DD1999-31: Determination of the Safety of Cyanamid Crop Protection's Imidazolinone-Tolerant Spring Wheat
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This Decision Document has been prepared to explain the regulatory decision reached under the guideline Dir94-08 Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits and the companion document Dir1999-01 The Biology of Triticum aestivum (Wheat) and the guidelines Dir95-03 Guidelines for the Assessment of Plants with Novel Traits as Livestock Feed.
The Canadian Food Inspection Agency (CFIA), specifically the Plant Biotechnology Office of the Plant Health and Production Division and the Feed Section of the Animal Health and Production Division, with input from the Plant Health Risk Assessment Unit of the Science Division, has evaluated information submitted by Cyanamid Crop Protection regarding the imidazolinone tolerant spring wheat line SWP965001. It has been determined that this plant with a novel trait does not present altered environmental interactions, is substantially equivalent to wheat approved as livestock feed and does not pose any additional plant pest risk when compared to currently commercialized wheat varieties in Canada.
Unconfined release of SWP965001 into the environment, including feed use, is therefore authorized as of March 3, 1998. Any other T. aestivum lines resulting from the same mutation event and all their descendants may be imported and/or released provided no inter-specific crosses are performed, provided the intended use is similar, provided it is known following thorough characterization that these plants do not display any additional novel traits, and provided that the resulting lines are substantially equivalent to currently grown T. aestivum in terms of their potential environmental and plant health impacts.
SWP965001 is now subject to the same phytosanitary import requirements as its unmodified counterparts.
Please note that, while determining the environmental and livestock feed safety of plants with novel traits is a critical step in the commercialization of these plant types, other requirements still need to be addressed, such as Food Assessments (Health Canada) and Variety Registration (CFIA).
Table of Contents
- Brief Identification of the Plant with a Novel Trait (PNT)
- Background Information
- Description of the Novel Traits
- Imidazolinone Tolerance
- Development Method
- Stable Expression
- Assessment Criteria for Environmental Safety
- Potential of the PNT to become a Weed of Agriculture or to be Invasive of Natural Habitats
- Potential for Gene Flow to Relatives Whose Hybrid Offspring May Become More Weedy or More Invasive
- Altered Plant Pest Potential
- Potential Impact on Non-Target Organisms
- Potential Impact on Biodiversity
- Nutritional Assessment Criteria for Use as Livestock Feed
- Antinutritional Factors
- Nutritional Composition of the PNT
- Regulatory Decision
I. Brief Identification of the Plant with a Novel Trait (PNT)
Designation(s) of the PNT: SWP965001
Applicant: Cyanamid Crop Protection
Plant Species: Wheat (Triticum aestivum)
Novel Traits: Imidazolinone tolerance, specifically tolerance to Cyanamid's AC299 263 herbicide (imazamox, active ingredient)
Trait Introduction Method: Chemically induced seed mutagenesis
Proposed Use of PNT's: Production of T. aestivum for human food and livestock feed. This material will not be grown outside the normal production area for wheat.
II. Background Information
Cyanamid Crop Protection has developed a spring wheat line tolerant to imidazolinone herbicides, specifically to Cyanamid's AC 299 263 herbicide, currently registered in Canada as a post-emergence herbicide for the control of various broadleaf and grass weeds. This T. aestivum line, referred to as SWP965001 in the present document, exhibited no significant injury when treated with AC 299 263 at normal field application rates. This will allow the use of imidazolinone as a post-emergent herbicide on wheat crops, thus providing an alternative means of weed control in wheat production. Some canola and corn lines tolerant to imidazolinones have been approved for unconfined environmental release in Canada (see decision documents DD95-03 and DD96-10).
SWP965001 was developed using chemical mutagenesis. The herbicide tolerant phenotype results from the modification of a gene belonging to the acetohydroxyacid synthase (AHAS) multigene family, such that this enzyme, the target of imidazolinone herbicides, is no longer affected by imidazolinones.
SWP965001 has been field tested in Canada in 1997 under confined conditions in the provinces of Alberta, Manitoba, and Saskatchewan.
Cyanamid Crop Protection has provided data on the identity of SWP965001, a detailed description of the modification method and breeding history, information on the modified gene, the resulting protein and its mode of action and the stability of trait expression. References to scientific publications were also included.
Agronomic characteristics such as grain yield, days to heading, days to maturity, plant height, production of oil and protein, and disease susceptibilities were compared with those of unmodified T. aestivum counterparts.
The Canadian Food Inspection Agency (CFIA) reviewed the above information, in accordance with the following assessment criteria for determining environmental safety of plants with novel traits, as described in regulatory directive Dir94-08:
- potential of the PNTs to become weeds of agriculture or to be invasive of natural habitats,
- potential for gene-flow to wild relatives whose hybrid offspring may become more weedy or more invasive,
- potential for the PNTs to become plant pests,
- potential impact of the PNTs or their gene products on non-target species, including humans,
- potential impact on biodiversity
The Feed section of the Animal Health and production Division has also reviewed the above information in light of the assessment criteria for determining safety and efficacy of livestock feed as described in DIR95-03. We have considered:
- Potential impact to livestock
- Potential impact to livestock nutrition
III. Description of the Novel Trait
1. Imidazolinone Tolerance
- Imidazolinone herbicides are active against the enzyme acetohydroxyacid synthase (AHAS), also known as acetolactate synthase (ALS) or acetolactate pyruvate-lyase.
