Amy Coombs - Revenge of the Weeds
May 23, 2012 It’s a story suited for a Hollywood horror film, yet it’s also a tenet of evolutionary biology. Introduce a toxin to a system, and you inevitably select for resistant survivors. These few individuals gain a reproductive advantage and multiply; sometimes they can’t be stopped with even the most potent chemicals.
For years, this general plot line made headlines in the fields of antibiotic resistance and cancer research. More recently, plants have become a common protagonist. Weeds around the world are developing resistance to glyphosate—one of the most common herbicides on the market—and like bacteria and tumor cells, many plants can also withstand multiple other toxins, each with unique molecular targets.
In January, a hair-raising infestation of the kochia shrub was confirmed in Alberta, Canada. Originally introduced to desert climates as forage for cattle, the tenacious weed can now survive glyphosate, which targets an enzyme involved in the biosynthesis of aromatic compounds. It can also withstand chemicals that inhibit the ALS enzyme, involved in the production of amino acids. At least 2,000 acres are now impacted, and “we expect more cases will be confirmed after a field survey this fall,” says Hugh Beckie of Agriculture and Agri-Food Canada, the government department that manages farming policies.
The United States are also being taken by storm. Palmer amaranth recently developed resistance to the same two classes of chemicals in Tennessee. Since 2009, the tall, spindly weed has swept across 1 million acres of cropland, causing some farmers to abandon their fields. And in California, a plant named hairy fleabane recently crept into vineyards. It is now able to withstand both glyphosate and Paraquat—a chemical that hijacks photons from proteins involved in photosynthesis.
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