DD2008-69: Determination of the Safety of Pioneer Hi-Bred Production Ltd.'s Sulfonylurea - Tolerant ExpressSun™ Sunflower (Helianthus annuus) L. SU7

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Issued: 2008-02

This Decision Document has been prepared to explain the regulatory decision reached under Dir94-08 Assessment Criteria for Determining Environmental Safety of Plants with Novel Traits and its companion document BIO2005-01 The Biology of Helianthus annuus L. (Sunflower) and Dir95-03 Guidelines for the Assessment of Novel Feeds: Plant Sources.

The Canadian Food Inspection Agency (CFIA), specifically the Plant Biosafety Office of the Plant Health and Biosecurity Directorate, the Biotechnology Environmental Release Assessment Unit of the Science Strategies Directorate and the Animal Feed Division of the Animal Health Directorate, has evaluated information submitted by Pioneer Hi-Bred Production Ltd. regarding the ExpressSun™ sunflower SU7, which is tolerant to the sulfonylurea herbicide Express®. The CFIA has determined that this plant with a novel trait does not present a greater risk to the environment, nor as a novel feed, does it present livestock feed safety concerns when compared to currently commercialized sunflower varieties in Canada.

Taking into account these evaluations, unconfined release into the environment and livestock feed use of ExpressSun™ sunflower SU7 are therefore authorized by the Plant Biosafety Office of the Plant Health and Biosecurity Directorate and the Animal Feed Division of the Animal Health Directorate as of January 2, 2008. Any sunflower lines derived from ExpressSun™ sunflower SU7 may also be released into the environment or used as livestock feed, provided (i) no inter-specific crosses are performed, (ii) the intended uses are similar, and (iii) it is known based on characterization that these plants do not display any additional novel traits and are substantially equivalent to currently grown sunflower in Canada, in terms of their potential environmental impact and livestock feed safety.

ExpressSun™ sunflower SU7 is subject to the same phytosanitary import requirements as its unmodified counterparts.

Please note that the assessment of livestock feed safety and environmental safety are critical steps in the potential commercialization of these plant types. Other requirements, such as the evaluation of food safety by Health Canada, have been addressed separately from this review.

Table of Contents

I. Brief Identification of the Modified Plant

II. Background Information

III. Description of the Novel Trait

  1. Development Method
  2. Sulfonylurea Tolerance
  3. Stable Expression

IV. Assessment Criteria for Environmental Safety

  1. Potential of ExpressSun™ Sunflower SU7 to become a Weed of Agriculture or to be Invasive of Natural Habitats
  2. Potential for Gene Flow from ExpressSun™ Sunflower SU7 to Relatives Whose Hybrid Offspring May Become More Weedy or More Invasive
  3. Altered Plant Pest Potential of ExpressSun™ Sunflower SU7
  4. Potential Impact of ExpressSun™ Sunflower SU7 on Non-Target Organisms
  5. Potential Impact of ExpressSun™ Sunflower SU7 on Biodiversity

V. Criteria for the Livestock Feed Assessment

  1. Potential Impact of ExpressSun™ Sunflower SU7 on Livestock Nutrition
  2. Potential Impact of ExpressSun™ Sunflower SU7 on Livestock and Workers/By-standers

VI. New Information Requirements

VII. Regulatory Decision

Appendix 1: ExpressSun™ Sunflower SU7 Herbicide Tolerance Stewardship Plan

I. Brief Identification of the Modified Plant

Designation of the Modified Plant: ExpressSun™ sunflower SU7

Applicant: Pioneer Hi-Bred Production Ltd.

Plant Species: Sunflower (Helianthus annuus L.)

Novel Traits: Tolerance to sulfonylurea herbicides

Trait Introduction Method: Chemically induced seed mutagenesis

Proposed Use of the Modified Plant: Production of H. annuus for human food and livestock feed. This material will not be grown outside the normal production area for sunflower.

II. Background Information

Pioneer Hi-Bred Production Ltd. has developed a sunflower tolerant to sulfonylurea herbicides. This sunflower, designated ExpressSun™ sunflower SU7, was developed to allow in-crop applications of sulfonylurea herbicides at normal field application rates. This will allow post-emergent use of sulfonylurea in sunflower crops, thus providing an alternative means of weed control in sunflower production.

The sulfonylurea tolerance trait was introduced into sunflower by chemical mutagenesis. The herbicide tolerance trait is conferred by a single point mutation in the acetohydroxyacid synthase (AHAS) gene such that this enzyme, the target of sulfonylurea herbicides, is no longer affected by sulfonylurea herbicides.

ExpressSun™ sunflower SU7 was field tested in the US in 2003, in regions representative of Canadian sunflower growing regions.

Pioneer Hi-Bred Production Ltd. has provided data on the identity of ExpressSun™ sunflower SU7, 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.

Agronomic characteristics such as germination, dormancy, early population, days to flowering, days to maturity, stalk lodging, root lodging, plant height, head height, stay green, yield, harvest moisture, and oil at 10% moisture of ExpressSun™ sunflower SU7 hybrids were compared with those of unmodified H. annuus hybrids.

Nutritional components of ExpressSun™ sunflower SU7 such as proximates, amino acids and fatty acids were compared with an unmodified sunflower counterpart. Levels of anti-nutritional factors were also compared between ExpressSun™ sunflower SU7 and the unmodified counterpart.

The Biotechnology Environmental Release Assessment (BERA) Unit of the Science Strategies Directorate, CFIA, has reviewed the above information, in light of the assessment criteria for determining environmental safety of PNTs, as described in the Directive 94-08 (Dir94-08), entitled "Assessment Criteria for Determining Environmental Safety of Plants With Novel Traits". The BERA Unit has considered:

  • potential of ExpressSun™ sunflower SU7 to become a weed of agriculture or to be invasive of natural habitats;
  • potential for gene-flow from ExpressSun™ sunflower SU7 to wild relatives whose hybrid offspring may become more weedy or more invasive;
  • potential for ExpressSun™ sunflower SU7 to become a plant pest;
  • potential impact of ExpressSun™ sunflower SU7 or its gene products on non-target species, including humans; and
  • potential impact of ExpressSun™ sunflower SU7 on biodiversity

The Animal Feed Division of the Animal Health Directorate, CFIA, has also reviewed the above information with respect to the assessment criteria for determining the safety and efficacy of livestock feed, as described in Directive 95-03 (Dir95-03), entitled "Guidelines for the Assessment of Novel Feeds: Plant Sources". The Animal Feed Division has considered:

  • potential impact of ExpressSun™ sunflower SU7 on livestock nutrition; and
  • potential impact of ExpressSun™ sunflower SU7 on livestock and workers/bystanders.

