Spread of GM maize in Mexico

"GM maize" disappeared – Questions still remain

Genetically modified maize is apparently no longer growing in Mexico. This is the surprising finding of a study by a six-strong team of researchers from Mexico and the USA.

A few years earlier, scientists found traces of GM maize in native Mexican maize varieties, sparking a heated debate. It was felt that the genetic diversity of native maize plants was under threat. Mexico is regarded as the birthplace of maize: nowhere else in the world are so many local variants of this plant to be found.

Maize Diversity. Mexico is regarded as the birthplace of cultivated maize. There are countless local varieties with vast genetic diversity.

In 2001 and 2002 at least three independent studies concluded that genetically modified maize had spread to Mexican maize varieties. At the time the most likely cause was thought to be small-scale farmers using maize imports from the USA with a high proportion of GM maize as seed, despite the fact that the cultivation of genetically modified plants is illegal in Mexico.

However, according to the recently published study, no further trace of transgenic material was found in samples taken in 2003 and 2004 from the mountainous region of Oaxaca.

The researchers, including Alison Snow from Ohio State University, examined seeds from 870 plants from 125 fields at 18 different locations. In total the team analysed more than 150,000 seeds from the 2003 and 2004 harvests for transgenic elements.

The researchers used standard PCR (polymerase chain reaction) methods, which can be used to identify the extra genes in genetically modified plants. They were looking for two gene sequences, at least one of which is present in all commercially grown GM maize varieties today. The samples were then analysed simultaneously by two independent research laboratories, and not a single positive result was found.

Since this type of study is based on analysing random samples, it is possible that transgenic maize kernels present in the crops may have avoided detection. The calculation of this probability by statistical analysis indicates that the proportion of genetically modified maize plants in the Oaxaca region in 2003 and 2004 was between zero and a maximum 0.4 percent.

The studies conducted in 2000/2001 in the same region seemed to conclude that up to eight percent of maize plants contained genetically modified seed. At the time, researchers David Quist and Ignacio Chapela were the first to detect transgenic elements in the maize, findings which were subsequently replicated in independent studies by the National Institute of Ecology, the National Commission for the Knowledge and Use of Biodiversity and the Interministerial Commission on Biosafety and Genetically Modified Organisms in Mexico.

Ignacio Chapela appeared very surprised by the results of the latest study. In a statement released on the Internet he announced that he would shortly be publishing a detailed response to the latest study, in which he would be outlining methodological and technical shortcomings.

Attempts to explain the conflicting results.

The authors of the current study have no wish to fundamentally challenge their colleagues’ earlier findings. If transgenic material really had found its way into native maize plants some years earlier, they could conceive of several mechanisms to explain its subsequent apparent disappearance:

On being informed of the results of the 2000/2001 studies, the Mexican government made it absolutely clear to farmers that the cultivation of genetically modified maize was illegal. As a result the supply and cultivation of further genetically modified maize plants from the USA may have stopped.
The frequency of occurrence of transgenic elements in maize can be greatly reduced by backcrossing with native maize variants (so-called landraces). Foreign genes can also dwindle randomly due to “genetic drift”, if they are only found in relatively isolated populations.
The maize imported from the USA is predominantly hybrid. Subsequent generations of these hybrid maize plants are considerably less vigorous. In addition, North American maize varieties are not adapted to the environmental conditions found in Mexico (climate, pests, pathogens). This means that the native maize plants are superior and suppress the transgenic maize.
The maize imported from the USA is predominantly hybrid. Subsequent generations of these hybrid maize plants are considerably less vigorous. In addition, North American maize varieties are not adapted to the environmental conditions found in Mexico (climate, pests, pathogens). This means that the native maize plants are superior and suppress the transgenic maize.
The incrossing of foreign genes to Mexican landraces can be detrimental to these plants. For example, if the foreign genes in the genetically modified maize are located immediately adjacent to genes which are not beneficial to the plants under Mexican growing conditions. Contiguous genes are usually transferred together and can therefore reduce the competitiveness of the plants concerned.

The scientists do not regard their results as an all-clear signal, but rather as a starting-point for further research. They recommend further monitoring studies to better assess the risks to staple food crops of a potential spread of transgenic material.

"GM maize" disappeared – Questions still remain

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