted by small farmers in
Mexico are constantly changing, both as a result of the biology of the plant and
traditional practices of the farmers. In areas such as Oaxaca, which is at the
center of maize diversity, a land race is not stable, uniform, or distinct like
a plant variety. CIMMYT's sociological studies have shown that farmers
deliberately use external sources of seed to maintain vigor. "Gene flow is
constant," says Reeves, "and the real question is whether it makes any
difference if one of the genes that has flowed in is a transgene."
This is the major point of divergence in the current discussion. The Berkeley
researchers have claimed that appearance of DNA from GM crops into creole maize
compromises biodiversity. "If the transgene makes the carrier any more
fit," says Chapela, "you would expect to see the crowding out of land
races that do not carry the trait." He maintains not only that herbicide
and insect resistance can increase fitness, but also that there is some evidence
that DNA from transgenic plants is itself particularly promiscuous. "It is
the loss of diversity that is of concern," he says, "rather than the
appearance of any particular trait.
Luis Herrera Estrella, Director of CINVESTAV-IPN (Irapuato), Mexico's leading
center for plant biotechnology, has pointed out that the Nature paper
provides no experimental evidence of negative effects on biodiversity. To assess
any threat to biodiversity, the researchers would have had to identify the
phenotype of the maize they collected, something they did not do. He, too,
argues that the presence of one or two new genes in the creole maize varieties
would be unlikely to cause their disappearance.
Val Giddings agrees: "The most likely traits, if the material comes from
commercial GM maize, would be herbicide tolerance and insect resistance. What
would be the likely selective fate of those in the land races? At worst, the
impact would be likely to be neutral. It's hard to see how protection against a
pest would be negative, while herbicide resistance traits could only be neutral,
in the absence of the herbicide."
"We know what threatens biodiversity," says Giddings, "and it is
not the substitution of one variety for another in an agricultural field. It is
the conversion of native and wild land to agriculture in the first place."
He argues, therefore, that given its demonstrable influence in improving yields,
improving agronomic performance and decreasing agricultural footprints, that
biotechnology is combating the threat to biodiversity—"precisely 180
degrees around from what Quist and Chapela have proposed."
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