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Clearfield Durum Wheat Varieties with an Als2 or Als3 Imidazolinone Tolerance Trait

Health Canada has notified BASF Canada Inc. that it has no objection to the food use of durum wheat varieties (DW1 and DW12) with Als2 and Als3 imidazolinone tolerance traits respectively. The Department conducted a comprehensive assessment of these varieties according to its Guidelines for the Safety Assessment of Novel Foods. These Guidelines are based upon internationally accepted principles for establishing the safety of foods with novel traits.

Background:

The following provides a summary of the notification from BASF Canada Inc. and the evaluation by Heath Canada and contains no confidential business information.

1. Introduction

The imidazolinone tolerance trait in durum wheat varieties DW1 and DW12 was introduced through chemical mutagenesis of seed and traditional breeding. Exposure to a chemical mutagen causes a genetic change that results in an alteration to the acetohydroxyacid synthase (AHAS) protein produced by the Als2 gene in DW1 and by the Als3 gene in DW12. These changes cause these plants to grow in the presence of imidazolinone herbicides. Health Canada has previously indicated no objection to the sale of imidazolinone tolerant corn (XI-12), canola (NS738, NS1471, NS1473) , rice (CL121, CL141,CFX51, and PWC16), lentils (RH44), sunflower (X81359) and wheat (AP602CL, AP205CL, Teal11A, BW 255-2 and BW238-3) in the Canadian marketplace.

The assessment conducted by Food Directorate evaluators determined how Clearfield durum wheat varieties DW1 and DW12 were developed; how their composition and nutritional quality compares to traditional durum wheats; and the potential for the presence of any toxicants, anti-nutrients, or allergens. BASF has provided data which demonstrates that Clearfield durum wheat varieties DW1 and DW12 are as safe and nutritious as the conventional durum wheat varieties sold in Canada.

The Food Program has a legislated responsibility for pre-market assessment of novel foods and novel food ingredients as detailed in the Food and Drug Regulations (Division 28). Food use of durum wheat varieties DW1 and DW12 is considered a novel food under the following part of the definition of novel foods: "c) a food that is derived from a plant, animal or microorganism that has been genetically modified such that

  1. the plant, animal or microorganism exhibits characteristics that were not previously observed in that plant, animal or microorganism."

2. Development of the Modified Plant

Imidazolinone tolerant wheat varieties DW1 and DW12 were developed using seed mutagenesis with ethyl methanesulfate (EMS) and sodium azide from a parental hard amber durum wheat. These seeds were grown as the M1 generation to produce M2 generation seeds. The M2 generation and each subsequent generation until M6 where screened using imazamox for herbicide tolerance. This process has been described by the petitioner and is similar to those used in previously approved Clearfield products. Currently the DW1 and DW12 varieties are of the M8 generation.

The target of the imidazolinone class of herbicides is the enzyme AHAS which is responsible for the first step in the biosynthesis of essential branched chain amino acids. The mutation which results in the tolerance to imidazolinone herbicides in both DW1 and DW12 is a single base substitution in an Als gene. For the durum variety DW1 this substitution occurs in Als 2 , for DW12 the mutation occurs in Als 3. These base substitutions result in a single amino acid change in the AHAS protein, which confers herbicide tolerance. The single amino acid change alters the binding site for the herbicide on the AHAS enzyme expressed by these Als genes while having no effect on the normal functioning of the enzyme. These mutations are equivalent to those seen in corn line XI-12 (letter of no objection issued June 8, 1998) and bread wheats SWP965001 (letter of no objection issued November 12, 1999), AP205CL (letter of no objection issued June 11, 2004), AP602CL (letter of no objection issued March 21, 2003), Teal 11A (letter of no objection issued June 25, 2004), BW238-3 and BW255-2 (both issued a letter of no objection )

3. Characterization of the Modified Plant

In both these durum wheat lines the locus of the mutation has been shown using sequencing techniques. Using cloned Als 2 and Als 3 from both DW1 and DW12, sequencing data confirmed that in durum line DW1 the mutation occurs in Als 2 with no change to the Als 3 region and in the DW12 line the mutation occurs in Als 3 with no alteration to Als 2. Sequence data from this study has also been used by the petitioner as evidence that there is a single point mutation in the coding regions of both DW1 and DW12. This single base change results in the single amino acid change that confers herbicide tolerance.

