DD1998-29: Determination of Environmental Safety of EXP1910IT, an Imazethapyr Tolerant Corn Hybrid developed by Zeneca Seeds

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Issued: 1996-04

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 Biotechnology Office (PBO) 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, CFIA, has evaluated information submitted by Zeneca regarding EXP1910IT corn. This plant was modified to express tolerance to imidazolinone (imazethapyr) herbicide. The CFIA has determined that this plant with novel traits (PNT) should pose no concerns with respect to environmental safety, the safety to 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 of the corn EXP1910IT is therefore authorized as of April 12, 1996. Also, any Z. mays line derived from EXP1910IT may be released provided that: no interspecific crosses are performed; the intended use of the plant is the same; and it is known following thorough characterization that these plants do not display any additional novel traits and are substantially equivalent to currently grown corn, in terms of their potential environmental impact and livestock feed safety.

Table of Contents

  1. Brief Identification of Plant with Novel Traits (PNT)
  2. Background Information
  3. Description of the Novel Traits
    1. Tolerance to imazethapyr
    2. Development Method and Stability of Trait
  4. Assessment Criteria for Environmental Safety
    1. Potential of the PNT to become a weed of agriculture or become invasive of natural habitats
    2. Potential for gene flow to wild relatives whose hybrid offspring may become more weedy or more invasive
    3. Altered Plant Pest Potential
    4. Potential Impact on Non-Target Organisms
    5. Potential Impact on Biodiversity
  5. Nutritional Assessment Criteria for Use as Livestock Feed
    1. Nutritional Composition of PNT
  6. Regulatory Decision

I. Brief Identification of the Plants with Novel Traits (PNT's)

Designation(s) of the PNT: MEXP1910IT

Applicant: Zeneca Seeds

Plant Species: Zea mays L. (corn/maize)

Novel Trait: Tolerance to imazethapyr

Trait Introduction Method: Mutation breeding

Proposed Use of PNT's: Cultivated as a hybrid grain corn for livestock feed and human consumption, not intended to be grown outside the usual production area for corn in Canada.

II. Background Information

Zeneca has developed a corn line which is tolerant to imazethapyr, an imidazolinone herbicide.

Health Canada has determined that food derived from this corn is substantially equivalent to that derived from currently commercialized corn.

Zeneca has submitted data and information on the identity of EXP1910IT corn and characterization of the herbicide tolerance trait. Data from agronomic studies conducted in Canada and data from enzyme activity experiments and proximate analyses were also reviewed.

The Plant Biotechnology Office of the Plant Health and Production Division, with input from the Plant Health Risk Assessment Unit, on behalf of the Science Division, CFIA, has reviewed the information submitted by Zeneca Seeds for the determination of environmental safety based on the following assessment criteria as 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 Animal Health and Production Division, CFIA, has also reviewed the information submitted by Zeneca Seeds based on the following 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
  • potential impact on livestock nutrition.

III. Description of the Novel Trait

1. Tolerance to imazethapyr

  • Imidazolinone herbicides, such as imazethapyr, target and bind 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.
  • Tolerance to imazethapyr in EXP1910IT results from a mutation in the ALS gene. The mutant form of ALS enzyme in EXP1910IT prevents the binding of imazethapyr to the enzyme. Imazethapyr applied at labelled rates is phytotoxic to currently cultivated corn varieties.
  • Zeneca Seeds has provided data to show that the activity of the mutant ALS enzyme is substantially equivalent to that of unmodified corn. These results demonstrate that the activity of the ALS enzyme in EXP1910IT has not been affected by the mutation in the ALS gene.
  • Zeneca Seeds has submitted data from field trials of EXP1910IT corn in southwestern Ontario which demonstrate that agronomic characteristics of EXP1910IT are substantially equivalent to those of it's non-mutated counterpart.

2. Development Method and Stability of Trait

  • Ethyl methanesulfonate (EMS) is a common and powerful chemical mutagen. In plants, EMS causes point mutations, but loss of a chromosome segment or deletion can also occur. As a result EMS has the potential to alter loci of particular interest without inducing a great number of closely linked mutations. In this instance, EMS generated a single base pair change in the amino acid sequence of ALS resulting in the modification to the allosteric binding site for the herbicide to the enzyme.
  • The trait is expressed as a single dominant gene, showing 1:1 segregation in backcross progenies. It has show stable inheritance over more than 8 generations since the original selections were made.

