Weediness And Gene Flow

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Issue in Brief:
The Environmental Risks of Biotech and Traditional Crops with Similar Traits Are the Same

The environmental risks of weediness and gene flow are no different for biotech crops than for similar conventional crops. As the genetic modifications to impart pest resistance and herbicide tolerance are being performed today on crop varieties already being grown commercially, there is a long historical baseline to assess potential risks.

The National Academies, Organization for Economic Cooperation and Development and others have determined that the environmental issues related to field testing and release of biotech crops for ecological effects are the same as for similar crops bred using conventional techniques. A 1987 report by the National Academies, for example, reached the following conclusion: "The risks associated with the introduction of r-DNA organisms are the same in kind as those associated with the introduction in the environment of unmodified organisms and organisms modified by other genetic techniques." Science-based practices in plant development, field testing and management developed over many years for traditional crops ensure the environmental safety of biotech crops.

Weediness
There has been no evidence that a domesticated crop plant can accidentally revert to a weedy condition because it has been modified using biotechnology. A 1987 report from the National Academies rated the chances of this happening as negligible.

Most cultivated crops do not possess the characteristics of a weed. Usually just the opposite is true. This is particularly so for crops that have undergone breeding over a long period of time, during which weedy traits-such as seed shattering, efficient seed-dispersal mechanisms, thorns and prolonged seed viability-are removed from the hybrid. Crop developers also add other traits to domesticated plants to enhance their productivity in a highly managed agricultural environment. These traits render them incapable of competing and surviving in the wild.

This was supported in a long-term study of the performance of biotech rapeseed, potato, corn and sugar beet in natural habitats. These crops were grown in 12 different habitats and monitored over 10 years. In no case were the genetically modified plants found to be more invasive or more persistent than their conventional counterparts.

For those crops that have weed-like characteristics, such as canola and sunflower, volunteerism may be an issue when uncollected seeds emerge the following year. Canola, for example, has been modified using both conventional techniques and biotechnology to tolerate herbicides. As volunteers of these plants have a selective advantage, weed control can become more difficult. In 1997, for example, a farmer in Alberta, Canada, planted three different herbicide-tolerant canolas in close proximity. Not surprisingly, the following year, resistant volunteers were discovered. Millions of acres of herbicide-tolerant canola are grown in Canada each year, and this is the only reported case of a problem developing. This is not an issue unique to biotech crops, and most growers avoid these problems by taking appropriate steps to manage gene flow.

Field tests of potentially weedy or invasive biotech crops are subject to more intensive scrutiny by the U.S. Department of Agriculture to avoid such problems. Where the potential for environmental damage is significant, USDA and the Environmental Protection Agency (for pest-protected plants) have the authority to discontinue field trials and suspend development of the plant.

For more on USDA and EPA regulations, click here.

Gene Flow
Gene movement is a natural exchange of genetic material; it plays a role in the ability of species to adapt and to evolve. It is a process that applies equally to biotech and traditional plants.

Gene flow in plants is pollen mediated; that is, it is the result of pollen moving from one plant to another where fertilization occurs and seeds are produced. It can occur only between individuals of the same or related species, and the resulting progeny contain half of the genes of each parent plant.

Concern has been expressed that gene flow could increase the weediness of wild relatives by imparting a trait that gives them a selective advantage. In the United States, most crop species originated elsewhere, so there is very little environmental risk from gene flow for commercial crops such as corn, wheat, soybean, alfalfa, cotton, barley, dry bean and tobacco.

But pollen-mediated gene flow can occur between different crop plants and wild relatives when they are grown close together. In such cases, however, a number of conditions have to be met: The plants must be in range for pollen exchange; they must flower at the same time; fertilization must occur and a stable seed produced; the seeds must survive and germinate; and its progeny must be fertile. Even when these conditions are met, absent strong selection pressures the trait is unlikely to be incorporated broadly into the wild population.

Nonetheless, regulators and plant developers carefully evaluate the likelihood of gene flow and its potential effects on the environment where it will be grown. The USDA is responsible for determining if a biotech plant has the potential to enhance the weediness of both the modified plant and any related, weedy species that may receive the gene. The USDA and EPA have determined that no biotech crops currently on the market pose an environmental threat.

For more on USDA and EPA regulations, click here.

A modest amount of gene flow may occur from field to field for some commodity products, but as all commercial biotech crops have full regulatory approval, this does not pose a safety issue. However, managing gene flow may be necessary to produce and deliver crops that meet specific quality standards. Identity-preserved or organic growers, for example, should adopt generally accepted practices to manage potential gene flow. Farmers growing biotech crops routinely discuss their planting intentions with neighbors to allow neighbors interested in meeting organic or other standards to make appropriate accommodations.

