Virus mystery

ALAN GRAY, director of the Institute of Terrestrial Ecology's Furzebrook Research Station, and a member of Advisory Committee on Releases to the Environment (ACRE), warns that it is impossible to predict how the genetically-engineered crops to resist plant viruses will behave. "Viruses are, in ecological terms, something of a black box," he said. Because ecologists know so little about the role of viruses in restricting weed populations, it is almost impossible to predict what will happen if genes of viral resistance spread from engineered crops to their wild relatives, said Gray. He has studied wild cabbages and wild mustard on clifftops and found that plants were infected with four different viruses.

What surprised him was the wildly fluctuating distribution of viruses in both species. Some carried only one virus while the nearest neighbour had all four. Gray also exposed lab-grown wild cabbages to viruses which were found in healthy clifftop plants. About 16 per cent of the plants exposed to turnip yellow mosaic virus died, compared with six per cent of those that were unexposed. Also, plants infected with the turnip yellow mosaic virus produced fewer seeds. After the study, Gray has some clue as to why natural distribution of virus should fluctuate so wildly. One significant result of the tests is that while viruses may keep weed population in check, much more work will be needed to understand how this works in the field. Gray further adds that virus-resistant plants with wild relatives should be closely scrutinised.

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