Modified crop breeds toxic hybrid

November 27, 2002

CROSSES between genetically modified oilseed rape and a wild relative produce hybrid plants that are as toxic to insects as the original crop. Though it is still unclear how such hybrids would fare in the wild, the finding is likely to be seized on by environmentalists as proof that field trials of GM crops are unsafe.

In lab experiments, Matthew Halfhill at the University of North Carolina in Greensboro and colleagues took oilseed rape (canola) that had been modified to contain the insect resistance gene Bt and crossed it with a related weed, birdseed rape (Brassica rapa). They made 11 crosses using different combinations of plant lines. Five of them produced stable hybrids containing the Bt gene. These expressed the insecticide produced by the gene at levels similar to the GM parent and were highly toxic to insects.

The finding will fuel fears that "superweeds" containing foreign genes making them immune to insect attack might spread rapidly. But no one yet knows how much of an edge insect resistance would give the hybrids compared with their non-GM relatives. "Without doing ecological experiments, your guess is as good as mine," says Brian Johnson, biotechnology adviser to the government conservation agency English Nature.

Some researchers believe that birdseed rape may be restricted more by competition with other plants than by insects. One reason Bt-oilseed rape is not grown commercially, even in countries that allow GM crops, is that insect pests don't have a serious impact on oilseed rape. If insect resistance doesn't confer a significant advantage to birdseed rape either, the Bt gene would be unlikely to spread.

Halfhill's team also showed that similar hybrids can form under field conditions. Crosses between oilseed rape and birdseed rape are well documented, but this is the first evidence that the Bt gene might pass to the hybrid from modified crops. "This demonstrates that hybrids can and will be formed and that they will have insecticidal activity," says Johnson. He says this underlines the importance of investigating the environmental consequences before GM rape is released.
Author: James Randerson

New Scientist issue: 30th November 2002


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