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Promiscuity in transgenic
by Bob Hartzler
December 21, 1998 - One risk of transgenic crops is the transfer of transgenes to native plants growing in the vicinity of the genetically altered crop. Previous research has documented movement of the glufosinate (Liberty) resistance gene from oilseed rape to a weedy relative, field mustard. The risk of gene transfer from crops to native plants has been reported to be minimal in cases where the crop is largely self-pollinating or if no weedy relatives are present where the crop is grown. However, an article in the August issue of Nature (Bergelson, J., C. B. Purrington, and Gale Wichmann. 1998. Promiscuity in transgenic plants. Nature 395:25) demonstrates that assessing these risks may not be as simple as some have stated.
Researchers at the University of Chicago investigated outcrossing from ALS-resistant Arabidopsis thaliana to a susceptible biotype of the species. This species is highly self-pollinated, and thus the risk of cross-pollination would be considered low. Two types of herbicide resistant biotypes were used: a genetic mutant created through traditional breeding techniques and a transgenic biotype in which an ALS resistance gene from a different species was inserted at a single site in the plants genome. The resitant biotypes were planted at random spots in a field infested with a wild-type A. thaliana. At the end of the growing season seed was collected from the wild type plants and the progeny were tested to determine the source of pollen responsible for pollinating these plants (native vs. mutant vs. transgenic).
Analysis of approximately 100,000 seeds found that the outcrossing rate was 0.3% for mutant plants and 6.0% for the transgenic plants. Thus, while the overall rate of outcrossing was low, the plants which had been modified for ALS-resistance through gene transfer were 20 times more likely to outcross than the non-transgenic resistant biotype.
At the time of release of this article the authors did not have an explanation why genetic transformation of A. thaliana should increase the outcrossing potential. These findings support concerns of critics of genetic engineering who have stated that we really know very little about how these types of modifications of plants (or animals) will influence their behavior once they are released into the wild.
Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University
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