The case

November 29, 2001, the scientific journal Nature reported "the presence of introgressed transgenic DNA constructs in native maize landraces grown in remote mountains in Oaxaca, Mexico" (Quist & Chapela, Nature 414: 541-543). The paper attracted a lot of attention, particularly because Oaxaca is located in the primary centre of diversity of maize and its wild ancestor, teosinte. The substantial genetic diversity in this Mexican region is a major source for maize breeding. The results were taken to indicate that transgenes may have spread and that this will influence the genetic composition of these valuable genetic resources.

Quist and Chapela, scientists of the University of California, Berkeley, sampled maize cobs of landraces from four fields in two locations. They found pieces of DNA constructs that are currently used in commercially grown transgenic maize in the USA. They concluded that their results "demonstrate that there is a high level of gene flow from industrially produced maize towards populations of progenitor landraces". These results are unexpected, given a moratorium in Mexico on the planting of transgenic maize since 1998. It is not known how the transgenes were introduced into the local maize populations. Quist however suggests that the transgenes are likely to originate from US-grown seed previously provided as food aid in the region to compensate for low crop yields.

The debate

According to the NGO ETCgroup (formerly RAFI) and a coalition of other NGOs, the transgenes would lead to loss of an essential source of biodiversity. Local farmers were reported to be worried about the health of their children (Newsweek, 28.01.2002), and it was claimed that gene banks in the region are contaminated, in particular the genebank of CIMMYT, maintaining the world's most important maize collection. Environmentalists demand far-reaching actions such as a global moratorium on transgenic crops in general ( ETCgroup and Food First in various reports). The Nature publication also generated severe criticism from other scientists. Christou, editor-in-chief of 'Transgenic Research', concluded on behalf of the full editorial board of this scientific journal that "no credible scientific evidence is presented in the paper to support claims made by the authors that gene flow . . . . has taken place" (Transgenic Research 11: iii-v, 2002) This view was supported in the journal Nature Biotechnology. The findings of Quist and Chapela were attributed to laboratory artefacts resulting from DNA contamination combined with the polymerase chain reaction (PCR) technology used in the laboratory. An independent, secondary technology to confirm the results is considered to be the minimal requirement for valid scientific conclusions about the actual occurrence of gene flow to the maize landraces.

Analysis: impact on biodiversity

We acknowledge and agree with the possibility of experimental artefacts in the Quist&Chapela experiments. However, the case has sparked a much wider and very relevant discussion. We consider it not interesting to know whether gene flow actually occurred in the particular case described, as it is generally spoken likely to occur when modern varieties (conventional or transgenic), and landraces or wild relatives do grow in close proximity. This spread - scientifically referred to as 'introgression' - will be as likely for any maize genes from modern varieties or hybrids as for transgenes now present in commercial maize.

In our opinion, there will be no automatic loss of maize biodiversity as a consequence of the introgression of the transgenes currently used in commercialised maize in its centre of origin. It is highly unlikely that these transgenes will give sufficient selective advantage to outcompete the plant material already present in such centres of origin. No original plant material will disappear at all, since the 'new' genes will evenly spread in the diverse populations through natural cross breeding (in effect a random introgression process). This plant material will therefore remain available for further breeding and other uses.
In the current case the reports show that none of the gene constructs allegedly found were active, the maize did not exhibit the traits involved, confirming an absence in selective advantage and thus no threat to biodiversity in the local maize population (for details see CIMMYT's David Hoisington in Newsweek, January 28th).

It should, however, be pointed out clearly that genetic diversity in maize in this important centre of diversity is indeed threatened. This is not due to potential introgression of current generation transgenes but to the spread of modern agriculture in Mexico, based on genetically narrow populations of uniform hybrids, limiting the active maintenance and use of traditional and potentially valuable local landraces to remote and more marginal areas. These landraces are used in dynamic systems of seed selection, exchange and local improvement. Farmers are continually looking for and test new diversity to improve their yield levels, yield stability and product quality. Samples from neighbouring landraces and modern varieties (e.g. through migrant workers) are regularly intentionally introduced and hybridised for this reason (see Louette, 2001 in Brush: 'Genes in the Field'). Also, food-aid grains are commonly used as a source of 'new' diversity. In a letter to the editor of Nature Biotechnology (January 2002) four Mexican researchers claim that Mexican farmers would incorporate transgenes to enrich their maize when these traits would prove beneficial for their crop. Again, such steps would not necessarily reduce genetic diversity in their landraces.

The likelihood of introgression of maize genes into the wild ancestor of the crop, teosinte, is very limited due to a different reproduction biology and reproduction time. Teosinte grows as a weed in maize fields. By observation, it remains uneffected and clearly identifiable: the transgenes can not be expected to easily introgress into the teosinte populations, and therefore are not likely to effect the biodiversity of the wild ancestor of maize. In conclusion, maize genetic diversity is threatened by the spread of modern varieties. A transgenic introgression does not essentially influence this trend.

Transgenes in genebank stocks

Claims that genebanks, the repositories of genetic resources, contain transgenes, cannot be substantiated. It is highly unlikely that transgenes are currently (unintentionally) present in genebank collections. Introduction of transgenes in genebank accesions could occur in only two ways:
i) through uptake of new accessions,
ii) through introgression during multiplication/regeneration of samples.

The former case presents itself when transgenes have entered local populations as in the Quist&Chapela claim. This will thus be restricted to recent acquisitions by genebanks. The latter case is unlikely in view of the management practise of genebanks. Multiplication of samples by genebanks is always done with the aim to prevent introgression from any source. Even if there would be low frequencies of transgenes in samples, a DNA analysis on parents in a breeding programme would suffice to exclude any transgene-containing individual and to rule out any unintentional or undesired use of transgenes in subsequent breeding. The putative presence of transgenes in genebank stocks is therefore neither uncontrollable nor irreversable.

Further analysis: a myriad of other aspects

Numerous additional issues have to be taken into account when analysing the potential impact of the introgresssion of transgenes of unknown origin into local and genetically diverse populations of crop plants
· Philosophical/ethical considerations: genes from foreign species may be regarded by some stakeholders as a serious threat to what is seen as the species integrity of the crop.
· Food safety aspects: when transgenes have not been tested for food safety impact, or when they are released for the use in animal feed only (ref: Starlink maize), an introgression into local crops by (uneducated) farmers is undesirable . This is however not an issue in the reported case.
· Trade aspects: where farmers intend to sell their product at premium prices in certified non-GMO markets, unintended introgression of transgenes may pose a threat to their commercial position. That is probably not yet the case in these remote areas of Oxoaca. For comparison, we refer to the debate in Europe on the conditions to guarantee GMO-free food chains.
· Intellectual property right issues : introgression of patented genes may sooner or later result in claims by the patent holder, even where farmers introduced the genes unintentionally. It is unlikely that patent holders will file claims against small-scale farmers, but recent court cases in Canada (Monsanto vs. Schmeiser) show that the IPR issue warrants attention in general.

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