The AHAS enzyme produced by these lines have been shown to have similar activity to that produced by the wild type parent line. The mutation in the Als 2 and Als 3 genes have been shown to be stably inherited in DW1 and DW12 respectively. This has been shown through consistent tolerance to imidazolinone herbicides in generations M1 to M6 and through sequencing data generated from the M5 and M6 generations.

4. Product Information

Durum wheat varieties DW1 and DW12 differ from their traditional counterparts in that they are tolerant to Imidazolinone herbicides. This is due to a mutation in the AHAS enzyme produced by Als. A mutation in the AHAS enzyme in wheat could affect the biosynthesis of the essential amino acids isoleucine, leucine, and valine. The amino acid composition of Clearfield Durum wheat varieties DW1 and DW12 was compared to their parent, confirming that the AHAS activity of the imidazolinone-tolerant wheat was not affected by the mutation.

5. Dietary Exposure

Durum wheat varieties DW1 and DW12 are expected to be used in similar application as traditional wheat varieties by the food industry.

6. Nutrition

Nutrient and antinutrient composition of grain samples of the test varieties (DW1 and DW12) and parental control (Utopia) grown in two locations in California in 2003 and three locations in North Dakota in 2004 was determined. In addition, for comparison, composition of ten conventional durum wheat varieties grown in the same field trials in 2003, and in other North Dakota locations and in Saskatchewan, Canada, in 2004, was reported.

The components analysed included proximates (moisture, crude fat, protein and crude fiber), 18 amino acids, 33 fatty acids, 7 minerals (phosphorus, zinc, magnesium, iron, copper, manganese and potassium), 7 vitamins (thiamin/B1, niacin, pantothenic acid, pyridoxine/B6, vitamin E, vitamin B2 and folic acid), and the antinutrients phytic acid and trypsin inhibitor.

There were very few statistically significant differences between the control and test varieties. (crude fiber, fatty acids, potassium, vitamin B1 and folic acid). For these nutrients, these differences were observed only during one period (2003 field trial or 2004 field trial), were not consistent (only one of the test varieties was different from control) or in some cases, differences were in the opposite direction in 2003 compared to 2004. Consequently, it was concluded that these differences could be considered not nutritionally significant. As well, the levels of nutrients and antinutrients in DW1 and DW12 were comparable to the levels in the ten other conventional durum wheat varieties.

7. Chemistry/Toxicology

The weight of evidence suggests that the mutant AHAS from DW1 and DW12 durum wheat is unlikely to demonstrate toxic or allergenic properties under usual conditions of consumption. This conclusion is based on the observations that the protein is expressed in extremely low amounts in the edible part of the wheat, its activity is heat-labile and would be denatured during normal food preparation processes, and the protein is as sensitive to degradation in a simulated human gastrointestinal tract by trypsin as the native protein. Consequently, systemic exposure to the active AHAS protein was considered negligible. In addition, it does not share characteristics of a food allergen to a greater extent than the native protein.

The mutant AHAS protein is not homologous with any known toxins or allergens. Further, the mutant DW1 and DW1 durum wheat varieties do not express any new major proteins or altered amounts of other proteins, including endogenous wheat allergens.

CONCLUSION:

Health Canada's review of the information presented in support of the food use of imidazolinone tolerant durum wheat varieties DW1 and DW12 does not raise concerns related to food safety. Health Canada is of the opinion that food derived from Durum wheat varieties DW1 and DW12 is as safe and nutritious as food from current commercial rice varieties.

Health Canada's opinion deals only with the food use of imidazolinone tolerant Durum wheat varieties DW1 and DW12. Issues related to its use as animal feed have been addressed separately through existing regulatory processes in the Canadian Food Inspection Agency.


This Novel Food Information document has been prepared to summarize the opinion regarding the subject product provided by the Food Directorate, Health Products and Food Branch, Health Canada. This opinion is based upon the comprehensive review of information submitted by the petitioner according to the Guidelines for the Safety Assessment of Novel Foods.

(Également disponible en français)

For further information, please contact:

Novel Foods Section
Food Directorate
Health Products and Food Branch
Health Canada
Tunney's Pasture
Ottawa, Ontario K1A 0L2
Telephone: (613) 941-5535
Facsimile: (613) 952-6400

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