- This enzyme catalyzes the first step in the biosynthesis of the essential branched chain amino acids isoleucine, leucine and valine. Herbicide induced AHAS inhibition results in a lethal decrease in protein synthesis. Unmodified wheat is not tolerant to imidazolinones, while soybeans, peas, white beans and kidney beans are naturally tolerant to them.
- Depending on the species, plants contain single or multiple copies of the AHAS genes. The genome of T. aestivum is believed to contain an AHAS multigene family.
- Modifications of AHAS genes in various plant species can result in herbicide tolerant phenotypes and typically consist of one amino acid substitution, sufficient to alter the binding site for imidazolinones such that the herbicide no longer inhibits the AHAS enzyme. Several modified AHAS plants have been isolated. References to relevant scientific publications were provided by the proponent.
- Cyanamid Crop Protection selected four T. aestivum lines FS1, FS2, FS3 and FS4, with altered AHAS enzymes not inhibited by the herbicide. SWP965001 is derived from FS2.
- The novel imidazolinone tolerance is under the control of the native AHAS promoter and is believed to be constitutively expressed. The sequence of the modified AHAS gene was submitted for both the FS2 and FS4 lines.
- The levels of valine, leucine and isoleucine produced in T. aestivum are regulated by feedback inhibition. Cyanamid Crop Protection has provided literature references and data to support the claim that modified AHAS does not affect feedback inhibition and hence, the regulation and the levels of theses amino acids.
2. Development Method
- The original mutant line was isolated from a population derived by chemical-induced mutagenesis of seed of the winter wheat cultivar Fidel with sodium azide. Four imidazolinone-tolerant seedlings, FSI, FS2, FS3 and FS4, were selected in the presence of herbicide. SWP965001 is derived from the selection line FS2.
- SWP965001 was derived from an initial cross of FS2 to the spring wheat cultivar Grandin, followed by two backcrosses to Grandin. As a result, 87.5% of the genetic information is from the Grandin parent and the remaining 12.5% is from Fidel.
3. Stable Expression
- The imidazolinone tolerance trait from FS2 was shown to segregate according to that expected for a single semidominant allele. SWP965001, which is several generations removed from the original mutation event, still consistently shows imidazolinone tolerance.
IV. Assessment Criteria for Environmental Safety
The CFIA has evaluated data submitted by Cyanamid Crop Protection for agronomic performance of SWP965001 and some sister lines as well as Grandin, the recurrent parent and major genetic contributor to these imidazolinone tolerant lines. Data were submitted for seed production, seed germination, days to heading, days to maturity, and plant height. A statistically significant difference in height was observed for SWP965001 and Grandin; the mutant line was significantly taller than the parent line. This difference was attributed to segregation of a dwarfing gene as supported by the segregation of sister lines containing the same modified AHAS genes into two height groups. A statistical difference in days to maturity was also observed but the variation was found to be within the normal range for this trait in unmodified wheat. No significant difference in the yield, seed germination, or days to head was noted. Data were also submitted to support the absence of effect of the AHAS mutation on the interspecific hybridization potential.
Valine, isoleucine and leucine contents of SWP965001 were comparable to those of the commercial cultivars assayed demonstrating that AHAS activity of the PNT was not affected by the mutation. SWP965001 has no additional novel traits that could confer any ecological advantage over unmodified wheat.
These results collectively demonstrate that the mutation of the AHAS gene in SWP965001 did not result in any apparent secondary effects which could impact on the environmental safety of this line.
1. Potential of the PNT to become a Weed of Agriculture or be Invasive of Natural Habitats
The biology of T. aestivum, described in Dir1999-01, shows that unmodified plants of this species are not invasive of unmanaged habitats in Canada. According to the information provided by Cyanamid Crop Protection, SWP965001 was determined not to be different from its counterparts in this respect. The mutation of the AHAS gene in SWP965001 has not significantly affected the physiology of the plant, as supported by agronomic and compositional data. It is therefore not expected that SWP965001 would possess traits that would render it invasive of unmanaged habitats. No competitive advantage was conferred to SWP965001, other than tolerance to imidazolinone.
Imidazolinone tolerance will not cause SWP965001 to become more weedy or invasive in managed habitats than non-transformed T. aestivum. Imidazolinone-tolerant wheat volunteers will not be controlled in subsequent crops if imidazolinone is used as the sole weed control tool. However, control of imidazolinone tolerant weeds, or imidazolinone tolerant wheat as a volunteer weed in other crops or in fallow ground, can readily be achieved by the use of classes of herbicides other than imidazolinones, or by mechanical means.