Pioneer Hi-Bred Production Ltd. has provided the CFIA with a method for the detection and identification of sunflower products containing ExpressSun™ sunflower SU7.

III. Description of the Novel Trait

1. Development Method

ExpressSun™ sunflower SU7 was developed by subjecting seeds of the sunflower line HA89 to the mutagenic agent ethyl methanesulfonate (EMS). The mutagenized seeds were treated with sulfonylurea herbicides to identify sulfonylurea tolerant plants. After field evaluations of several mutant lines for preferred characteristics, the SU7 mutant was selected for further breeding.

2. Sulfonylurea Tolerance

Sulfonylurea herbicides are active against the enzyme acetohydroxyacid synthase (AHAS), also known as acetolactate synthase (ALS).

AHAS is an enzyme found in bacteria, certain other micro-organisms and plants. This enzyme catalyses 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 sunflowers are not tolerant to sulfonylurea herbicides.

A single amino acid substitution in the AHAS gene, sufficient to alter the binding site such that sulfonylurea herbicides no longer binds to the AHAS enzyme, resulted in the herbicide tolerant phenotype. Pioneer Hi-Bred Production Ltd. provided data that demonstrated that ExpressSun™ sunflower SU7 possesses the same mutation as the mutation present in some sulfonylurea tolerant wild sunflower populations discovered in Kansas.

The novel sulfonylurea tolerance is under the control of the native AHAS promoter and is believed to be constitutively expressed. Sequence information for the modified AHAS gene was submitted.

The sulfonylurea tolerance of the modified AHAS enzyme was demonstrated in vitro by comparison of the activity of the AHAS enzyme extracted from ExpressSun™ sunflower SU7 plants to that of sulfonylurea-susceptible sunflower plants in presence of sulfonylurea herbicides.

AHAS proteins are not known toxins or allergens. Since the amino acid sequence of the mutated AHAS of ExpressSun™ sunflower SU7 differs by one amino acid from that of unmodified sunflowers, no changes in the allergenic or toxicological properties are anticipated for ExpressSun™ sunflower SU7 AHAS. Bioinformatic analysis confirmed the lack of homology between the amino acid sequence of ExpressSun™ sunflower SU7 AHAS and that of known or putative allergens or toxins.

ExpressSun™ sunflower SU7 is agronomically and compositionally equivalent to unmodified sunflower, indicating that it is unlikely that secondary mutations causing unintended effects have occurred in the sunflower genome.

3. Stable Expression

Segregation analyses across five generations were performed to determine the inheritance of the sulfonylurea tolerance trait. The results of the analysis are consistent with the finding of a single dominant allele that segregates according to the Mendelian laws of genetics. The mutation present in the AHAS enzyme of ExpressSun™ sunflower SU7 is therefore stable across generations.

IV. Assessment Criteria for Environmental Safety

1. Potential of ExpressSun™ Sunflower SU7 to become a Weed of Agriculture or be Invasive of Natural Habitats

Sunflower production in Canada occurs in southern Manitoba, Saskatchewan and Alberta, with a very small amount of production in Ontario. Cultivated sunflower does not have a high potential for weediness. Sunflower plants can grow as volunteers in a cultivated field following a sunflower crop and are usually eliminated via cultivation or the use of herbicides. In the recent provincial weed surveys conducted in Manitoba (2002) and Saskatchewan (2003), volunteer sunflower was ranked the 66th and 85th most abundant weed, respectively, and the Prairie Weed Survey Report 2005 ranked "Sunflower species" (Helianthus sp.) 95th out of 148 species in terms of relative abundance.

According to the information provided by Pioneer Hi-Bred Production Ltd., no competitive advantage was conferred to ExpressSun™ sunflower SU7, other than that conferred by tolerance to sulfonylurea herbicides. ExpressSun™ sunflower SU7 hybrids were tested at four locations in 2003 in the United States. A total of 12 agronomic characteristics were evaluated. These agronomic traits covered a broad range of characteristics that encompass the entire life cycle of the sunflower plant and included germination (including dormancy), early population, days to flowering, days to maturity, stalk lodging, root lodging, plant height, head height, stay green, yield, harvest moisture, oil at 10% moisture, insect damage, and disease incidence. The results showed no significant differences between ExpressSun™ sunflower SU7 hybrids and their unmodified counterparts, and support a conclusion of phenotypic equivalence to currently commercialized sunflower varieties. It is therefore not expected that ExpressSun™ sunflower SU7 would possess traits that would render it invasive of natural habitats since none of the reproductive or growth characteristics were modified.

Sulfonylurea tolerance in itself will not cause ExpressSun™ sunflower SU7 to become more weedy or invasive in managed habitats than non-modified H. annuus. Sulfonylurea-tolerant sunflower volunteers will not be controlled in subsequent crops if a Group 2 herbicide is used as the sole weed control tool. However, control of sulfonylurea tolerant sunflower as a volunteer weed in other crops or in fallow ground can readily be achieved by the use of classes of herbicides with other modes of action (i.e. non-Group 2 herbicides) or by mechanical means.

The above considerations have led the CFIA to conclude that ExpressSun™ sunflower SU7 has no ecological advantages when compared with currently commercialized sunflower varieties.

Pioneer Hi-Bred Production Ltd. provided the CFIA with a stewardship plan that describes appropriate strategies that will allow the management of ExpressSun™ sunflower SU7 volunteers, as well as other approved sunflower lines expressing sulfonylurea tolerance (see Appendix 1).

2. Potential for Gene Flow from ExpressSun™ Sunflower SU7 to Relatives Whose Hybrid Offspring May Become More Weedy or More Invasive

Helianthus annuus L. is a native of North America. Its wild relatives and other Helianthus species are distributed widely across the Central Plains of Canada from north to south. The wild H. annuus is a common roadside weed in the southern parts of the prairies, particularly in Manitoba, extending into the central United States. The cultivated and wild H. annuus have many opportunities for hybridization as they often grow in close proximity. These species overlap in flowering time and are visited by the same pollinators. Genetic cultivar markers are readily found in wild populations of H. annuus indicating no strong barrier to the introgression of domesticated germplasm into wild populations. H. petiolaris, another annual species that occurs in pockets in Canada, has also been known to hybridize with H. annuus.