The impact of gene flow on genetic diversity, especially in centers of crop domestication, has also been cited as a concern with biotech crops. The potential gene flow of pest-protected corn to traditional landraces in Mexico, in particular, has been the topic of considerable interest.

Gene flow from plants designed to produce industrial enzymes and biopharmaceutical proteins is another potential concern but addressed through special growing systems dictated by regulatory agencies. For more information on plant made pharmaceuticals, click here.

Several technologies have been suggested to manage gene flow and to decrease the risk of herbicide-tolerant genes establishing themselves in wild populations. Sterile seed technology, dubbed "terminator" technology, has been developed, but public objections have kept it from being commercialized. Other approaches include chloroplast transformation and the use of tandem constructs that link the trait gene to another gene that codes for harmful traits in weeds, but not the crop. As these approaches become available, the potential risks associated with gene flow between crop and its wild relatives, already low, could be reduced even further.

Resources:
National Academies/National Research Council:

• Environmental Effects of Transgenic Plants: The Scope and Adequacy of Regulation (2002).
• Genetically Modified Pest-Protected Plants: Science and Regulation (2000).
• Field Testing of Genetically Modified Organisms: Framework for Decisions (1989).
• Introduction of Recombinant DNA-Engineered Organisms into the Environment (1987).

• Report of the Working Group on Harmonization of Regulatory Oversight in Biotechnology (June 9, 2000).
  Available in English and French.
• Safety Considerations of Biotechnology: Scale-Up of Crop Plants (1993).
• Traditional Crop Breeding Practices: An Historical Review to Serve as a Baseline for Assessing the Role of Modern Biotechnology (1993).

• Robert J. Cook, "Science-Based Risk Assessment for the Approval and Use of Plants in Agricultural and Other Environments," Agricultural Biotechnology and the Poor Report, Consultative Group on International Agricultural Research (2000).
• Council for Agricultural Science and Technology, Comparative Environmental Impacts of Biotechnology-derived and Traditional Soybean, Corn, and Cotton Crops (June 25, 2002).
  Executive summaries available in Chinese, English, French, Portuguese and Spanish.
• Crawley, M.J., et al. 2001. Biotechnology: Transgenic crops in natural habitats. Nature 409: 682-683.
• Ellstrand, N.C. 2001. When transgenes wander, should we worry? Plant Physiology 125: 1543-1545.
• Ellstrand, N.C., Prentice, H.C., and Hancock, J.F. 1999. Gene flow and introgression from domesticated plants into their wild relatives. Annu. Rev. Ecol. Syst. 30: 539-563.
  Read the abstract here (full article requires subscription).
• European Union, E.C.-Sponsored Research on the Safety of Genetically Modified Organisms: A Review of Results (2001).
• Food and Agricultural Organization, Gene Flow from GM to Non-GM Populations in the Crop, Forestry, Animal and Fishery Sectors, Electronic Forum on Biotechnology in Food and Agriculture: Conference 7 (2002).
• Friends of the Earth International, GMO Contamination Around the World (2001).
• Henry A. Wallace Center for Agricultural & Environmental Policy at Winrock International, Transgenic Crops: An Environmental Assessment (November 2000).
• Information Systems for Biotechnology, Workshop on Ecological Effects of Pest Resistant Genes in Managed Ecosystems, Bethesda, Maryland (January 31-February 3, 1999).
• 7th International Symposium on the Biosafety of Genetically Modified Organisms, Beijing, China (October 10-16, 2002).
• Jemison, J.M., and Vayda, M.E. 2001. Cross pollination from genetically engineered corn: Wind transport and seed source. AgBioForum 4(2): 87-92.
• Brian Johnson, "Genetically Modified Crops and Other Organisms: Implications for Agricultural Sustainability and Biodiversity," Agricultural Biotechnology and the Poor Report, Consultative Group on International Agricultural Research (2000).
• National Agricultural Biotechnology Council, Agricultural Biotechnology and Environmental Quality: Gene Escape and Pest Resistance, NABC Report 10 (1998).
• Ohio State University, Scientific Methods Workshop: Ecological and Agronomic Consequences of Gene Flow from Transgenic Crops to Wild Relatives, Columbus, Ohio (March 5-6, 2002).
• Riches, C.R., and Valverde, B.E. 2002. Agricultural and biological diversity in Latin America: implications for development, testing, and commercialization of herbicide-resistant crops. Weed Technol 16: 200-214.
• Tiedje, J.M., et al. 1989. The planned introduction of genetically engineered organisms: Ecological considerations and recommendations. Ecology 70: 298-314.

For more links, click here.