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A genetically modified (GM) variety of potato able to resist a major crop pest does not threaten other organisms, and — because the plants produce no viable pollen —  is unlikely to pass genes to related varieties, according to research published yesterday (11 November) in Nature.

The researchers, led by Howard Atkinson at the University of Leeds, UK, say their method ensures biosafety without challenging the value of the precautionary approach to the introduction of GM crops in regions where many closely related species exist. The precautionary approach could, according to the Nuffield Centre of Bioethics, prevent poor farmers and consumers in developing countries from reaping the potential benefits of modified crops.

Atkinson and colleagues in Bolivia, Peru, and The Netherlands inserted a gene from rice into potatoes to protect them from a microscopic nematode worm that causes tens of millions of dollars of damage in Andean countries by reducing crop yields.

The gene produces a protein — cystatin — that interferes with the nematode's ability to digest protein in its diet. By ensuring that the gene is only active in potato roots and not the part of the plant above ground, or the potato tuber itself, the researchers minimised its potential for interaction with non-target species.

The gene would therefore not enter the human food chain, although cystatins already occur in the human diet in rice and maize and are also present in saliva, so are considered unlikely to pose risks to human health.

By comparing the insects and microbes associated with GM potatoes, non-GM potatoes and other non-GM crops, the researchers showed that the addition of the rice gene had no more effect on non-target organisms than common agricultural practices such as choice of crop.

However, they found that pollen from GM potatoes can spread over short distances to related varieties and species, giving rise to hybrid offspring carrying modified genes. Because the gene protecting GM potatoes from nematodes might also benefit these relatives, there is a risk of such plants becoming invasive.

To overcome this problem, the researchers inserted the rice gene into a variety of potato called Revolucion. Potatoes have male and female parts in the same flower but Revolucion is 'male sterile'. It fails to produce viable pollen and cannot pollinate other potato plants or their wild relatives. This, say the researchers, "provides a basis for initial field trials of nematode resistance or other traits of value without gene flow from the potato on trial".

"This approach is practical for crops such as potato and banana that can reproduce asexually," says Atkinson.

Yesterday's paper in Nature, written by Carolina Celis of Wageningen University in The Netherlands, says that transgenic planting of potatoes in the Andes should be limited to male sterile cultivars until concerns about possible spread of genes to related species are investigated experimentally. Celis and colleagues say the findings mean there is no need to invoke the precautionary principle to bar field trials of their GM potatoes.

"We seek to carry out field trials of the technology for potato and banana in areas where no wild relatives exist, such as in China in the case of potato," Atkinson told SciDev.Net. "We would also like to test Revolucion under field conditions in the Andes in isolation from other related plants to assess the benefits and to show a lack of environmental impact on non-target organisms".

Link to full paper in Nature