Genetically Modified Pest-Protected Plants Science and Regulation (2000) / Chapter Skim
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1. Introduction and Background
1. Introduction and Background
Pages 19-39
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From page 19... ...
Pest control is a continuous process: as pest-protected plants are bred or new chemical pesticides are developed, pests evolve to overcome these control methods. Early methods to control pests include the use of sulfur fumigation in 1000 BC, ants for biocontrol in 324 BC, and crop rotation, controlled irrigation, and manure application during the Roman Empire.
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In the past, almost all commonly used plant breeding techniques began with artificial crosses, in which pollen from one plant is transferred to a reproductive organ of another, sexually compatible plant. Crossing allows for the combining of desirable traits, such as pest resistance and increased yield, from two or more plant cultivars.3 The objective is to combine these traits in a new cultivar that is superior to its parents.
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Sexual hybridization involves genes from sexually compatible species, which tend to be rather similar. Mutagenesis and the somaclonal variation process do not add genes, but rather modify existing genes.
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Foreign genes engineered into plants may or may not be homologous to genes already present in the plant or the food supply. 1.3 HISTORY AND IMPACT OF BREEDING METHODS Selection for desirable traits and hybridization has been used since the advent of human agriculture, but the logic underlying the inheritance of traits was not discovered until the middle 1800s.
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Since then, many plants have been bred to include desirable traits, such as pest resistance. Blight resistance traits from a Mexican potato species (Solanum demissum)
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After a trait is introduced by transgenic methods, the resulting plant can be sexually hybridized with useful varieties developed by conventional breeding. 1.4.1 Emergence of Recombinant DNA Methods Recombinant DNA methods emerged in the early 1970s after the discovery of restriction enzymes (Linn and Arber 1968; Meselson and Yuan 1968)
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1.4.2 Development of a Regulatory Framework for Transgenic Plants Concurrently with developments in the technical aspects of genetically engineering crops by using rDNA methods, regulatory concerns about the release of genetically engineered organisms into the environment emerged. The NIH guidelines in 1978 prohibited the environmental release of genetically engineered organisms unless exempted by the NIH director.
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Using the coordinated framework as a guide, USDA was the first agency to propose a regulation for the review of plants genetically modified with rDNA methods. On tune 16, 1987, a Federal Register notice established procedures for obtaining permits for releasing genetically engineered organisms into the environment in field trials (USDA 1987~.
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1986~; the gene confers resistance to TMV itself, and to viruses similar to TMV. A transgenic TMV-resistant tomato line developed by Monsanto was approved for field trials on March 23, 1988.
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Before transgenic crops were commercialized (from 1987 to 1994) , the USDA approved field trials of nine nematode-resistant transgenic pestprotected plant varieties, 45 fungus-resistant varieties, 17 bacteria-resistant varieties, 322 insect-resistant varieties, and 194 virus-resistant varieties.
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For a crop to achieve nonregulated status, "environmental assessment" and "determination of nonregulated status" documents are prepared by USDA; the documents address safety concerns under the FPPA such as impacts on agriculturally beneficial organisms, as well as addressing the agency's NEPA requirements (section 4.1.1~. 1.5.2 FDA Policy Also in 1992, FDA published a policy statement on its role under FFDCA for reviewing new plant varieties developed by all methods, whether transgenic or conventional (FDA 1992)
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EPA also proposed to exempt coat proteins of plant viruses and, as noted earlier, to exempt the genetic material that encodes pesticidal substances. In 1997, EPA published supplemental notices of proposed rulemaking for the FIFRA and FFDCA proposals published in 1994.
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EPA was not involved in reviewing the Flavr Savr tomato because the transgenic modification of the tomato did not involve a pesticidal trait. In December 1994, the first transgenic pest-protected plant achieved nonregulated status from USDA: a virus-resistant squash variety developed by Upjohn/Asgrow Seed Company that contained watermelon mosaic virus-2 coat protein and zucchini yellow mosaic virus coat protein.
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An exemption under FFDCA from the requirement of a tolerance for this Bt toxin and the genetic material necessary for its production eliminated the need to establish a maximal permissible level for residues of this Bt toxin in potatoes. For the exemption, EPA reviewed data on toxicity and allergenicity and convened a subpanel of the FIFRA Scientific Advisory Panel to discuss its review; the panel concluded that the Bt potato presented "little potential for human dietary toxicity." Table 1.3 lists the plant pesticides that have been reviewed by EPA.
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A total of 98 million acres were planted worldwide in 1999 (lames 1999~. Transgenic pest-protected crop varieties that contain Bt toxin transgenes make up a large percentage of the commercial transgenic crops.
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. In addition to the approved commercial transgenic crop varieties, thousands of transgenic varieties are undergoing field trials (USDA l999c)
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, and the EPA published findings of a specially convened scientific advisory panel on Bt resistance management (SAP 1998~. Under the registration process for plant pesticides, EPA requires a particular amount of non-Bt cotton or corn to be planted next to Bt cotton or corn to serve as a refuge for insects carrying Bt susceptible genes, and they also encourage the development of resistance management strategies for other transgenic Bt crops.
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The ability of transgenic plants to cross-pollinate with their wild relatives and form offspring with enhanced weediness has been investigated when herbicide-tolerant rapeseed plants were back-crossed with a wild relative. The hybrid progeny plants produced an equivalent amount of seed as the wild genotypes and were also herbicide-resistant (Snow et al.
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From page 37... ...
1.6.5 Regulatory Concerns The above concerns have led some to question the safety review that transgenic crops receive in the United States under the coordinated framework. Many believe that transgenic crops present substantial human health and ecological risks, and that these are not properly assessed by the regulatory framework.
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, which proposed guiding principles that helped shape national policy for the review of genetically engineered organisms. In 1989, the NRC convened a committee to establish a framework for decisions regarding the field testing of genetically engineered organisms (NRC 1989~; the criteria and methods for evaluation suggested by that committee have been guiding USDA oversight of field trials for transgenic crops in the last 10 years.
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Conventional pest-protected plants are discussed for scientific comparisons. Given impending decisions with respect to the EPA plant-pesticide rule, the committee focused on the EPA's proposed rule, but also addressed the roles of the EPA, USDA, and FDA under the coordinated framework.
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