WHETHER or not Chapela and Quist鈥檚 work stands up to scrutiny (see main story), there鈥檚 no denying that transgenes have spread to traditional maize varieties cultivated in Mexico.
Last month, researchers told a conference in the Netherlands that two separate teams have found transgenic DNA in around 10 per cent of crop plants sampled in Oaxaca province. 鈥淚t is confirmed. There is no doubt about it,鈥� says Jorge Sober贸n of the National Biodiversity Commission in Mexico, who described it as 鈥渢he world鈥檚 worst case of GM contamination鈥�. Contrary to many reports, however, no studies have found any evidence of transgenes in wild maize.
The genes spread despite a ban on the planting of GM maize that Mexico imposed in 1998 specifically to prevent such contamination. Maize was bred from wild grasses in Mexico 6500 years ago, and a rich selection of strains is grown by small farmers. Despite the precautions, transgenic Bt maize imported from the US for food appears either to have been deliberately planted or spilt in fields, and the transgenes are now probably also spreading by cross-pollination.
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So does it matter? Some think the effect will be to wipe out diversity. GM contamination 鈥渕ay destroy the genetic integrity of the diverse varieties in these centres that are humanity鈥檚 insurance against future threats from disease, climate change and biotechnological calamities鈥�, says Patrick Mulvany of the British-based Intermediate Technology Development Group. 鈥淕overnments should declare an immediate moratorium on the release of GM crop seeds and grains in centres of crop diversity.鈥�
There is no doubt that old varieties and wild relatives of crop plants are a valuable resource for breeders. But they鈥檙e already disappearing fast, and the main threat is not GM pollution but the abandonment of traditional varieties in favour of modern hybrids.
Mexico鈥檚 problem isn鈥檛 likely to go away. Bt maize contains a gene for a bacterial toxin that kills some pests. This gives it an advantage over other strains, making it more likely to spread further even if farmers don鈥檛 knowingly choose to plant these seeds.
But this won鈥檛 necessarily spell doom, according to the International Maize and Wheat Improvement Center (CIMMYT) in Mexico. It says diversity could actually increase as a result. The Bt gene won鈥檛 wipe out other genes, but will make the overall mix that little bit richer. And if plant scientists find a desirable trait in a contaminated variety, they can easily breed plants that contain the desired trait but lack the Bt gene.
Nor does the contamination pose any particular threat to the two types of wild maize found in Mexico, teosinte and Tripsacum. Teosinte only occasionally interbreeds with cultivated varieties, while hybrids between Tripsacum and maize are even rarer.
It seems unlikely that the contamination of Mexican maize with the Bt gene will have any serious consequences. But it is deeply disturbing that extensive gene flow took place despite Mexico鈥檚 efforts to prevent it. CIMMYT warns that other kinds of genes could spell trouble. Those designed to produce industrial products such as medicines, for example, might make maize unsafe to eat, and such contamination would be very difficult to deal with. Next time it could be worse.
Such fears don鈥檛 appear to trouble the industry. 鈥淚t is better to acknowledge that a minimum of cross-pollination cannot be avoided, and not to panic,鈥� said Guy Poppy of the British biotech association CropGen, after Chapela and Quist鈥檚 paper first appeared.
There are ways of preventing genetic pollution, such as 鈥淭erminator鈥� technology (see New 杏吧原创, 28 October 2000, p 4). Perhaps now is the time to start using them.