|
|||||
 |
 |
 |
 |
 |
 |
 |
 |
|
|
|
|
Engineered Genes Help Wild Weeds Thrive By Cat Lazaroff WASHINGTON, DC, August 9, 2002 (ENS) - For the first time, researchers have demonstrated that foreign genes from a genetically engineered crop plant can migrate into wild plants in a natural environment. A study released Thursday shows that wild weeds can incorporate bioengineered genes, potentially making the weeds stronger and more resistant to pests. Scientists from three universities studied genetically engineered sunflowers - those modified with a gene that produces a chemical toxic to certain insects - to see what happened when these foreign genes, called transgenes, were inadvertently passed along to weedy relatives.
An experimental field of wild sunflowers in Nebraska thrives after crossbreeding with Bt sunflowers. (All photos by Allison Snow, courtesy Ohio State University)"This is the first example of what might happen if a beneficial transgene accidentally spread to a wild population and then proliferated in subsequent generations," said Allison Snow, a study co-author and a professor of evolution, ecology and organismal biology at Ohio State University.The team studied hybrid sunflowers containing a transgene from the soil dwelling bacterium Bacillus thuringiensis that produces chemicals toxic to certain insects. The Bt toxin gene has been added to a number of commercial crops, including corn, cotton and soybeans, to help the plants repel moths and butterflies, whose larvae are prime predators of growing crops. The researchers crossbred cultivated sunflowers containing the Bt transgene with wild, non-Bt sunflowers. The experimental populations were grown at two sites - an open, pasture like area in Nebraska and an intensely cultivated area in Colorado. The second generation of wild sunflowers contained the transgene, showing that the alien gene could be transferred. The researchers then concentrated on learning what effects the new gene would have on the wild sunflowers. The wild Bt sunflowers had 50 percent more seeds than control hybrids without the gene. These plants also had far less insect damage, suggesting that that the insecticidal gene was working by preventing insects from eating the plant.
Sunflowers containing the gene for the Bacillus thuringiensis (Bt) toxin produced 50 percent more seeds than plants without the gene."We were surprised that a single transgene could have such a big effect on seed production," Snow said. "A plant with a transgene may have to divert more energy to handle this new compound it's making. Doing so could reduce the plant's ability to reproduce. But that certainly wasn't the case here."The researchers also found that the addition of the Bt gene did not harm the weeds' physical fitness, even when the sunflowers were deprived of water and nutrients to mimic drought conditions. "There were no costs at all to inheriting the transgene," Snow said. In many crop species grown commercially in the U.S., wild relatives will readily crossbreed with crops growing nearby. Such unions happen in more than 20 species in the United States, including sunflowers, sorghum, carrots, radishes, rice and turf grasses. Most of these crops have not yet been modified to carry insect fighting transgenes in their DNA. But as more crops are modified to resist pests, the risk that the alien genes will end up in the environment is growing.
Allison Snow, coauthor of the study."Many genetically modified cultivated crops could potentially crossbreed with weeds," Snow said. "Weeds are already hardy plants; the addition of transgenes could just make them tougher."One possible outcome of the Bt gene transfer would be a population of "super weeds," able to resist insect damage more readily than unaltered varieties. In other cases, exposure to engineered genes could make weeds resistant to herbicides used to control weed growth around crops. Certain crops, particularly soybeans, have been engineered to resist certain herbicides, allowing farmers to spray both crops and weeds while killing only the weeds. If some of the weeds were to take up this gene, they could also develop resistance to herbicides. Bt sunflowers are not currently sold in the United States. In the current study, to keep the hybrid sunflowers from spreading outside of the area of the field experiments, the researchers removed all of the non-sterile plants that carried the Bt gene. The researchers also collected seed heads from all of the remaining Bt sunflowers before the seeds had a chance to fall to the ground.
Wild sunflowers in Colorado grew more robust after adopting the Bt gene.During the two years following the study, the experimental plots and surrounding areas were sprayed with herbicides meant to kill wild sunflower seedlings."While it's obvious that a single gene can have a huge impact on plant reproduction in a natural setting, there are still a lot of unknown effects, like whether or not the weed could spread at a faster rate," noted Snow. She and her colleagues are continuing their research and trying to understand if wild sunflowers with beneficial transgenes could become troublesome weeds. Snow conducted the study with researchers from the University of Nebraska and Indiana University. The team presented their findings August 8 at the annual meeting of the Ecological Society of America in Tucson. The research was supported by the U.S. Department of Agriculture and seed manufacturers Pioneer Hi-Bred and Mycogen Seeds. |
