Genetically Modified Pest-Protected Plants Science and Regulation (2000) / Chapter Skim
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3. Crossroads of Science and Oversight
3. Crossroads of Science and Oversight
Pages 104-143
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From page 104... ...
and durum wheat (T. durum Desk.: stem rust (or black rust)
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From page 105... ...
For example, stem rust tends to require higher temperatures than leaf rust, which requires higher temperatures than stripe rust; hence, stem rust is usually more damaging in the northern Great Plains, leaf rust in the southern Great Plains and the East, and stripe rust in the West. Of the three diseases, stem rust can cause the more devastating epidemics; for example, in 1916, a stem rust epidemic was estimated to have reduced total US wheat production by 38% (Loegering 1967~.
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From page 106... ...
has defined durable resistance as the "resistance that remains effective during prolonged and widespread use in an environment favorable to the disease." Considering the definition, genes for durable resistance are identified only after they have been deployed in widely grown cultivars. New genes for pest-protection are constantly being searched for in wheat and its wild relatives, and plant breeders try to create new combi
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From page 107... ...
In the United States, epidemics are localized, but the yield losses due to plant susceptibility to stem rust were as high as 56.5% in North Dakota and 51.6% in Minnesota in 1935 (Roelfs 1979~. For leaf rust, the yield losses due to susceptibility were estimated at 50% in Georgia in 1972.
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From page 108... ...
1987~. Stem rust tends to reduce the flow of photosynthate and nitrogen to the grain; but because nitrogen is mobilized early in grain development, the overall result of stem rust is generally an increase in protein content in the grain, possibly including shriveled kernels.
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From page 109... ...
However, low rates of adoption of Bt potato may ultimately be due to the need for potato growers to use chemicals to control insect pests other than the Colorado potato beetle. In those cases, protection from the Colorado potato beetle may not offset the cost of the chemicals and the transgenic seed (Gianessi and Carpenter 1999~.
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From page 110... ...
For example, tests for nontarget effects on honeybee larvae used a bioassay in which 5 uL of a Bt-toxin solution was pipetted into the bottom of larval cells and observations for potential mortality were made (Maggi 1993b) ; this approach would be better for a contact toxin than for toxins such as Bt toxin, which must be ingested.
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From page 111... ...
, but potato beetles do not typically feed on the tubers. Corn Unlike the Colorado potato beetle, which can devastate potato production in some areas when not controlled with insecticides, the European corn borer, which is the major target of transgenic Bt field corn, has not commonly been controlled with insecticides.
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From page 112... ...
For example, the southwestern corn borer, a major corn pest in some areas of the Midwest, can be controlled by Bt corn; and the corn earworm, a minor pest of field corn but a major pest of sweet corn, is also a potential target. A recent USDA study (1999d)
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From page 113... ...
Likewise, the committee recommends that EPA should provide guidelines for determining the most ecologically relevant test organisms and test procedures for assessing nontarget effects in specific cropping systems. Peer-reviewed studies (for example, MacIntosh et al.
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From page 114... ...
Corn earworm is also subject to selection pressure from Bt toxins in Bt cotton, since this pest feeds on a number of crops, including cotton, where it is known as the cotton bollworm (EPA and USDA 1999~. All the commercial cultivars provide substantial protection against the European corn borer (Ostlie et al.
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From page 115... ...
In the corn study, the half-life of CrylAb Bt toxin from pulverized corn placed in vials of soil was 1.5 days, and 90% of the activity was lost in 15 days. In the similar study of cotton plant material that produced CrylAc toxin, the half-life was 41 days, and 90% of the activity was expected to be lost in 136 days (on the basis of extrapolation)
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From page 116... ...
To slow the evolution of adaptation to Bt toxins by corn earworms, very large refuges of non-Bt cotton are needed (Gould and Tabashnik 1998~. The toxin titer in Bt cotton appears to be at least close to a high dose for the pink bollworm in early-season Bt cotton, but it is unlikely to achieve a high dose late in the season.
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From page 117... ...
· Assessment of sequence similarity of about 10-15 amino terminal amino acids and up to three short internal protein sequences. · Determination of similar toxicities of the proteins to one or two .
