DD1996-10: Determination of Environmental Safety of 3751IR, an Imidazolinone-tolerant Corn (Zea mays L.) Hybrid developed by Pioneer Hi-Bred International Inc.
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This Decision Document has been prepared to explain the regulatory decision reached under the guidelines Dir94-08 Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits and its companion document Dir94-11 The Biology of Zea mays L. (Corn/Maize), and the guidelines Dir95-03 Guidelines for the Assessment of Livestock Feed from Plants with Novel Traits.
The Canadian Food Inspection Agency (CFIA), specifically the Plant Biosafety Office of the Plant Health and Production Division and the Feed Section of the Animal Health and Production Division, has evaluated information submitted by Pioneer Hi-Bred International Inc. regarding 3751IR corn. This plant was modified to express tolerance to imidazolinone herbicide. CFIA has determined that this plant with a novel trait (PNT) should pose no concerns with respect to environmental safety, the safety of livestock consuming feed derived from the PNT, and is considered substantially equivalent to corn products currently approved as livestock feed.
Unconfined release into the environment, including use as livestock feed of 3751IR corn and other Z. mays lines derived from it, without the introduction of any other novel traits, is therefore considered safe.
Table of Contents
- Brief Identification of the Plant with a Novel Trait (PNT)
- Background Information
- Description of the Novel Trait
- Assessment Criteria for Environmental Safety
- Nutritional Assessment Criteria for Use as Livestock Feed
- Regulatory Decision
I. Brief Identification of the Plant with a Novel Trait (PNT)
Designation(s) of the PNT: 3751IR
Applicant: Pioneer Hi-Bred International Inc.
Plant Species: Zea mays L. (corn/maize)
Novel Traits: Tolerance to imidazolinone herbicides
Trait Introduction Method: Selection of somaclonal variants from embryo cultures
Proposed Use of PNT's: For cultivation as hybrid grain corn in existing corn growing areas of Canada.
II. Background Information
Pioneer Hi-Bred International Inc. (Pioneer) has developed a corn hybrid, 3751IR, which is tolerant to an imidazolinone herbicide. This hybrid was derived from an inbred line, XA17, that was selected for tolerance to imidazolinone using plant tissue culture techniques.
Health Canada has determined that food derived from this corn is substantially equivalent to that derived from currently commercialized corn (June 27, 1995).
Pioneer has submitted data and information on the identity of 3751IR corn and characterization of the herbicide tolerance trait. Data from agronomic studies conducted in Canada and the United States, and data from proximate analyses were submitted. Pioneer has also submitted data from analyses of whole plant corn samples, taken from three sites in Canada, for levels of valine, leucine and isoleucine.
The Plant Biosafety Office of the Plant Health and Production Division, has reviewed the information submitted by Pioneer for the determination of environmental safety, in light of the assessment criteria described in the regulatory directive Dir94-08 Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits:
- potential of the PNT to become a weed of agriculture or 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 PNT to become a plant pest,
- potential impact of the PNT or its gene products on non-target species, including humans,
- potential impact on biodiversity.
The Feed Section of the Plant Health and Production Division, CFIA, has also reviewed the information submitted by Pioneer in light of the assessment criteria for determining safety and efficacy of livestock feed, as described in the regulatory directive Dir95-03 Guidelines for the Assessment of Livestock Feed from Plants with Novel Traits:
- potential impact on livestock, and
- potential impact on livestock nutrition.
III. Description of the Novel Trait
1. Imidazolinone Tolerance
- Imidazolinones comprise a class of herbicide which target and bind to the acetolactate synthase (ALS) enzyme thereby inhibiting the biosynthesis of branched chain amino acids, resulting in a decrease in protein synthesis and eventual death of the plant. ALS catalyses the first reaction in the biosynthesis of the essential branched chain amino acids valine, leucine and isoleucine and is active in the glycolytic pathway of plant metabolism.