Several perennial species occur in Canada. The most conspicuous is the H. maximiliani which flowers on the roadside in late summer and fall. Some H. giganteus occurs in pockets and the H. tuberosus (Jerusalem artichoke) is found primarily on riverbanks. This species has been cultivated to a small extent for its tubers. Hybridization with perennial species that are found in Canada occurs very rarely in nature. Artificial methods are required to cross H. annuus with these perennial species.

The most likely introgression of genes from cultivated H. annuus would be into wild H. annuus. The CFIA has therefore determined that gene flow from ExpressSun™ sunflower SU7 to wild sunflower in Canada is very likely. However, the sulfonylurea tolerance trait is already present at various levels in wild Canadian populations. In addition, gene flow from ExpressSun™ sunflower SU7 to wild sunflowers in Canada would not be expected to result in increased invasiveness of the offspring, as the sulfonylurea tolerance trait is not associated with enhanced weediness or any other properties. The occurrence of sulfonylurea tolerant wild sunflowers will not cause weed management issues as sulfonylurea tolerant wild sunflowers will still be easily controlled with herbicides with other modes of action (non-Group 2 herbicides) or cultivation. Pioneer Hi-Bred Production Ltd. has provided the CFIA with a stewardship plan that describes appropriate strategies that will allow the deployment of cultivated sunflower lines expressing sulfonylurea tolerance while minimizing outcrossing to wild sunflowers and volunteers (see Appendix 1). This stewardship plan also describes management strategies for the control of these plants should they appear in an agronomic situation.

Any new authorization of a PNT must take into account the spectrum of PNTs that have already been approved for unconfined environmental release in Canada. In the case of sunflower, another herbicide-tolerant sunflower has previously been authorized (DD2005-50). This sunflower is tolerant to imidazolinone herbicides (which are also Group 2 herbicides). Since there are no barriers to outcrossing between different varieties of cultivated H. annuus and wild H. annuus, there is the possibility that these two herbicide-tolerance traits could become combined in volunteer sunflower plants or in individuals in wild populations. It is not known whether these two traits co-exist in wild populations of H. annuus in Canada; however, since each trait is not expected to result in increased weediness or invasiveness on its own, the combination of traits is also not expected to result in increased weediness or invasiveness. Additionally, the stewardship plans that have been provided by Pioneer Hi-Bred Production Ltd. and BASF Canada each provide strategies for the management of volunteers or individuals in wild populations with both of these traits. These plants will still be controlled by non-Group 2 herbicides and by non-chemical methods of control that control H. annuus.

3. Altered Plant Pest Potential of ExpressSun™ Sunflower SU7

H. annuus is not a plant pest in Canada and the sulfonylurea tolerance trait in ExpressSun™ sunflower SU7 is not expected to affect its plant pest potential. The mutation of the AHAS gene in ExpressSun™ sunflower SU7 is not associated with plant pest potential. In addition, ExpressSun™ sunflower SU7 is not more susceptible to insect pests or pathogens than unmodified sunflower. The CFIA has therefore determined that ExpressSun™ sunflower SU7 does not present a plant pest concern.

4. Potential Impact of ExpressSun™ Sunflower SU7 on Non-Target Organisms

The AHAS enzyme is not a known toxin, does not confer resistance to agricultural pests and is commonly found in a wide variety of plants and micro-organisms with a history of safe use. Single amino acid modification of the AHAS enzyme, which alters the herbicide binding site on the enzyme, is the molecular basis for sulfonylurea tolerance in ExpressSun™ sunflower SU7. The mutation in the AHAS gene of ExpressSun™ sunflower SU7 is not expected to make the sunflower AHAS protein harmful to interacting organisms, including humans.

No unexpected novel traits resulting from the mutation process were detected in ExpressSun™ sunflower SU7. The agronomic, morphological and compositional characteristics of ExpressSun™ sunflower SU7 are within the range of values displayed by currently commercialized sunflower varieties, indicating that the mutation of the AHAS gene in ExpressSun™ sunflower SU7 has not affected the physiology of the plant, including its resistance to insect pests and pathogens. Therefore, no negative interactions with non-target symbiotic or consumer organisms are anticipated.

The CFIA has therefore determined that the unconfined release of ExpressSun™ sunflower SU7 will not result in altered impacts on interacting organisms, including humans, compared to current commercial sunflower hybrids.

5. Potential Impact of ExpressSun™ Sunflower SU7 on Biodiversity

ExpressSun™ sunflower SU7 has no novel phenotypic characteristics which would extend its use beyond the current geographic range of sunflower production in Canada. In addition, ExpressSun™ sunflower SU7 is not different from conventional sunflower in terms of safety to non-target organisms, weediness or plant pest potential. Sulfonylurea tolerance will not alter the ability of ExpressSun™ sunflower SU7 to persist in the Canadian environment. Cultivated sunflower outcrosses under natural conditions to wild relatives in Canada, and the transfer of the sulfonylurea tolerance trait to wild sunflower is highly likely. However, the consequences of the transfer of the sulfonylurea tolerance trait are minimal as various levels of sulfonylurea tolerance have been detected in Canadian wild sunflower populations, the novel trait does not confer any selective advantages in the absence of sulfonylurea, and sulfonylurea-tolerant wild sunflowers can be controlled by herbicides with other modes of action (non-Group 2 herbicides) and cultivation.

Canada is a centre of biodiversity for sunflower germplasm. Genetic cultivar markers are readily found in wild populations of H. annuus, indicating that gene flow into wild germplasm already occurs. There is a potential concern that the herbicide tolerance trait could be linked to other domestic traits that could make wild germplasm less ‘fit', which could then be increased in the wild population by selection with sulfonylurea herbicides. The sulfonylurea tolerance trait in ExpressSun™ sunflower SU7 is not expected to alter the weediness or invasiveness of Helianthus germplasm in Canada, nor will it alter the plant pest potential of Helianthus germplasm in Canada, either alone or in combination with the imidazolinone tolerance trait in Clearfield™ sunflower (both traits are considered to be neutral in terms of weediness). The herbicide tolerance trait(s) is not expected to increase in populations of Helianthus that are not subjected to these herbicides (i.e. most wild populations); therefore, the genetic diversity of Helianthus is not likely to change due to introgression from herbicide tolerant plants followed by selection with the herbicide for herbicide tolerance.