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From page 118... ...
Because the proteins reach the gastric fluids first, the lack of degradation by intestinal fluids would be unimportant unless an individual lacked active gastric digestion. Acute Toxicity to Mice Mice were given oral doses of the microbially-produced Bt toxins about 100-1000 times the acute dose that they would encounter in consuming one-tenth of their body weight in plant material.
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From page 119... ...
Although the sequence of the cloned gene is usually known and will largely remain intact during plant expression, modifications such as amino acid substitutions, proteolytic processing, and glycosylation are all possible. Therefore, it would be helpful to use plant-produced defensive substances in as many tests as is feasible.
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From page 120... ...
Virus-protected potato has also been approved for marketing, and more than 20 other domesticated species have been field-tested to evaluate transgenic protection against viruses (chapter 1, tables 1.4 and 1.5~. Squash Varieties of domesticated Cucurbita pepo commonly known as zucchini, yellow crookneck squash (summer squash)
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From page 121... ...
, and Upjohn/Asgrow used viral coat protein genes to achieve similar objectives in transgenic yellow crookneck squash. Upjohn/Asgrow's first commercial transgenic product was Freedom II, which was protected from WMV2 and ZYMV and was deregulated in 1994; it exhibits strong protection from the targeted viruses (Fuchs and Gonsalves 1995; Tricoli et al.
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From page 122... ...
1999~. The major environmental risks that have been discussed in connection with virus-protected crops pertain to effects of viral coat protein genes on the pathogenicity of other viruses (Falk and Bruening 1994)
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From page 123... ...
1978~. To check for viral infections in FLCP populations, Asgrow conducted a survey in 1993.
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From page 124... ...
Surveys of natural FLCP populations for the incidence and severity of ZYMV and WMV2 infections suggest that resistance to these viruses will confer little, if any, selective advantage, because disease caused by these viruses is apparently not among the factors important to the survival or reproductive success of FLCP. The issue merits further empirical study, especially because selectively neutral crop genes are often maintained in the gene pools of wild and weedy plants (for example, Whitton et al.
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From page 125... ...
In cases like this, the committee recommends that USDA should require original data to support agency decision-making concerning transgenic crops when published data are insufficient. In cases when crucial scientific data are lacking about the potential impacts of gene flow on wild or weedy relatives, the committee recommends delaying approval of deregulation pending sufficient data (for example, surveys from several years over several regions)
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From page 126... ...
As with Asgrow's squash, the papaya's viral coat protein is not expected to jeopardize human health, because consumers already ingest this compound in nontransgenic food. Gene flow to feral or wild relatives was not an issue because no wild relatives occur in Hawaii, Puerto Rico, or Florida, and the crop itself is not weedy.
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From page 127... ...
. EPA proposed to regulate "a pesticidal substance that is produced in a living plant and the genetic material necessary for the production of the substance, where the substance is intended for use in the living plant." That definition excludes pesticidal substances such as pyrethrum and neem, that are produced by plants but are then extracted from the plants before being used although substances used in this way are subject to EPA regulation as conventional pesticides.
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From page 128... ...
As long as the genetic material comes from a sexually compatible plant, the plant-pesticide is exempt, regardless of whether the method of transferring genetic material uses sexual crosses or transgenic technology. The committee recognizes the realistic limitations of overseeing the pesticidal substances in conventional pest-protected plants and, given their history of safe use, recognizes that there are practical reasons for exempting those substances.
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From page 129... ...
Major portions of the 1994 and 1997 documents explain the scientific rationale for the categorical exemption. The 1994 document states that "since traits can be passed through a plant population by sexual recombination, it is reasonable to predict that, in a sexually compatible population, new exposures of organisms that associate with plants in the population to the pesticidal substance are unlikely." It might be appropriate to exempt those plant protestants, but the rationale in the above statement and in other statements in the 1994 document disregards the following: · Even for sexually compatible populations that are theoretically capable of natural cross-fertilization in the wild, there is no substantial passing of traits between populations unless the populations are in close proximity.
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From page 130... ...