- Imidazolinone tolerance in 3751IR corn results from a mutation in the ALS enzyme. The mutant form of ALS in 3751IR prevents the binding of imidazolinone herbicides to the enzyme. Imidazolinones applied at rates recommended for effective weed control are phytotoxic to currently cultivated corn varieties.
- The levels of valine, leucine and isoleucine are also regulated by feedback inhibition. Pioneer has provided literature references to show that the mutant ALS of the inbred line XA17, from which the hybrid 3751IR is derived, does not affect feedback inhibition and hence, the regulation of levels of these amino acids.
- The levels of valine, leucine and isoleucine in whole plant extracts of 3751IR and its counterpart 3751, were not statistically different, showing that the activity of the ALS enzyme in 3751IR has not been affected by the mutation.
2. Development Method
- Somatic embryos grown on imidazolinone enriched media were selected, and from these, the somaclonal variant cell line XA17 was isolated. This cell line was regenerated to a whole plant and crossed to the inbred line B73.
- The XA17/B73 line was backcrossed into each of two proprietary Pioneer inbreds which were then crossed to produce the hybrid 3751IR.
3. Stability of Trait
- The imidazolinone tolerance trait was shown to be stable and to display regular Mendelian segregation in progeny from XA17 crosses with several corn inbreds.
- 3751IR is homozygous for the imidazolinone tolerance trait. Homozygous progeny were found to be tolerant to imidazolinone at up to four times the recommended rate for soybeans. Heterozygous progeny, while expressing the herbicide tolerance trait, exhibited pronounced leaf chlorosis and stunted growth at these herbicide rates.
IV. Assessment Criteria for Environmental Safety
1. Potential of the PNT to Become a Weed of Agriculture or Become Invasive of Natural Habitats
The biology of corn (Zea mays), described in Dir94-11, shows that unmodified plants of this species are not invasive of unmanaged habitats in Canada. Corn does not possess the potential to become weedy due to traits such as lack of seed dormancy, the non-shattering aspect of corn cobs, and the poor competitive ability of seedlings. No competitive advantage was conferred to 3751IR corn, other than tolerance to imidazolinone. The mutation of the ALS in 3751IR has not significantly affected the physiology of the plant, as demonstrated by the normal levels of valine, leucine and isoleucine. It is therefore not expected that 3751IR would possess traits that would render it invasive of unmanaged habitats.
Corn is an open-pollinated species and 3751IR could cross-pollinate with other corn hybrids. The resulting progeny could acquire the herbicide tolerance gene. Progeny from self-pollination will also be imidazolinone tolerant. Heterozygous progeny express herbicide tolerance, although at a lower level than homozygotes. Imidazolinone tolerant corn volunteers will thus appear in subsequent crops.
Corn volunteers are commonly found in soybean fields when soybeans are cultivated in the year following corn. Pursuit® (imazethapyr) is currently registered for use in soybeans and will not be effective in controlling 3751IR corn volunteers. Corn volunteers are usually at an immature growth stage at soybean harvest time resulting in problems during harvest operations. While these volunteers could be managed by mechanical means and other available herbicides, the present use of imidazolinone herbicides in soybeans may be compromised. In general terms, growers must be made aware that imidazolinone tolerant corn volunteers will not be controlled in subsequent crops when imidazolinones are used as the sole weed control tool.
NOTE: A longer term concern, if there is general adoption of several different crop and specific herbicide weed management systems, is the development of crop volunteers with novel tolerances to specific herbicides. This could result in the loss of the use of these herbicides in some crop rotation cycles. Agricultural extension personnel, in both the private and public sectors, should therefore promote careful management practices for growers who use any of these herbicide tolerant crops.
The above considerations, together with the fact that the novel trait has no intended effects on weediness or invasiveness, led CFIA to conclude that 3751IR corn does not possess altered weed or invasiveness potential compared to currently commercialized corn.