The CFIA has therefore concluded that the impact on biodiversity of ExpressSun™ sunflower SU7 is equivalent to that of currently commercialized sunflower varieties.

Pioneer Hi-Bred Production Ltd. has provided the CFIA with a stewardship plan that describes appropriate strategies that will allow the deployment of ExpressSun™ sunflower SU7, as well as other approved sunflower lines expressing sulfonylurea tolerance, while managing the development of Group 2 herbicide resistant weeds, outcrossing with related plants, and controlling volunteer sunflowers (see Appendix 1). The stewardship plan submitted by Pioneer Hi-Bred Production Ltd. is based on the biology of the sunflower plant and on associated agronomic practices.

The ExpressSun™ sunflower SU7 Herbicide Tolerance Stewardship Plan comprises the ExpressSun™ (Express® Tolerant) Sunflower Stewardship Plan. As part of its stewardship plan, Pioneer Hi-Bred Production Ltd. is responsible for communicating to Canadian sunflower producers the general recommendations of the ExpressSun™ Sunflower SU7 Herbicide Tolerance Stewardship Plan. A number of strategies have been developed by Pioneer Hi-Bred Production Ltd. to communicate the best management strategies to growers adopting the technology and allow them to report any problems. In addition, Pioneer Hi-Bred Production Ltd. is required to monitor grower compliance to determine the effectiveness of the stewardship plan and make any changes to the plan as appropriate.

The stewardship plans for sulfonylurea and imidazolinone herbicides include compatible management strategies for Group 2 herbicide tolerant sunflower crops, volunteers, and for gene flow to wild populations.

V. Criteria for the Livestock Feed Assessment

1. Potential Impact of ExpressSun™ Sunflower SU7 on Livestock Nutrition

Nutritional composition

The compositional equivalence of ExpressSun™ sunflower SU7 to an isogenic control was assessed from four replicated sites in the US. Whole seed, toasted meal and refined oil samples were analyzed for proximate, ADF, NDF, amino acids, fatty acids, minerals, vitamins, sugars, tocopherols and sterols. There were no statistically significant differences between ExpressSun™ sunflower SU7 and control sunflower seeds for palmitic, palmitoleic, stearic, oleic, linoleic, linolenic, arachidic, behenic, eicosenoic and tetracosanoic acid. Statistically significant differences were shown between ExpressSun™ sunflower SU7 and control seeds for crude fat and myristic acid, however, values were within literature values. Acid detergent fibre in the ExpressSun™ sunflower SU7 meal was statistically significantly higher than the control, but was within literature ranges. No significant differences were observed between ExpressSun™ sunflower SU7 and control meal for aspartic acid, glutamic acid, histidine, arginine, threonine, valine, methionine, cystine, isoleucine, leucine, and phenylalanine. Serine, glycine, alanine, proline, tyrosine, lysine and tryptophan were statistically significantly lower in ExpressSun™ sunflower SU7 meal than test meal, however the levels were within literature ranges. Except for Vitamin B2, there were no statistically significant differences between ExpressSun™ sunflower SU7 and control meal for all minerals analyzed. The statistical difference between ExpressSun™ sunflower SU7 and the control for Vitamin B2 was determined to not be biologically relevant. No statistically significant differences were observed between test and control for glucose and sucrose content. No statistically significant differences were observed between ExpressSun™ sunflower SU7 and test oil for all fatty acids, tocopherol and tocopherols. Campesterol was significantly higher in ExpressSun™ sunflower SU7 than the control but within literature values. Stigmasterol and beta-sitosterol were not significantly different between ExpressSun™ sunflower SU7 and test oil.

Antinutritional factors

Phytic acid, trypsin inhibitor and chlorogenic acid were analyzed in ExpressSun™ sunflower SU7 meal and compared to an isogenic control. No statistically significant differences were observed between ExpressSun™ sunflower SU7 band the control for chlorogenic acid and phytic acid. The levels of trypsin inhibitor were below the detection limit for the assay for both ExpressSun™ sunflower SU7 and the control meal.

The evidence provided by Pioneer Hi-Bred Production Ltd. supports the conclusion that the nutritional composition of ExpressSun™ sunflower SU7 is substantially equivalent to conventional sunflower varieties.

2. Potential Impact of ExpressSun™ Sunflower SU7 on Livestock and Workers/By-standers

The AHAS enzyme is found in a wide variety of plants and micro-organisms. AHAS is not a known toxin or allergen and a single base pair change would not be expected to change this. AHAS from ExpressSun™ sunflower SU7 is feedback inhibited as is unmodified AHAS, shows similar enzyme activity to unmodified AHAS, is heat labile and does not have homology with any known allergens or toxins. Based on the information provided by Pioneer Hi-Bred Production Ltd., the modified AHAS is unlikely to be a novel toxin or allergen.

Based on the detailed characterization provided (nutritional composition and agronomic data of the modified plant compared to an unmodified comparator) it is unlikely that secondary mutations causing unintended effects have occurred in the sunflower genome.

The evidence provided by Pioneer Hi-Bred Production Ltd. supports the conclusion that the potential impact on livestock and workers/by-standers of ExpressSun™ sunflower SU7 is equivalent to that of currently commercialized sunflower lines.

VI. New Information Requirements

If at any time, Pioneer Hi-Bred Production Ltd. becomes aware of any information regarding risk to the environment, including risk to human or animal health, that could result from release of ExpressSun™ sunflower SU7 materials in Canada or elsewhere, Pioneer Hi-Bred Production Ltd. will immediately provide such information to the CFIA. On the basis of such new information, the CFIA will re-evaluate the potential impact of ExpressSun™ sunflower SU7 on the environment, livestock and human health, and may re-evaluate its decision with respect to the livestock feed use and environmental release authorizations of ExpressSun™ sunflower SU7.

