Genetically Modified Crops Pass Benefits to Weeds

Herbicide resistance could confer an advantage on plants in the wild.

August 16, 2013 | Source: Nature | by Jane Qiu

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A genetic-modification technique used widely to make crops herbicide resistant has been shown to confer advantages on a weedy form of rice, even in the absence of the herbicide. The finding suggests that the effects of such modification have the potential to extend beyond farms and into the wild.

Several types of crops have been genetically modified to be resistant to glyphosate, an herbicide first marketed under the trade name Roundup. This glyphosate resistance enables farmers to wipe out most weeds from the fields without damaging their crops.

Glyphosate inhibits plant growth by blocking an enzyme known as EPSP synthase, which is involved in the production of certain amino acids and other molecules that account for as much as 35% of a plant’s mass. The genetic-modification technique – used, for instance, in the Roundup Ready crops made by the biotechnology giant Monsanto, based in St Louis, Missouri – typically involves inserting genes into a crop’s genome to boost EPSP-synthase production. The genes are usually derived from bacteria that infect plants.

The extra EPSP synthase lets the plant withstand the effects of glyphosate. Biotechnology labs have also attempted to use genes from plants rather than bacteria to boost EPSP-synthase production, in part to exploit a loophole in US law that facilitates regulatory approval of organisms carrying transgenes not derived from bacterial pests.

Few studies have tested whether transgenes such as those that confer glyphosate resistance can – once they get into weedy or wild relatives through cross-pollination – make those plants more competitive in survival and reproduction. “The traditional expectation is that any sort of transgene will confer disadvantage in the wild in the absence of selection pressure, because the extra machinery would reduce the fitness,” says Norman Ellstrand, a plant geneticist at the University of California in Riverside.