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Black-grass and rye-grass are both widespread and serious weed problems in cereal and oilseed rape rotations. Control using weed killers is becoming increasingly problematic, with an estimated 1.2 million ha of UK land now infested with black-grass. Both black-grass and rye-grass can acquire a single defence mechanism that confers resistance to all weed killers, whatever their mode of action (MHR).

The genetics of MHR has been little understood until now. But in recently published research¹, the scientists have shown that a gene producing an enzyme called glutathione transferase (GST) is responsible for switching on MHR. When the gene was transferred to thale cress, the transgenic plants became resistant. “GSTs are known to detoxify herbicides directly,” explains project leader Professor Rob Edwards of the Centre for Novel Agricultural Products at the University of York, "but we believe that our gene works as a master switch that activates a wide range of protective mechanisms."

When sprayed with a GST- inhibiting chemical, resistant plants became susceptible to weed killers. Although the compound used in these experiments is not suitable for use as an agrochemical, this experiment demonstrates the potential of GST inhibitors to improve the effectiveness of weed killers against resistant black-grass and rye-grass.

Professor Edwards believes this to be an important development. "These weeds have developed resistance to every type of herbicide available to farmers and the problem is getting worse", he explains. "We have identified a group of compounds that could be applied along with existing weed-killers to restore the effective weed control we are currently losing”. Professor Edwards' team are also developing a genetic test for AmGSTF1 that could provide the first reliable diagnosis of MHR, an important step in deciding on the right weed control strategy.

This work was supported by joint funding from the United Kingdom's Biotechnology and Biological Sciences Research Council and by Syngenta. Dr Edwards will be talking about it at CropWorld 2013