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 (Z. mays), described in Dir94-11, states 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 poor seed dormancy, the non-shattering aspect of corn cobs, and poor competitive ability of seedlings. The mutation of the ALS gene in EXP1910IT has not significantly affected the physiology of the plant. It is not expected that EXP1910IT would possess traits that would render it invasive of unmanaged habitats.

No competitive advantage was conferred to EXP1910IT corn other than tolerance to imazethapyr. Corn is an open-pollinated species and EXP1910IT could cross-pollinate with other corn hybrids. The resulting progeny could acquire the herbicide tolerance gene. Progeny from self-pollination will also be imazethapyr tolerant.

Corn volunteers are a common problem in soybean fields when soybeans are cultivated in the year following corn. The imazethapyr herbicide Pursuit® is not registered for the control of corn volunteers per se in soybeans, although phytotoxic effects have been observed when this herbicide is applied on corn. Phytotoxic effects would therefore not be observed in EXP1910IT corn volunteers in a subsequent soybean crop. Corn volunteers are usually at an immature growth stage at soybean harvest time which can cause problems during harvest operations. While this is considered a management problem, it merits consideration and has direct implications for growers.

NOTE: A longer term concern, if there is general adoption of herbicide tolerant crops, is the potential 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 to growers who use these herbicide tolerant crops.

The above considerations, together with the fact that the novel trait has no intended effects on weediness or invasiveness, lead the CFIA to conclude that EXP1910IT 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 Z. mays. The CFIA therefore concludes that gene flow from EXP1910IT 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 EXP1910IT any potential to become a plant pest and Z. mays is not a plant pest in Canada (Dir94-11). The agronomic characteristics of EXP1910IT were shown to be substantially equivalent to those of the non-mutated hybrid 3751, leading to the conclusion that plant pest potential was unlikely to have been altered.

4. Potential Impact on Non-Target Organisms

The mutant ALS gene in this hybrid has not significantly affected the activity of the ALS enzyme. The metabolism of the plant has thus not been altered to unintentionally produce any allergenic or toxic compounds. Based on the above, the CFIA has determined that the unconfined release of EXP1910IT corn, when compared to currently commercialized corn, will not result in significantly impact on interacting organisms, including humans.

5. Potential Impact on Biodiversity

EXP1910IT does not possess novel phenotypic characteristics which would extend their 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. The overall relative impact on plant biodiversity is neutral.

V. Nutritional Assessment Criteria for Use as Livestock Feed

1. Nutritional Composition of the PNT

No statistically significant differences in nutritional composition, i.e. crude protein, crude fat and crude fibre, were noted between the whole seed of EXP1910IT and those of current commercialized corn cultivars. Valine, isoleucine and leucine contents in whole plants of EXP1910IT were compared to that of its closest counterpart to determine whether the 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 gene in EXP1910IT did not result in any observable secondary effects on the composition or nutritional quality of the cultivar. Accordingly, EXP1910IT was judged to be substantially equivalent to traditional corn varieties in terms of nutritional composition.

VI. Regulatory Decision

Based on the review of data and information submitted by Zeneca Seeds, and through comparisons of EXP1910IT with unmodified Z. mays counterparts, the Plant Biotechnology Office of the Plant Health and Production Division, CFIA, has concluded that the novel gene and its corresponding trait do not confer any intended or unintended ecological advantage to EXP1910IT following unconfined release.

Based on the review of data and information submitted by Zeneca Seeds, the Feed Section of the Animal Health and Production Division, CFIA, has concluded that the novel trait does not in itself raise any concerns regarding the safety or nutritional composition of this line. Corn grain 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 EXP1910IT have been assessed and found to be substantially equivalent to traditional corn varieties, EXP1910IT and its byproducts are considered to meet the present ingredient definitions and are approved for use as livestock feed ingredients in Canada.

This bulletin is published by the Plant Health and Production Division, Canadian Food Inspection Agency. For further information, please contact the Plant Biosafety Office, Plant Health and Production Division or the Feed Section, Animal Health and Production Division at the following address:

Canadian Food Inspection Agency
59 Camelot Drive
Nepean, Ontario K1A 0Y9

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