VII. Regulatory Decision

Based on the review of data and information submitted by Pioneer Hi-Bred Production Ltd., and through comparisons of ExpressSun™ sunflower SU7 with unmodified sunflower counterparts, the Biotechnology Environmental Release Assessment Unit, CFIA, has concluded that the modified gene and its corresponding novel trait do not confer to ExpressSun™ sunflower SU7 any characteristic that would result in intended or unintended significant environmental effects following unconfined release. Therefore, ExpressSun™ sunflower SU7 poses minimal risk to the environment when compared to conventional sunflower varieties.

Based on the review of data and information submitted by Pioneer Hi-Bred Production Ltd., including comparisons of ExpressSun™ sunflower SU7 with an unmodified sunflower counterpart, the Animal Feed Division of the Animal Health Directorate, CFIA, has concluded that the modified gene and its corresponding novel trait do not confer to ExpressSun™ sunflower SU7 any characteristic that would raise any concerns regarding its safety or nutritional composition. Sunflower seed meal and hulls are currently listed in Schedule IV of the Feeds Regulations and are, therefore approved for use in livestock feeds in Canada. ExpressSun™ sunflower SU7 has been assessed and found to be as safe and as nutritious as traditional sunflower varieties. ExpressSun™ sunflower SU7 and its products are considered to meet the present ingredient definitions and are approved for use as livestock feed ingredients in Canada.

Taking into account these evaluations, unconfined release into the environment and livestock feed use of ExpressSun™ sunflower SU7 are therefore authorized by the Plant Biosafety Office of the Plant Health and Biosecurity Directorate and the Animal Feed Division of the Animal Health Directorate as of January 2, 2008. Any sunflower lines derived from ExpressSun™ sunflower SU7 may also be released into the environment or used as livestock feed, provided no inter-specific crosses are performed, provided the intended uses are similar, and provided it is known based on characterization, that these plants do not display any additional novel traits and are substantially equivalent to currently grown sunflower in Canada, in terms of their potential environmental impact and livestock feed safety.

ExpressSun™ sunflower SU7 is subject to the same phytosanitary import requirements as its unmodified counterparts.

Please refer to Health Canada's Decisions on Novel Foods of corn event MIR604.for a description of the food safety assessment of ExpressSun™ sunflower SU7.

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

Animal Feed Division
Animal Health Directorate
59 Camelot Drive, Ottawa
Telephone: 613-225-2342
Facsimile: 613-773-7565

Plant Biosafety Office
Plant Health and Biosecurity Directorate
59 Camelot Drive, Ottawa
Ontario K1A 0Y9
Telephone: 613-225-2342
Facsimile: 613-773-7277

Appendix I: ExpressSun™ Sunflower SU7 Herbicide Tolerance Stewardship Plan

Introduction

The ExpressSun™ Production System for Sunflower is an innovative cropping system that offers enhanced broadleaf weed control. It provides a number of new opportunities to Canadian producers:

  • Superior post-emergence control of Canada thistle and many other annual broadleaf weeds in conventional, minimum-till or no-till sunflower production systems.
  • Another option to control weeds and manage the development of resistance.
  • High yielding sunflower hybrids from leading seed companies include the ExpressSun™ trait with built-in tolerance to tribenuron-methyl, the active ingredient in DuPont™ Express® herbicide.

The ExpressSun™ "Trait" in Sunflower

The ExpressSun™ trait for sunflowers was discovered in 1998 by DuPont™. The tolerance trait was obtained using induced mutagenesis and selection. Sunflower seeds treated with a mutagenic agent were grown into mature plants to produce second-generation seeds that were harvested. The second-generation seeds were germinated in the presence of an effective amount of a sulfonylurea herbicide to select for seeds containing a trait conferring tolerance to tribenuron-methyl herbicide. The surviving germinated seeds were grown into mature plants and self-pollinated to produce seeds containing the heritable tolerance trait. The herbicide tolerant trait was maintained through several backcross generations. This ExpressSun™ trait was incorporated into cultivated germplasm via traditional plant breeding techniques.

ExpressSun™ sunflower hybrids are not commercially cross-tolerant to all Group 2 herbicides. This group includes the sulfonylurea, imidazolinone, triazolopyrimidine, pyrimidinyl(thio) benzoate, and sulfonylaminocarbonyl-triazolinone herbicides. Application of Group 2 herbicides other than tribenuron-methyl to ExpressSun™ sunflower hybrids may cause injury; however, acceptable control of volunteers or wild sunflowers may not be achieved with Group 2 herbicides.

Key Sustainability Issues

Development of Resistance

The Herbicide Resistance Action Committee (HRAC) is an industry initiative which fosters co-operation between plant protection manufacturers, government, researchers, advisors and farmers. The objective of the working group is to facilitate the effective management of herbicide resistance. HRAC has identified a number of factors to consider when evaluating herbicide resistance risk. The most important factors influencing a plant's potential to develop resistance are:

Biology and genetic make up of the weed species in question

Number or density of weeds: As resistant plants are assumed to be present in all natural weed populations, the higher the density of weeds, the higher the chance that some resistant individuals will be present.

Natural frequency of resistant plants in the population: Some weed species have a higher propensity toward resistance development; this relates to genetic diversity within the species and, in practical terms, refers to the frequency of resistant individuals within the natural population.

Seed soil dormancy potential: Plant species with longer soil dormancy will tend to exhibit a slower resistance development under a selection pressure as the germination of new, susceptible plants will tend to dilute the resistant population.

Crop management practices which may enhance resistance development

Frequent use of herbicides with a similar mode of action: The combination of ‘frequent use' and ‘similar mode of action' is the single most important factor in the development of herbicide resistance.

Cropping rotations with reliance primarily on herbicides for weed control: The crop rotation is important in that it will determine the frequency and type of herbicide to be applied. It is also the major factor in the selection of non-chemical weed control options. Additionally, the cropping period for the various crops will have a strong impact on the weed flora present.

Lack of non-chemical weed control practices: Cultural or non-chemical weed control techniques incorporated into an integrated approach is essential to the development of a sustainable crop management system, as these non-chemical control options introduce new methods which may help delay the development of weed resistance, as these non-chemical control options introduce new methods which may help delay the development of weed resistance or shifts in weed populations.

Identifying Weed Resistance

Failure to achieve expected weed control levels does not, in most cases, mean that a farmer has encountered resistance. A full analysis of the herbicide application, rate of use, weed type and stage of growth, climatic conditions and agronomic practice should be reviewed.