The above considerations have led the CFIA to conclude that SWP965001 has no altered weed or invasiveness potential when compared with currently commercialized wheat varieties.
NOTE: A longer term concern, should there be general adoption of several different crop/specific herbicide weed management systems, is the potential development of crop volunteers with a combination of novel resistances to different herbicides. This could result in the loss of the use of these herbicides and any of their potential benefits. Therefore, agricultural extension personnel, in both the private and public sectors, should promote careful management practices for growers who use these herbicide tolerant crops, to minimize the development of multiple resistance.
2. Potential for Gene Flow to Relatives Whose Hybrid Offspring May Become More Weedy or More Invasive
The biology of wheat, as described in Dir1999-01, indicates that it is primarily a self- pollinated crop and that there are no wild or weedy relatives in Canada that can freely hybridize with T. aestivum.
Other than T. aestivum, the only other Triticum species commonly found in North America is the cultivated T. turgidum commonly referred to as durum wheat. T. aestivum does not easily form interspecific or intergeneric hybrids (Kimber and Sears, 1987).
The CFIA therefore concludes that gene flow from SWP965001 to wild or weedy relatives is unlikely to occur in Canada.
3. Altered Plant Pest Potential
The intended effect of the novel trait is unrelated to plant pest potential, and T. aestivum is not a plant pest in Canada. In addition, agronomic characteristics of SWP965001 were shown to be within the range of values displayed by currently commercialized T. aestivum varieties, leading to the conclusion that plant pest potential has not been inadvertently altered.
The CFIA has therefore determined that SWP965001 is unlikely to display any altered pest potential.
4. Potential Impact on Non-Target Organisms
Single amino acid modifications of the AHAS enzyme, which alters the herbicide binding site on the enzyme, is the molecular basis for imidazolinone tolerance in several plants. Cyanamid has submitted data and information indicating that the modified AHAS is substantially equivalent to its unmodified counterparts. The mutant AHAS in SWP965001 has not significantly affected the biosynthesis of the branched- chain amino acids, valine, leucine and isoleucine. Because of the specificity of the modification, unintentional alteration of the plant's metabolism is unlikely. Production of new allergenic or toxic compounds is also unlikely.
The CFIA has therefore determined that the unconfined release of SWP965001 will not result in altered impacts on interacting organisms, including humans, compared with currently commercialized counterparts.
5. Potential Impact on Biodiversity
SWP965001 has no novel phenotypic characteristics which would extend its use beyond the current geographic range of spring wheat production in Canada. Since wheat does not outcross under natural conditions to wild or cultivated/naturalized relatives in Canada, the transfer of novel traits to other plant species in unmanaged environments is highly unlikely. The CFIA has therefore concluded that the potential impact on biodiversity of SWP965001 is equivalent to that of currently commercialized wheat lines.
V. Nutritional Assessment Criteria as Livestock Feed
1. Antinutritional Factors
Wheat is not known for the production of antinutritional factors and the imidazolinone tolerance trait is not expected to induce their synthesis.
2. Nutritional Composition
Comparisons of branched chain amino acids, fat , fibre and ash from the PNT line and its parent line were made using samples from two sister lines and seven control lines. The fat in the PNT line was slightly, but significantly lower than the control lines. Protein, branched chain amino acids, fibre and ash were not significantly different when the PNT and the control lines were compared.
Protein, fat and fibre concentrations were within the published range for wheat. The observed variations in nutritional composition were judged to arise from normal variability rather than as a result of the novel trait. The CFIA has determined that line SWP965001 is substantially equivalent to traditional wheat varieties.
VI. Regulatory Decisions
Based on the review of data and information submitted by Cyanamid Crop Protection, including comparisons of SWP965001 with unmodified T. aestivum counterparts, the Plant Health and Production Division has concluded that the modified gene product and its corresponding novel trait will not confer any intended or unintended ecological advantage to SWP965001 following unconfined release. SWP965001 was also determined not to pose any additional plant pest risk compared to its unmodified counterparts.
If at any time, Cyanamid Crop Protection becomes aware of any information regarding risk to the environment, or risk to animal or human health, that could result from release of these materials in Canada, or elsewhere, Cyanamid Crop Protection must immediately provide such information to the CFIA. On the basis of such new information, the CFIA may re-evaluate the potential impact of the release and re-evaluate its decision.
Unconfined release of SWP965001 into the environment, including feed use, is therefore authorized. Any other T. aestivum lines derived from SWP965001 and descendants of other lines with the same modification are also approved provided no inter-specific crosses are performed, provided the intended use is similar, provided it is known following thorough characterization that these plants do not display any additional novel traits and that the resulting lines are substantially equivalent to currently grown T. aestivum in terms of their potential environmental and plant health impacts.
SWP965001 is now subject to the same phytosanitary import requirements as its unmodified counterparts.
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