Novel food information: Clearfield™ bread wheat varieties with an Als3 imidazolinone tolerance trait

On this page:


Health Canada has notified BASF Canada Inc. that it has no objection to the food use of Bread wheat varieties (BW255-2 and BW238-3) with an Als3 imidazolinone tolerance trait. The Department conducted a comprehensive assessment of these varieties according to its Guidelines for the Safety Assessment of Novel Foods (September 1994). These Guidelines are based upon internationally accepted principles for establishing the safety of foods with novel traits.

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


BASF Canada developed Clearfield™ bread wheat varieties BW255-2 and BW238-3 tolerant to imidazolinone herbicides by chemical mutagenesis of seed and traditional breeding. Exposure to the chemical mutagen causes a genetic change that results in an alteration to the AHAS protein produced by the Als3 gene. This change causes the plant 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) in the Canadian marketplace.

The assessment conducted by Food Directorate evaluators determined how Clearfield™ bread wheat varieties BW255-2 and BW238-3 were developed; how their composition and nutritional quality compares to traditional bread wheats; and the potential for the presence of any toxicants, anti-nutrients, or allergens. BASF has provided data which demonstrates that Clearfield™ bread wheat varieties BW255-2 and BW238-3 are as safe and nutritious as the conventional bread wheat varieties sold in Canada.

The Food Directorate has a legislated responsibility for pre-market assessment of novel foods and novel food ingredients as detailed in Division 28 of Part B of the Food and Drug Regulations (Novel Foods). Foods derived from bread wheat varieties BW255-2 and BW238-3 are considered novel foods 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."

Development of the modified plant

The petitioner has provided information describing the process used in developing the novel bread wheat varieties BW255-2 and BW238-3. Seed from red spring wheat cultivars BW255 and BW238 were modified using mutagenesis with sodium azide, producing the M1 generation. These seeds were grown under greenhouse conditions to produce M2 and the subsequent M3 generations. Plants were selected from the M3 generation based on parental type and imidazolinone tolerance. Seeds from these plants were then used for generational increase; both varieties are currently in the M9 generation. This process has been described by the petitioner and is similar to those used in previously approved Clearfield™ wheat submissions.

The target of the imidazolinone class of herbicides is the enzyme acetohydroxyacid synthase (AHAS) which is responsible for the first step in the biosynthesis of essential branched chain amino acids. Imidazolinone tolerance in Clearfield™ Bread Wheat varieties BW255-2 and BW238-3 is due to a point mutation of a single nucleotide in the Als 3 gene. This results in a single amino acid substitution in the expressed AHAS enzyme. The single amino acid change alters the binding site for the herbicide on the AHAS enzyme expressed by Als gene while having no effect on the normal functioning of the enzyme. This mutation is similar to the mutations seen in previously approved Clearfield™ Wheat varieties.

Characterization of the modified plant

The petitioner provided sequencing data that characterized the nucleotide change, showing a single base change in the Als 3 gene resulting in a single amino acid change in the AHAS enzyme. The petitioner has also indicated that sequencing of the Als 1 and Als 2 genes shows that they are no different than wild-type wheat. Segregation data has been provided from the M3 generation showing that this trait is inherited in Mendelian fashion. At the M3 generation the petitioner has stated that plants were segregated based on zygosity and that generational increases after the M3 generation have been conducted from the homozygous population. The petitioner also provided data to show that no change in the tolerance to imidazolinone herbicides has been observed over the generations indicating that the trait is stable in the plant genome.

The petitioner provided information regarding the functionality of the mutant AHAS protein as compared to this wild type counterpart. Data from these studies indicate that the mutant protein is not significantly different in trypsin or heat sensitivity and exhibits similar feedback inhibition to the wild type.

Product information

Bread wheat varieties BW255-2 and BW 238-3 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 Als3. 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™ wheat varieties BW255-2 and BW 238-3 was compared to their respective parents, confirming that the AHAS activity of the imidazolinone-tolerant wheat was not affected by the mutation.

Dietary exposure

BW255-2 and BW238-3 wheat varieties are expected to be used in similar applications as traditional wheat varieties by the food industry.


A significant amount of nutrient and antinutrient data was provided to the Food Directorate for the evaluation of BW255-2 and BW238-3. To obtain the compositional data, a randomized complete block design was used. Grain samples were collected from the wheat varieties, BW255-2 and BW238-3, and their respective parents, BW255 and BW238. The test and control wheat were grown at three field sites in the United States, with three replications at each site, and samples representing each test and control group were collected from each replication. Samples were analyzed for proximates (moisture, crude fat, protein and crude fibre), 18 amino acids, 2 antinutrients ( phytic acid and trypsin inhibitor), 33 fatty acids ( of which five were present at levels above the detection limit, 0.011%), 7 minerals (phosphorus, zinc, magnesium, iron, copper, manganese and potassium), and 7 vitamins (thiamine, niacin, pantothenic acid, pyridoxine, total tocopherols, vitamin B2 and folic acid). Compositional data for up to 29 conventional wheat varieties were obtained using a database of grain composition of wheat varieties that was generated by BASF from grain analyses of conventional bread wheat varieties grown in replicated field trials. These data were provided for all of the nutrients and antinutrients that were analyzed in the two Als3 wheat varieties, with the exception of trypsin inhibitor which is not a significant antinutrient in wheat.

The compositional data provided by the petitioner for these two Als3 wheat varieties are acceptable, i.e. they have been obtained using an acceptable study design, and valid sampling, analytical and statistical methodologies. The data demonstrated that the levels of nutrients and antinutrients in wheat grain from BW255-2 and BW238-3 were comparable with levels in wheat grain from the parental varieties BW255 and BW238, and various conventional wheat varieties. Any statistically significant differences that did occur between the two Als3 wheat varieties and their corresponding parent varieties were not considered biologically significant.


The weight of evidence suggests that the mutant AHAS from BW255-2 and W238-3 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 the 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 BW255-2 and BW238-3 bread wheat varieties do not express any new major proteins or altered amounts of other proteins, including endogenous wheat allergens.

In conclusion, no additional health concern would be expected to be associated with the consumption of imidazolinone tolerant mutant BW255-2 and BW238-3 wheat compared with their respective parents BW255 and BW238.


Health Canada's review of the information presented in support of the food use of imidazolinone tolerant bread wheat varieties BW255-2 and BW238-3 does not raise concerns related to food safety. Health Canada is of the opinion that food derived from bread wheat varieties BW255-2 and BW238-3 is as safe and nutritious as food from current commercial bread wheat varieties.

Health Canada's opinion deals only with the food use of imidazolinone tolerant bread wheat varieties BW255-2 and BW238-3. 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 (September 1994).

For further information, please contact:

Novel Foods Section
Food Directorate
Health Products and Food Branch
Health Canada, PL2204A1
251 Frederick Banting Driveway
Ottawa, Ontario K1A 0K9

Page details

Date modified: