BLOOMINGTON, Ind. -- As concerns rise about the ecological impacts of genetically modified crops, a new Indiana University study urges a pragmatic approach to dealing with "transgenes" that escape from crop plants into the wild. Use of transgenic crops is becoming more common as farmers reap benefits from the plants' decreased susceptibility to disease and increased marketplace value.
IU biologist Loren Rieseberg and former postdoctoral fellow John Burke (now at Vanderbilt University) reported in the May 23 issue of Science that a wheat transgene synthetically inserted into sunflowers has little or no effect on crop sunflowers' wild relatives and is not likely to impact the environment.
"We found that a certain transgene that gives crop sunflowers resistance to white mold is unlikely to spread rapidly to the wild because the transgene doesn't affect the seed-producing abilities of wild sunflowers in nature," said Rieseberg, who led the study. "We need to examine each transgene and crop on a case-by-case basis. Some transgenes will have major ecological impacts and others probably won't."
For example, another study co-authored by Rieseberg, published last month in Ecological Applications, showed that a bacterial transgene inserted into sunflowers significantly increases seed production of wild sunflowers and therefore may incur ecological costs.
A common worry about genetically modified (GM) crops is that new, highly advantageous genes will seep through wild populations as crop plants mingle and reproduce with their wild cousins.
While the new report by Rieseberg and Burke does not refute that worry, the researchers believe that the movement of certain genes from GM crops into the wild may occur at a glacial pace, meaning wild plants in locations far from their alter egos in farm crops will not encounter the transgenes for a long time.
"The question isn't whether these transgenes will escape into wild relatives -- we know they will," Rieseberg said. "Even if the wild hybrids are partially sterile or inviable, genes will still move across the farm property barrier. So it's really the fitness effects of a gene that dictate the speed at which it spreads. Genes that aren't advantageous to the wild plants will spread very slowly. The transgenes that are truly deleterious to wild species won't move much at all."
The scientists introduced a wheat gene for the white mold-combating enzyme oxalate oxidase (OxOx) to wild sunflowers and compared wild plants with and without the transgene at natural study sites in California, North Dakota and Indiana. Half of the plants in each group were inoculated with white mold. At the end of the study period, Rieseberg and Burke counted the number of seeds produced by each plant. The researchers found that the OxOx transgene had no appreciable effect on the wild plants' ability to produce seeds. Wild plants lacking the transgene made just as many seeds as plants with the transgene. Rieseberg and Burke also found that the OxOx transgene did not harm any of the sunflowers that possessed it when they were not exposed to the disease.
White mold infection has plagued sunflower farmers for years. Attempts at breeding natural resistance in the economically important plant have generally failed. Fungicides are costly and ineffective, and they may carry health consequences for consumers. The introduction of the OxOx gene to sunflower crops may help reduce their susceptibility to mold.
Both the Science and the Ecological Applications reports were funded by grants from Pioneer Hi-Bred International Inc., a DuPont Corp. company.
Source: "Fitness Effects of Transgenic Disease Resistance in Sunflowers," Science, vol. 300, no. 5623
Materials provided by Indiana University. Note: Content may be edited for style and length.
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