No wonder wheat and barley farmers in Europe and Australia have trouble killing ryegrass and black-grass. These plants have a master gene that makes some strains resistant to all major herbicides. “This is a general detoxification mechanism, just like the way tumours detoxify anticancer drugs,” says Robert Edwards of the University of York, UK. The good news is that if the gene can be neutralised, it would take out the weeds’ resistance at a stroke. That could be very desirable as black-grass and annual ryegrass pose a growing problem for cereal farmers. In Australia, for example, the plants can wreck entire harvests. Most forms of herbicide resistance work by sabotaging the specific target against which a weedkiller acts. But the troublesome grasses have a gene called AmGSTF1, which makes an enzyme called a glutathione transferase. This causes the plant to make lots of protective antioxidants. These chemically neutralise many toxins in much the same way that human tumours which also rely on glutathione transferases can resist many drugs. When Edwards transferred the AmGSTF1 gene from black-grass into thale cress, the cress became resistant to the herbicides. However, Edwards’s team also discovered a solution: a drug called 4-chloro-7-nitro-benzoxadiazole. It is sometimes given to people with cancers that are resistant to many drugs, because it blocks glutathione transferases. When Edwards sprayed it on the weedkiller-resistant cress, the cress became vulnerable again. Edwards says the drug is too toxic for use on farms, but benign versions could be developed to switch off resistance, enabling farmers to kill weeds. Furthermore, his team is trying to develop a test so farmers can quickly tell whether weeds have an active master gene.
New Scientist, 25 March 2013 ;http://www.newscientist.com/ ;