If, after the initial investigation, resistance is still suspected, then consideration of historical information may point to factors leading to resistance development. The following questions are recommended;

  • Has the same herbicide or herbicides with the same mode of action been used in the same field or in the general area for several years?
  • Has the uncontrolled species been successfully controlled in the past by the herbicide in question or by the current treatment?
  • Has a decline in the control been noticed in recent years?
  • Are there known cases of resistant weeds in adjacent fields, farms, roadsides, etc.?
  • Is the level of weed control generally good on the other susceptible species except the ones not controlled?

If the answer to any of these questions is 'yes' and all other factors have been ruled out, then resistance should be strongly suspected. Steps should then be taken to collect a sample of whole plant or seed from the suspected resistant weed population for a resistance confirmation test. Contact your local DuPont™ representative for further information (www.dupont.ca/ag) or email (ag.hotline@can.dupont.com) or call our Toll-Free Hotline: 1-800-667-3925.

Weed Resistance Management

Herbicides have been grouped based on their mode of action. Herbicides that are in Group 2 are those classed as ALS/AHAS inhibitors. DuPont™ markets herbicides that are in the sulfonylurea chemical family and they are members of Group 2. The only herbicides that can be used in the ExpressSun™ production system is DuPont™ Express® herbicide. DuPont™ is committed to maintaining the efficacy of all of our herbicides in order to provide growers with effective, high performance, environmentally sound products for many years.

The key to the performance of ExpressSun™ Production Systems is effective weed resistance management. DuPont™ is committed to delivering sustainable cropping systems that incorporate best practice principles.

Following is a discussion and proposed strategies for managing ALS herbicide resistance in weed populations under the ExpressSun™ Production System. The guidelines for managing the development of weed resistance presented here are consistent with recommendations put forward by HRAC.

DuPont™ will implement a stewardship plan for ExpressSun™ sunflower hybrids that will include educating sales staff and growers on the best management practices that are intended to decrease and delay the incidence of herbicide resistant sunflower volunteers, gene flow to wild relatives of sunflower, and selection of herbicide resistant weeds.

Stewardship practices for ExpressSun™ Sunflower Hybrids

To preserve the efficacy of Express® herbicide, producers will be required to follow specific management practices designed to prevent or delay herbicide resistance in wild species of sunflower. These practices may also help to delay the development of resistance to this herbicide in other weed species. These practices span across crops to promote herbicide resistance management and should include the following:

  • Use non-ALS (non-Group 2) mode of action herbicides in a tank-mix with ALS herbicides or as sequential treatments in the rotational crop that will control wild or volunteer sunflower.
  • Control wild sunflower in farmed and non-crop areas adjacent to ExpressSun™ sunflower hybrid fields through the use of non-ALS herbicides and/or mowing prior to seed set.
  • Control emerged wild sunflower prior to planting ExpressSun™ sunflower hybrids with tillage or by utilizing non-ALS burn down herbicides, or use ALS burn down herbicides in a tank-mix with non-ALS herbicides that will provide control of sunflower.
  • As practical, use ALS herbicides in a tank-mix with non-ALS (non-Group 2) modes of action herbicides or use ALS herbicides in a sequential program with alternate mode of action herbicides that control wild and volunteer sunflower.
  • Follow an Integrated Weed Management (IWM) program that includes herbicides, cultural practices and crop rotations in order to manage weed populations and minimize weed seed development
  • Always grow ExpressSun® sunflower hybrids in rotation with other crops as part of a multi-year rotation, for example wheat/corn/soybean. Do not plant Express® herbicide tolerant sunflower hybrids on land with a history of heavy infestation of wild sunflower.
    1. Stewardship and resistant weed management and understanding are essential to preserving this technology. Good stewardship should be incorporated into all marketing, positioning, promotion and communications strategy, with training and education of all parties who touch this technology.
    2. Prior to the beginning of each marketing year, Licensee shall provide copies of all communications and training material to DuPont™ approval to make sure proper stewardship and weed resistance is being managed with training and monitoring plans aligned with HRAC principals
    3. Resistance Management through grower mailings. To preserve and extend the life of this technology, after planting and prior to spraying in the year of seed purchase Licensee shall contact each customer and remind them of his/her responsibilities regarding stewardship and specific agronomic practices. The following year prior to planting Licensee shall send each customer a mailing reminding him/her of their stewardship responsibilities and weed resistance management practices in rotational crops

These guidelines form the basis for our stewardship plans for crops grown using the ExpressSun™ Production System. In addition licensee shall also follow and align with Herbicide Resistance Action Committee (HRAC) guidelines. These guidelines include the elements outlined below.

HRAC Guidelines for the Prevention and Management of Herbicide Resistance

The prevention of resistance occurring is an easier and cheaper option than managing a confirmed resistance situation. Experience has shown that simply changing herbicides is not enough to overcome resistance in the mid to long term and that a sustainable, integrated system needs to be developed which is appropriate for the farm in question.

Integrated Weed Management is defined as the use of a range of control techniques, embracing physical, chemical and biological methods in an integrated fashion without excessive reliance on any one method (Powles and Matthews, 1992).

The following information outlines the three key areas of weed management; Crop rotation management, Cultural techniques and Chemical tools which, when employed in a rotational and integrated approach will help to reduce the selection pressure on any weed species – hence significantly reducing the chance of survival of resistant weeds.

Rotation of Crops

The principle of crop rotation as a resistance management tool is to avoid successive crops in the same field which require herbicides with the same mode of action for control of the same weed species. Crop rotation allows the following options:

  • Different crops will allow rotation of herbicides having a different mode of action
  • The growth season of the weed can be avoided or disrupted
  • Crops with differing sowing times and different seedbed preparation can lead to a variety of cultural techniques being employed to manage a particular weed problem.
  • Crops also differ in their inherent competitiveness against weeds. A strongly competitive crop will have a better chance to restrict weed seed production.
Cultural Techniques

Cultural (or non-chemical) weed control methods do not exert a chemical selection pressure and assist greatly in reducing the soil seed bank. Cultural techniques must be incorporated into the general agronomy of the crop and other weed control strategies. Some of the cultural measures for weed control could include:

  • Cultivation or ploughing prior to sowing to control emerged plants and to bury non-germinated seed
  • Delaying planting so that initial weed flushes can be controlled with a non-selective herbicide
  • Using certified crop seed free of weed
  • Stubble burning, where allowed, can limit weed seed fertility.
Herbicide Rotation and Herbicide Mixtures

Herbicide rotation or mixtures refers to the rotation or mixtures of Herbicide Mode of Action against any identified weed species. When planning a weed control program, products should be chosen from different mode of action groups to control the same weed either in successive applications or in mixtures.

