Modified Crops Could Lead to "Superweeds," Study Suggests

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Nonetheless, the scientists found that traits acquired from the crop radishes, such as their flower color, showed up in subsequent generations of hybrids.

"Even though the effects of delayed flowering and reduced fertility inhibited the movement of certain crop traits to later generations, we did find evidence of crop genes in every generation," Snow said.

A second experiment, conducted in field plots, supported these findings and will be published soon.

Need for Caution

The results of the experiments challenge a common belief that hybrids gradually die out over several generations, Snow explained. "There has been an assumption that [crop] genes wouldn't persist in crop-weed hybrids" because hybrids are thought to be less successful at reproducing, she said.

Not so, Snow concluded after reviewing her team's data: Hybrid wild radishes survived in all six generations that were grown since the study began.

Although the genetic traits the scientists monitored were natural and not genetically engineered, the findings nonetheless suggest that artificial improvements introduced into crops through genetic engineering could spread to weeds and become permanent traits of the weed population.

So strengthened, the weeds may pose a serious risk to the long-term health of agricultural crops. The danger exists in a number of crop plants—including canola, rice, sunflower, sorghum, squash, and carrots—that are closely related to weeds with which they compete.

Snow is concerned that the transfer of genes from crops to related weeds could rapidly render many herbicides ineffectual. That situation, she said, would be much like bacterial diseases acquiring resistance to antibiotics.

Because plant hybrids arise in a single generation, however, it could happen much more quickly.

"Modern agriculture is heavily dependent on herbicides," she said, "so people will notice when those don't work anymore."

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