ARCHIVED - Imidazolinone Tolerant Rice (PWC16)

Novel Food Information - Food Biotechnology

Health Canada has notified BASF that it has no objection to the food use of grain from the Oryza sativa line PWC16 and its derivatives (CLEARFIELD, or CL rice) developed through mutation breeding, which are tolerant to imidazolinone herbicides. The Department conducted a comprehensive assessment of this rice 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.


The following provides a summary regarding the BASF notification to Health Canada and contains no confidential business information.

1. Introduction

BASF developed a rice that is tolerant to imidazolinone herbicides through a combination of mutagenesis and conventional breeding. The mutation responsible for imidazolinone tolerance is due to a point mutation of a single nucleotide in the acetohydroxyacid synthase (AHAS) gene, similar to that previously described for imidazolinone tolerant corn, canola and wheat.

2. Development of the Modified Plant

Rice is grown widely around the world as a staple food crop. These particular rice varieties are developed for use in the southern U.S. rice production region. The principal use of rice grain is as a food quality rice and the production of flour, which is used in a range of processed foods.

The mutation responsible for imidazolinone tolerance is due to a point mutation of a single nucleotide in the AHAS gene. BASF has identified the mutation in the AHAS gene which confers herbicide tolerance by sequencing the AHAS gene. The AHAS gene in PWC16 contains a single amino acid change that is due to a single nucleotide change in the coding sequence for AHAS. Previously approved imidazolinone tolerant rice, corn, canola, and wheat lines were the result of single nucleotide substitutions in the AHAS gene. The single amino acid change alters the binding site for the herbicide on the enzyme expressed by AHAS gene while having no effect on the normal functioning of the enzyme.

Single amino acid substitutions can affect the binding of AHAS inhibitors, such as imidazolinone herbicides, but there is no significant change in enzyme function, as reflected in enzymes studies of the mutant and wild-type enzymes from rice.

3. Product Information

A mutation in the AHAS enzyme in rice could affect the biosynthesis of the essential amino acids isoleucine, leucine, and valine. The amino acid composition of CL rice was compared to commercial cultivars, confirming that the AHAS activity of the imidazolinone-tolerant rice was not affected by the mutation.

4. Dietary Exposure

It is not anticipated that the dietary exposure to rice-based products will increase as a result of the sale of imidazolinone-tolerant rice. Many varieties of rice are available for cultivation and are assessed for quality and agronomic parameters before commercialization. The diversity of rice available ensures that a wide range of phenotypic traits are available; this, coupled with the normal variation in grain composition resulting from differences in the environmental growing conditions, results in a wide variation in the composition of commercial rice grain. Rice is mixed during storage, transportation and processing which produces consistency in composition of the commodity grain supply.

Imidazolinone tolerant Clearfield rice line PWC16 is expected to be used in similar applications as other rice varieties by the food industry.

5. Nutrition

The data submitted included analytical results for crude fat, crude fibre, protein, moisture, phytic acid and trypsin inhibitor, specific amino acids, fatty acids, minerals and vitamins. These were analyzed using standard AOAC or AOCS methods. There were no differences found between PWC16 and the wild type parent variety, Cypress, in the levels of any of these nutrients. The results for nutrient composition of the PWC16 rice grain were also comparable with those for the commercial varieties, Bengal, Wells, Drew, Cocodrie, submitted with a previous Clearfield rice submission bearing a different mutation (93AS3510), issued a letter of no objection by Health Canada on February 11, 2002.

6. Toxicology

No toxicity concerns are associated with the expression of the imidazolinone tolerance trait in rice. The AHAS protein is not homologous to known allergens or toxins and does not exhibit any characteristics of known food allergens. PWC16 rice does not express any new proteins or altered amounts of other proteins, including endogenous rice allergens. No allergenicity concerns are associated with the expression of this trait in rice.


Health Canada's review of the information presented in support of the food use of rice line PWC16, concluded that this line does not present human food safety concerns. Health Canada is of the opinion that rice line PWC16 and its derivatives are as safe and nutritious as currently available commercial rice varieties. Health Canada's opinion pertains only to the food use of rice line PWC16.

Health Canada's opinion deals only with the food use of imidazolinone tolerant rice. Issues related to its use as animal feed are 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.

For further information, please contact:

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

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