A general guideline for the rotation of chemical groups should consider:

  • Avoid continued use of the same herbicide or herbicides having the same mode of action in the same field unless it is integrated with other weed control practices
  • Limit the number of applications of a single herbicide or herbicides having the same mode of action in a single growing season
  • Where possible, use mixtures or sequential treatments of herbicides having a different mode of action but which are active on the same target weeds
  • Use non-selective herbicides to control early flushes of weeds (prior to crop emergence) and/or weed escapes
The Use of Herbicide Mixtures to Prevent Resistance

Mixtures can be a useful tool in managing or preventing the establishment of resistant weeds.

For chemical mixtures to be effective, they should:

  • include active ingredients which both give high levels of control of the target weed, AND
  • include active ingredients from different mode of action groupings.

The HRAC classification of herbicides according to mode of action is in itself NOT a recommendation of which herbicide to use. The system is not based on resistance risk assessment but solely chemical mode of action. The guide is designed to be used as a tool to select herbicides from different mode of action groups so that appropriate mixtures or rotations can be planned within an integrated weed management system. Additional to the above guideline, the grower should;

  • Know which weeds infest his field or non-crop area and where possible, tailor his weed control program according to weed densities and/or economic thresholds
  • Follow label use instructions carefully. This especially includes recommended use rates and application timing for the weeds to be controlled
  • Routinely monitor results of herbicide applications, being aware of any trends or changes in the weed populations present
  • Maintain detailed field records so that cropping and herbicide history is known

Integrated Weed Management (IWM) in ExpressSun™ sunflower hybrids

ExpressSun™ sunflower hybrids are tolerant to the tribenuron-methyl, which is a Group 2 herbicide. Group 2 herbicides work by inhibiting acetolactate synthase, an enzyme that is required for the production of the amino acids leucine, isoleucine and valine in plants. Group 2 herbicides are known as 'ALS inhibitors'.

Continuous use of Group 2 herbicides may result in the selection of weed biotypes with a resistance to this group of herbicides. Preservation of the effectiveness of this group of herbicides is vital for efficient and cost-effective agricultural production in Canada.

The production of other crops allows for the use of alternate mode of action herbicides and tillage, where appropriate, to delay the development of herbicide resistance. Proper crop rotation promotes good agronomics by reducing disease and insect pressure in sunflower; producers of ExpressSun™ sunflower hybrids should follow recommended crop rotation practices.

Use alternate (non-Group 2) mode of action herbicides with activity on sunflower in the rotational crops. This includes herbicides that are classed as growth regulators or photosynthetic inhibitors. This reduces the selection pressure from continuous dependence on ALS inhibiting herbicides. It provides an alternative mode of action to control volunteer sunflowers that may be present. Some alternative herbicides are listed in the "Controlling volunteers from ExpressSun™ sunflower" section of this stewardship plan.

Where possible, use sequential applications of partner herbicides or tank mix herbicides with multiple modes of action on target weed species. Consideration should be given to less frequent use of Group 2 herbicides (e.g. limiting applications of Group 2 herbicides to one application per growing season) to delay the onset of resistance development. This includes the use of Group 2 herbicides both within the ExpressSun™ sunflower hybrids and in conventional crops.

Do not plant ExpressSun™ sunflower hybrids on cropland or near road ditches, field borders, fence rows etc. with a history of heavy infestations of wild sunflower. This will help minimize the potential of cross-pollination of wild type sunflowers with ExpressSun™ sunflower hybrids.

Control wild sunflower in areas around ExpressSun™ sunflower hybrid fields (road ditches, field borders, fence rows) through the use of non-Group 2 herbicides and/or mowing prior to seed set. DO NOT plant ExpressSun™ sunflower hybrids if the area adjacent to the field has a heavy infestation of wild sunflower. Avoid cultural practices that would result in cross-pollination of wild type sunflowers with ExpressSun™ sunflower hybrids (see the "Managing Outcrossing" section for additional information).

Controlling Volunteers from ExpressSun™ Sunflower

Control of volunteer plants of the same crop species is important to prevent herbicide tolerance from spreading to wild relatives. Also, volunteer plants can become weeds in crops other than sunflowers

ExpressSun™ sunflowers will be controlled by all herbicides currently registered for control of sunflower, with the possible exception of Group 2 herbicides (a possibility of a low level of cross-tolerance to other Group 2 herbicides may result in an unacceptable level of control).

ExpressSun™ Sunflower volunteers will be controlled by glyphosate, and a range of herbicides registered for use in wheat, barley, and other crops.

Controlling Volunteer Sunflowers

Prevention is the best means of achieving control of volunteer sunflowers. Special attention should be given to minimizing seed loss during harvest by not delaying harvests (harvest before seed drop occurs), properly cleaning and maintaining harvesting equipment and grain handling facilities (remove all seed when cleaning and handling, and calibrating equipment so that loss is minimized during harvest).

In addition, all volunteers should be controlled in the season following cultivation of an ExpressSun™ hybrid. Volunteers should be controlled prior to crop seeding by cultural and chemical (preplant burndown non-Group 2 herbicides) methods. Volunteers should also be controlled in following crops with non-Group 2 herbicides prior to flowering of the volunteers. Crop rotation is also an effective means of controlling volunteer sunflowers. In Canada sunflowers are commonly rotated with cereal crops. There are a variety of non-Group 2 herbicides available in cereal crops that will control volunteer sunflowers. Some of these are listed as follows; additional information may be found in provincial guides to weed control:

  • Bromoxynil (Group 6)
  • 2,4-D amine or ester (Group 4)
  • MCPA amine or ester (Group 4)
  • Fluroxypyr (Group 4)
  • Mecoprop (Group 4)
  • Clopyralid (Group 4)
  • Dicamba (Group 4)

There are other non-Group 2 herbicides available and the label can be consulted to determine their suitability for use on volunteer sunflowers. Consult local herbicide labels for use rates and application practices.

