Resistant Weed Could Outdo Crop

6 August 1998 8:00 pm

BALTIMORE--Weeds that acquire genes for herbicide resistance from a genetically engineered crop can reproduce just as well as nonhybrid weeds. The finding, reported here today at the Ecological Society of America's annual meeting, suggests that scientists will have to find more sophisticated ways to engineer plants to prevent valuable traits from escaping into nearby weeds.

Spraying entire fields with herbicides is much more efficient than targeting just the weeds. To take this broad-brush approach, scientists insert herbicide-resistance genes into the DNA of crops. But when the crop plants release pollen, weedy relatives growing near the crops can take up the resistance genes through the pollen. Because cultivated crop plants are generally less robust than weeds, however, researchers have thought that any genetic mixing should result in less hardy weeds.

To test this idea, plant biologist Allison Snow of Ohio State University in Columbia and colleagues at the Risoe National Laboratory in Roskilde, Denmark, crossed a herbicide-resistant version of Brassica napus, the rapeseed plant used to make canola cooking oil, with its weedy cousin, Brassica rapa. They grew the hybrid weeds and compared them to regular weeds. Both produced similar amounts of seeds and thus could reproduce equally well. This means that crops won't have any edge in competing with weeds, says Snow.

But some experts are not convinced that resistant weeds will be a widespread problem. "There's not many crops that have weedy relatives in the U.S." that could accept the resistance genes, says Juliette Winterer, a population biologist at Franklin & Marshall College in Lancaster, Pennsylvania, although resistance may spread from carrots, squash, and sunflowers as well as rapeseed. Scientists may try to circumvent this gene transfer by inserting genes into a crop plant cell's cytoplasm, where they can only be inherited through the seeds.