The devil we don't know

日期:2018-01-16 02:33:50 作者:诸厶 阅读:

By Andy Coghlan THEY could cause an environmental disaster—or have no effect at all. It is almost impossible to predict the impact of crops genetically engineered to resist plant viruses, warns an adviser to the British government. “Viruses are, in ecological terms, something of a black box,” says Alan Gray, director of the Institute of Terrestrial Ecology’s Furzebrook Research Station near Wareham, Dorset, and a member of the Advisory Committee on Releases to the Environment (ACRE). Because ecologists know so little about the role of viruses in restricting weed populations, he says, it is almost impossible to predict what will happen if genes for viral resistance spread from engineered crops to their wild relatives. Gray presented unpublished results at the BA meeting revealing how little we know about the susceptibility of wild plants to naturally occurring viruses. He studied wild cabbages (Brassica oleracea) and wild mustard (B. nigra) on clifftops in Dorset. Gray found the plants were infected with four different viruses. What surprised him was the wildly fluctuating distribution of the viruses in both species. Some carried only one virus while their nearest neighbours had all four. Gray then exposed lab-grown wild cabbages to viruses taken from apparently healthy clifftop plants. Sixteen per cent of the plants exposed to turnip yellow mosaic virus died, compared with 6 per cent of the unexposed controls and 4 per cent treated with a second virus, turnip mosaic virus. The plants infected with the turnip yellow mosaic virus also produced fewer seeds. Gray has few clues as to why the natural distribution of viruses should fluctuate so wildly. And while his transmission experiments suggest that viruses may keep weed populations in check, much more work will be needed to understand how this works in the field. “We’re very ignorant,” says Gray, who argues that risk assessments for plants carrying genes for viral resistance should be much more thorough than those for other engineered crops. So far, ACRE has received only applications for trials of potatoes containing resistance genes. These were given the go-ahead because potatoes have no wild relatives in Britain. But virus-resistant plants with wild relatives should be much more closely scrutinised, Gray says. Oilseed rape or canola, for example, has a weedy relative in the wild turnip (Brassica rapa), which appears to readily crossbreed with engineered oilseed rape. In the US, squash plants (Cucurbita pepo) engineered to resist two viruses have already been approved for sale, though not without a prolonged fight over the risks they may pose. Groups opposed to engineered crops, such as the Environmental Defense Fund, feared that the genes could spread to wild gourds (C. texana), which are native to Texas,