EPA has determined that changes in the levels of these pesticidal substances present a reasonable certainty of causing no harm because the highest levels likely to be attained in plants are not likely to result in overall significantly different dietary exposure. The exemption includes all genes derived from sexually compatible plants and promoter sequences from any origin.
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From page 131... ...
. EPA does not believe that levels of pesticidal substances that are the subject of the proposed exemption (59 Fed.
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From page 132... ...
Although the same scientific arguments can be made for the risks posed by conventional pest-protected plants, which are not subject to regulation under the coordinated framework, lack of experience with transgenic pest-protected products and public concern with these products constitute practical reasons for not granting a categorical exemption to transgenic pest-protectants derived from sexually compatible species. In summary, the committee recommends that Given that transfer and manipulation of genes between sexually compatible plants could potentially result in adverse effects in some cases (for example, modulation of a pathway that increases the concentration
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From page 133... ...
However, the committee questions the categorical exemption of all viral coat proteins under FIFRA due to concerns about outcrossing with weedy relatives. Although ecological concerns are discussed and a more restrictive exemption that considers outcrossing is presented, the proposed rule favors complete exemption of VCPs.
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From page 134... ...
there is a need to consider separately the impact of such substances on nontarget species and the potential for the genes that code for these substances to move to feral populations or weedy relatives of the crop, where they could increase recipient plants' fitness. Categorical exemption under FIFRA might not be scientifically justifiable.
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From page 135... ...
Because the Coordinated Framework for the Regulation of Biotechnology was designed for transgenic products (see chapter 1) and the agencies do not actively assess conventional pest-protected plant products, the following questions focus on transgenic pest-protected plant products.
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From page 136... ...
136 GENETICALLY MODIFIED PEST-PROTECTED PUS: SCIENCE ED ~GU~TION ing concerns are not dependent on the method used to produce the plant (section 2.2.1~. 3.3.1 Health Concerns: Guiding Principles The principles in the following questions could be used to determine when a detailed analysis of health risks is warranted for transgenic pestprotected plants.
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From page 137... ...
Given that transfer and manipulation of genes between sexually compatible plants could potentially result in adverse effects (for example, modulation of a pathway increases the concentration of a toxicant) , the categorical exemption of pest Protestants solely on the basis of derivation from sexually compatible plants could be scientifically unsound in some cases.
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From page 138... ...
EPA's categorical exemptions of transgenic plants that have sexually compatible, nontoxic, and viral coat proteins are not in agreement with these principles in some cases. USDA analyzes these concerns according to risks posed to agriculture, so weedy relatives with agricultural effects are of concern; its methods are similar to the following questions, although original data are not always used.
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From page 139... ...
In addition to the recommendations in section 3.1.4, the committee recommends that USDA should research, publicize, and periodically revise lists of plant species with feral populations or wild relatives in the United States in order to evaluate the impacts of outcrossing. 3.4 RESEARCH NEEDS The committee realizes that there remain some uncertainties regarding the use of pest-protected plants, including transgenic pest-protected plants.
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From page 140... ...
Research is needed to determine the baseline concentrations of secondary compounds in plant species of potential dietary or other toxicological concern and to determine how these compounds may vary depending on the genetic background and environmental conditions (see section 2.5.2 and recommendations in section 3.2.4~. For longterm toxicity testing, research should be conducted to examine whether longterm feeding of transgenic pest-protected plants to animals whose natural diets consist of large quantities and the type of plant material being tested (for example, grain or forage crops fed to livestock)
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From page 141... ...
Research to assess gene flow and its potential consequences should be conducted (section 2.7~. A list of plants with wild or weedy relatives in the United States should be established in an accessible public database (see section 3.3~.
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From page 142... ...
· USDA should research, publicize, and periodically revise lists of plant species with feral populations or wild relatives in the United States in order to evaluate the impacts of outcrossing.
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From page 143... ...
, and given public controversy regarding transgenic products, EPA should reconsider its categorical exemption of transgenic pest-protectants derived from sexually compatible plants. · EPA should not categorically exempt viral coat proteins from regulation under FIFRA.
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