Potential for Introgression from ExpressSun™ Sunflowers into Relatives (Crops and Weeds)

Miller and Seiler, 2005 determined that resistance to tribenuron-methyl was found in accessions of Helianthus annuus collected in the three provinces of Canada, Alberta, Saskatchewan, and Manitoba. No resistance was found in the Helianthus petiolaris accessions. Of the H. annuus accessions tested (23), 12 accessions, or 52% had resistant plants. These findings were very similar to those reported by Olsen et. al, 2004 who found 57% of wild accessions collected in the United States had resistant plants. Within the 12 accessions found to have resistance, the highest percentage of resistant plants in an accession was 5.9%. This accession, PI 592307, was collected near Welling, Alberta, from the margin of a wheat field. The average resistance found in plants tested of the 12 accessions was 3.4%.

The investigators who conducted this survey concluded that tribenuron resistance occurs in wild sunflower and this resistance is widespread among accessions collected across the provinces of Canada, that resistance occurred in low frequencies in those accessions, and the resistance occurred in the environment before release of Express® tolerant sunflower hybrids for commercial production in Canada.

However, it is still important to minimize gene flow between ExpressSun™ hybrids and wild sunflower species, as the specific mechanism(s) of resistance in the wild populations was not determined in these studies. Gene flow from ExpressSun™ into wild populations may therefore add additional resistance mechanisms into the wild sunflower gene pool, and steps should be taken to minimize it.

Managing Out-crossing of ExpressSun™ Sunflowers to Related Species

Many of the weed management practices listed in the HRAC guidelines (see above) to delay the development of weed resistance and for controlling ExpressSun™ sunflower volunteers will be effective in minimizing the impact of outcrossing. These include:

  1. Rotation of crops
  2. Cultural (or non-chemical) weed control methods
  3. Herbicide rotation to non-Group 2 herbicide(s)
  4. The use of herbicide mixtures to prevent resistance (if a Group 2 herbicide is used, a non-Group 2 herbicide with the same activity and persistence on sunflower should be included)
  5. Maintaining detailed field records so that cropping and herbicide history is known
  6. Control all volunteers in the season after growing ExpressSun™ Sunflowers. (Refer to earlier section, Controlling Volunteers with ExpressSun™ Technology).
  7. Follow the recommended crop rotation practices for sunflower when growing ExpressSun™ sunflower.
  8. Use alternate (non-Group 2) mode of action herbicides with activity on sunflower in the rotational crops.
  9. Do not plant ExpressSun™ sunflowers on cropland or near road ditches, field borders, fence rows etc. with a history of heavy infestations of wild sunflower.
  10. When possible, control wild sunflower in areas around ExpressSun™ sunflower fields (road ditches, field borders, fence rows) through the use of non-Group 2 herbicides and/or mowing prior to seed set.
  11. DO NOT plant ExpressSun™ sunflower if the area adjacent to the field has a heavy infestation of wild sunflower, or if you cannot control the wild sunflower population.
  12. Control emerged wild sunflower prior to planting ExpressSun™ sunflowers. Utilize non-Group 2 burndown herbicides in no-till or min-till situations, or tillage in conventional-till systems.

Communication and monitoring of the Best Management Practice Program for the ExpressSun™ Sunflower Production System

DuPont™ intends to communicate the stewardship plan to producers through both broad-based and targeted approaches. Broad-based communications include: Technical bulletins, Business Representative presentations, grower mailings and the DuPont™ Crop Protection internet web-site. To preserve and extend the life of this technology, after planting and prior to spraying in the year of seed purchase Licensee shall contact each customer and remind them of his/her responsibilities regarding stewardship and specific agronomic practices. The following year prior to planting Licensee shall send each customer a mailing reminding him/her of their stewardship responsibilities and weed resistance management practices in rotational crops. DuPont™ will track and respond to any reported incidents of suspected weed resistance. Growers can contact DuPont™ at call our Toll-Free Hotline: 1-800-667-3925.

References

Arias, D.M. and L.H. Rieseberg. 1994. Gene flow between cultivated and wild sunflowers. Theor. Appl. Genet. 89:655-660.

Burke, J.M., K.A. Gardner and L.H. Rieseberg. 2002. The potential for gene flow between cultivated and wild sunflower (Helianthus annuus) in the United States. Amer. J. Bot. 89(9): 1550-1552.

Heiser, C. B., Jr. Taxonomy of Helianthus and Origin of Domesticated Sunflower. 1978 In: Sunflower Science and Technology. Agron. 19. pp. 31-53. Ed. Carter, J. F.

Linder, C.R., I. Taha, G.J. Seiler, A.A. Snow, and L.H. Rieseberg. 1998. Long-term introgression of crop genes into wild sunflower populations. Theor. Appl. Genet. 96:339-347

Miller, J.F., Seiler, G.J. 2005. Tribenuron Resistance In Accessions Of Wild Sunflower Collected In Canada. Proceedings Sunflower Research Workshop.

Olson, B. L. S., K. Al-Khatib, and R. M. Aiken. 2004. Distribution of resistance to imazamox and tribenuron-methyl in native sunflower. www.sunflowernsa.com/research/research-workshop/documents/158.pdf

Rogers, C.E., T.E. Thompson, and G.J. Seiler. 1982. Sunflower species of the United States. Bismarck, ND: National Sunflower Association. 75 p.

Sieler, G.J. and L.H. Rieseberg. 1997. Systematics, origin and germplasm resources of the wild and domesticated sunflower. Pages 21-65 in A.A.

Schneiter, ed. Sunflower Technology and Production. Agron. Monogr. 35. Madison, WI: ASA, CSSA, and SSSA.

Snow, A.A., P. Moran-Palma. L.H. Rieseberg, A. Wszelaki and G.J. Seiler. 1998. Fecundity, phenology, and seed dormancy of F1 wild-crop hybrids in sunflower (Helianthus annuus, Asteraceae). Amer. J. Bot. 85(6): 794-801.

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

Plant Biosafety Office
Plant Health and Biosecurity Directorate
59 Camelot Drive
Ottawa, Ontario K1A 0Y9
Telephone: 613-225-2342

Animal Feed Division
Animal Health Directorate
59 Camelot Drive
Ottawa, Ontario K1A 0Y9
Telephone: 613-225-2342

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