Tougher Weeds? Borrowed gene helps wild sunflower

Tests of sunflowers show for the first time that a gene from a genetically engineered crop gives a wild, weedy relative an edge in life outdoors, say researchers. That extra toughness feeds worries that genes escaping from transgenic crops could create feistier weeds.

Thanks to a gene borrowed from the Bacillus thuringiensis bacterium, the sunflower variety used in the test makes built-in Bt pesticide. When researchers crossed these souped-up plants with wild sunflowers, the Bt gene passed to some of the offspring, report Allison Snow of Ohio State University in Columbus and her colleagues.

To mimic the effect of a manipulated gene escaping into the wild, the scientists then crossed the first generation of transgenic hybrids with wild plants. The offspring of this mating performed well outdoors, setting extra seeds and reducing pests, the researchers reported in Tucson last week at the annual meeting of the Ecological Society of America.

Earlier research had already shown that genes can readily leak out of crops into wild plants, according to Neal Stewart of the University of Tennessee in Knoxville, who studies canola. “The genes are going to move,” he says. “What people haven’t done is look at the consequences.”

Another investigator of wandering transgenes, Norman Ellstrand of the University of California, Riverside, agrees that “we know very little about the performance of [transgenic] hybrids in the field.” He calls the sunflower work “significant and important.”

The specter of escaping transgenes haunts some crops more than others. Corn and soybeans, for example, don’t have close relatives near U.S. fields, but the Snow team points out worrisome neighbors for some 20 other crops, including rice, sorghum, canola, strawberries, and turf grasses. The sunflowers look especially prone to gene swapping since botanists consider the crop varieties and a wild weed, Helianthus annuus, to be the same species.

Ellstrand cautions that a transgene won’t necessarily help a weed. The wild plant may already have enough defenses against pests, for example, or the gene may exact a metabolic cost.

So far, no transgenic sunflowers have hit the U.S. market. Snow and her colleagues worked with an experimental variety and its wild relatives. Following strict containment procedures, the researchers planted their selected second-generation hybrids outdoors.

In a high-pest zone in Nebraska, sunflowers carrying the borrowed Bt gene set 55 percent more seeds than hybrid descendants without the gene did. Even in the less-insect-infested site in Colorado, the transgenic hybrids beat the others by 14 percent in seed setting. Also, the Bt-producing offspring suffered fewer attacks from insects.

In the greenhouse, there was no evidence that the transgenic descendants paid a price for the Bt advantage, even under drought or low-nutrient regimens, say the researchers.

The project shows that the transgene adds an edge, says Ellstrand, but now he asks whether that advantage will boost the weed’s invasion power.