Student - February 26, 2009


Over the past few years, bits of genetic material from genetically modified (GM) maize have ended up in landraces in Mexico. This is reported in this month’s Molecular Ecology by Mexican researchers and Wageningen PhD holder Joost van Heerwaarden.

Farm workers use digging sticks to sow maize in Puebla State in Mexico.
The results of the research into what is called the gene flow in GM maize are politically sensitive because biotechnology companies and environmental organiza¬tions have been arguing for years about the risks of GMOs spreading uncontrollably. As early as 2001, Mexican researchers offered indirect evidence of the presence of transgenes in conventional maize. Using the polymerase chain reaction (PCR), they found the agrobacterium 35S, which is routinely used to introduce gene packages into GM maize. Nature magazine rejected the research on grounds of technical shortcomings, however.
In 2005, a follow-up study was published in PNAS. A government laboratory had found transgenes in samples, while two commercial laboratories found no convincing evidence. This led to a discussion about ways of using statistics.
In the new study, the researchers took new samples at the locations where transgenes were said to have appeared in landraces. They investigated these samples using not only PCR but also the technique known as southern blotting. In the Oaxaca area that had been investigated in 2001, they found transgenes in landrace at three of the 23 locations. At two of these locations, transgenes had been found in 2004 as well. A species is counted as a landrace if farmers use part of the harvest as seed for their next crop.
GM maize has been prohibited in Mexico since 1999, but it is widely available across the border in the US. The researchers guess that Mexican farmers – whether deliberately or not – imported GM seed, and that cross-pollination with local maize then took place. This also explains why the distribution of the transgenes over the maize fields is irregular.
Van Heerwaarden and his colleagues at the National University of Mexico pay a lot of attention in their article to the possible explanation for the varying results in the past. ‘If we had taken random samples in the area, we might not have found anything’, says Van Heerwaarden. Taking samples at specified locations increased the chances.
Researcher Linus Franke from Plant Research International comments that the researchers did not find the transgenes themselves, but their promoter. ‘That is not conclusive evidence of the presence of transgenes, but it is a strong indicator.’
According to his colleague Bert Lotz, the research results have no consequences for the Dutch policy, known as the co-existence policy, which regulates the co-existence of agricultural chains with and without GMOs. ‘In the Netherlands farmers use certified sowing seed and not part of the previous season’s harvest’, says Lotz. Earlier research carried out by him showed that cross-pollination between GM and conventional maize fields is less than 0.1% if co-existence agreements are observed. That is well below the limit of 0.9% above which products in the EU must be labeled as GM.