Here's a more accurate article about the just published research on Mexican maize contamination.

It is also clear from this how much more circumspect Allison Snow and her co-authors are in their statements in the actual published article than Allison Snow is in her University of Ohio press release.
http://www.newswise.com/articles/view/513572/

Snow's press release, which was headlined "Genetically modified maize not found in southern Mexico", stated that, "Contrary to what many scientists thought, genetically modified (GM) corn has not yet spread to native maize crops in southern Mexico." But the published paper only says, "We conclude that transgenic maize seeds were absent or extremely rare in the sampled field(s)" !

In all, Snow et al's research looked at the pooled seeds of 870 cobs from 125 fields. This clearly could not provide a basis for claiming evidence of absence of GM genes all the many maize cobs in all the many maize fields to be found in the whole of southern Mexico!

This article similarly tells us "Snow's team points out that 'evidence that genes are rare or absent in the sampled area should not be extrapolated to other regions of Mexico without quantitative data, nor is the current situation likely to remain static'". Contrast this with Snow's statement in the University of Ohio press release that her research will be a source of reassurance to "Mexican farmers who don't want transgenes in their crops".
http://www.newswise.com/articles/view/513572/

Note too that this article directly contradicts the claim made in today's Daily Telegraph that Mexican government scientists were unable to replicate Quist and Chapela's findings of contamination of native Mexican maize: "The following year, the Mexican government confirmed that genes from GM plants had indeed contaminated wild varieties."

So what's happened since?

As Ignacio Chapela comments in the article below, "It is very difficult to believe that the contamination we found in 2001 had gone by 2003-2004. I don't believe that is something that happens in biology - ever."
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'No evidence' GM genes are still in local Mexican maize
Luisa Massarani
SciDev.Net, 9 August 2005
http://www.scidev.net/news/index.cfm?fuseaction=readnews&itemid=2279&language=1

Research published today (9 August) says that there is no evidence to support controversial claims made in 2001 that genetically modified (GM) maize had 'contaminated' local varieties of the crop in Mexico.

In 2001, Nature published research showing that genes from GM maize had entered wild maize in the Mexican state of Oaxaca despite the country not allowing GM maize to be grown at the time (see GM maize found contaminating wild strains).
http://www.scidev.net/News/index.cfm?fuseaction=readnews&itemid=61&language=1

Although the journal later disowned the paper, its authors, David Quist and Ignacio Chapela of the University of California at Berkeley, stood by their claim that one per cent of wild maize cobs contained genes from GM crops (see Nature backtracks over GM maize controversy).
http://www.scidev.net/news/index.cfm?fuseaction=readnews&itemid=2279&language=1

The following year, the Mexican government confirmed that genes from GM plants had indeed contaminated wild varieties. (see Mexico confirms GM maize contamination).
http://www.scidev.net/News/index.cfm?fuseaction=readnews&itemid=145&language=1

But in the first peer-reviewed follow-up to Quist and Chapela's study, researchers say that they found no evidence of genes from GM maize in more than 150,000 seeds taken from 870 plants in Oaxaca in 2003 and 2004.

The authors, led by Allison Snow of Ohio State University, United States, sampled seeds from 125 fields in Oaxaca.

"We conclude that transgenic maize seeds were absent or extremely rare in the sampled field," they write in today's online edition of the Proceedings of the National Academy of Sciences.

One of Snow's co-authors is Exequiel Ezcurra, of Mexico's Environment and Natural Resources Secretariat. In 2002, Ezcurra told the Mexican newspaper La Reforma that "genetic contamination of wild Mexican varieties is taking place".

At the time it was thought that GM maize imported from the United States and planted in Mexico without authorisation was the source of the genes.

Fears arose that this 'contamination' would threaten the genetic diversity of wild maize varieties, for which Mexico is the origin and centre of diversity.

Snow and colleagues (including Ezcurra) now write, however, that their results "suggest that many concerns about unwanted or unknown effects of this process can be discounted at present, at least within the sampled region".

They accept that GM genes might have been present in 2001 but say they might have since disappeared.

Chapela says he welcomes the research but says it raises more questions than it gives answers.

"It is very difficult to believe that the contamination we found in 2001 had gone by 2003-2004," he told SciDev.Net. "I don't believe that is something that happens in biology - ever."

Snow's team points out that "evidence that genes are rare or absent in the sampled area should not be extrapolated to other regions of Mexico without quantitative data, nor is the current situation likely to remain static".

Reference: Proceedings of the National Academy of Sciences doi:10.1073/pnas.0503356102 (2005)