Just like their traditionally bred counterparts, transgenic crops have definitively been shown to crossbreed with crops or native plants growing nearby.
In the July-September issue of the University of California's California Agriculture journal, a peer-reviewed review article documents widespread evidence that crop transgenes do, in fact, wander in the environment.
But is this a cause for worry?
"The products of traditional plant improvement are not absolutely safe, and we cannot expect transgenic crops to be absolutely safe either," writes Norman C. Ellstrand, director of the Biotechnology Impacts Center and genetics professor at UC Riverside. "The creators of transgenic plants need to be as mindful of possible problems with their products as they are of potential promise."
With this issue, California Agriculture launches a special series on the risks and benefits of agricultural biotechnology. Three peer-reviewed research articles focus on transgenic crops, fish and animals. (Future issues will examine transgenic insects, pharmaceutical crops and other concerns.)
Transgenic plants are engineered with genes from other plants or organisms to express agronomically desirable traits, such as herbicide or insect resistance, or higher vitamin levels. In 2005, the world's billionth acre of transgenic crops was planted; most of that acreage was in the United States, primarily in corn, soybeans and cotton.
Ellstrand, author of the 2003 book Dangerous Liaisons? When Cultivated Plants Mate With Their Wild Relatives (Johns Hopkins Press), has conducted extensive research on gene transfer among plants, in addition to field studies.
For example, Ellstrand and colleagues showed that one of the world's most important crops, sorghum, spontaneously hybridized with one of the world's worst weeds, johnsongrass, even when they were grown up to 330 feet apart; furthermore, the two plants are distinct species with different numbers of chromosomes. Other labs have demonstrated crop-to-wild gene flow with sunflower, rice, canola and pearl millet.
Transgenic crops are no different. Transgenic canola has crossbred with its native relative, creating herbicide-resistant volunteers. A more well-known example is transgenic Starlink corn, which was not approved for human consumption but appeared in a variety of corn-based foods. "For a decade, more than a dozen cases of transgenes and/or their products out-of-place have been reported," Ellstrand notes in California Agriculture.
In two other peer-reviewed articles in California Agriculture, Alison L. Van Eenennaam, UC Davis animal genomics and biotechnology specialist, examines environmental and public-policy concerns related to transgenic fish and mammals.
To date, just one transgenic fish has been approved for sale in the United States, a red-fluorescent zebra danio for aquariums (California has banned the fish). A growth-enhanced salmon is currently under federal review. Risk factors associated with transgenic fish include unintended release or escape, and related ecosystem imbalances. For example, in one study "fast-growing transgenic salmon were found to dominate feed acquisition and exhibit strong agonistic and cannibalistic behavior toward their [nontransgenic] cohorts when there were inadequate feed resources," Van Eenennaam writes.
However, Van Eenennaam notes that "neither the risks nor the benefits of transgenic fish are certain or universal." Rather, they vary according to a variety of factors. "Regulators need to apply a scientifically sound, risk-based framework to assess the ecological risks involved with each transgene, species and receiving ecosystem combination on a case-by-case basis."
No genetically engineered food animals have been approved for global or U.S. sale, although numerous animal species have been cloned (but not sold for food) and transgenic animals are producing commercial, nonfood items such as spider silk (by goats). Van Eenennaam notes that transgenic animals raise unique ethical concerns due to "the special place that animals hold in our society."
This concern is often at odds with the scientific process, which "places a high value on controlled experiments as a way to obtain understanding," Van Eenennam writes. She urges scientists to pursue effective and responsible communication with all stakeholders, in order to "reach a consensus on the acceptable levels of risk for specific products of animal biotechnology, and to determine which set of values will ultimately be applied to decide the acceptable uses of animal biotechnology."
California Agriculture is the University of California's peer-reviewed journal of research in agricultural, human and natural resources. The full articles are posted online at http://californiaagriculture.ucop.edu
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