2. Potential for Gene Flow to Wild Relatives Whose Hybrid Offspring May Become More Weedy or More Invasive
The biology of corn, as described in Dir94-11, indicates that there are no wild relatives in Canada that can freely hybridize with Zea mays. CFIA therefore concludes that gene flow from 3751IR corn to corn relatives is not possible in Canada.
3. Altered Plant Pest Potential
The novel trait in this plant does not inherently confer to 3751IR any potential to become a plant pest and Zea mays is not a plant pest in Canada (Dir94-11). Agronomic traits were shown to be within the range displayed by currently commercialized corn hybrids and the mutation of the ALS in 3751IR has not significantly affected the physiology of the plant, as demonstrated by the normal levels of valine, leucine and isoleucine. This led CFIA to conclude that 3751IR corn does not display any altered pest potential.
4. Potential Impact on Non-target Organisms
The mutant ALS in this hybrid has not significantly affected the biosynthesis of the branched-chain amino acids, valine, leucine and isoleucine indicating that the metabolism of the plant has not been unintentionally altered to produce any allergenic or toxic compounds. Based on the above, CFIA has determined that the unconfined release of 3751IR corn, when compared to currently commercialized corn, will not result in significantly altered impacts on interacting organisms, including humans.
5. Potential Impact on Biodiversity
3751IR corn does not possess novel phenotypic characteristics which would extend its use beyond the current geographic range of corn production in Canada. Since corn does not outcross to wild relatives in Canada, there will be no transfer of novel traits to unmanaged environments.
CFIA has therefore concluded that the potential impact of 3751IR corn on plant biodiversity is therefore equivalent to that of currently commercialized corn varieties.
V. Nutritional Assessment Criteria for Use as Livestock Feed
1. Nutritional Composition of PNT
No statistically significant differences in nutritional composition, i.e., crude protein, crude fat and crude fibre, were noted between the whole seed of 3751IR and those of current commercial corn cultivars. Valine, isoleucine and leucine contents in whole plants of 3751IR were compared to that of its closest counterpart 3751 to determine whether acetolactate synthase (ALS) activity of the PNT was affected by the mutation. No statistically significant differences in content of these amino acids were noted. These results collectively demonstrate that the mutation of the ALS enzyme in 3751IR, did not likely result in any secondary effects impacting on the composition or nutritional quality of the cultivar. Accordingly, 3751IR was judged to be substantially equivalent to traditional corn varieties in terms of nutritional composition.
2. Anti-Nutritional Factors
The parent plant Zea mays is not known for the production of anti-nutritional factors and the novel trait in 3751IR corn would not be expected to induce their synthesis.
VI. Regulatory Decision
Based on the review of data and information submitted by Pioneer Hi-Bred International Inc., and through comparisons of 3751IR with an unmodified Zea mays counterpart, the Plant Biosafety Office of the Plant Health and Production Division has concluded that the novel gene and its corresponding trait does not confer any intended or unintended ecological advantage to 3751IR following unconfined release.
Based on the review of submitted data and information, the Feed Section of the Plant Products Division has concluded that the novel trait does not in itself raise any concerns regarding the safety or nutritional composition of this line. Grain corn and several of its byproducts are currently listed in Schedule IV of the Feeds Regulations and are, therefore, approved for use in livestock feeds in Canada. As whole seeds and plants of 3751IR have been assessed and found to be substantially equivalent to traditional corn varieties, 3751IR and its byproducts are considered to meet the present definitions and are approved for use as livestock feed ingredients in Canada.
Unconfined release into the environment and use as livestock feed of 3751IR and other Z. mays lines derived from it, but not including those to which any other novel trait has been introduced, is therefore considered safe.
This bulletin is published by the Plant Health and Production Division. For further information, please contact the Plant Biosafety Office or the Feed Section at:
Plant Biosafety Office
Plant Health and Production Division
Plant Products Directorate
59 Camelot Drive, Nepean
Ontario, K1A 0Y9
Animal Health and Production Division
Animal Products Directorate
59 Camelot Drive, Nepean
Ontario, K1A 0Y9
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