ARCHIVED - Imidazolinone Tolerant Rice

February, 2002

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 lines CL 121, CL141,CFX51 and their derivatives (CLEARFIELD, or CL rice) derived 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 was tolerant to imidazolinone herbicides with a mutation designated 93AS3510. The basis for the herbicide tolerance is 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 imidazolinone tolerant rice was developed through conventional mutation breeding of AS3510 rice, followed by crossing with commercial rice varieties Cocodrie, Maybelle and Cypress. Since recombinant techniques were not used, no foreign DNA was introduced to achieve the herbicide tolerant trait. The method used for obtaining imidazolinone-tolerant rice was chemical mutagenesis with ethyl methane sulfonate. One imidazolinone-tolerant seedling was obtained (93AS3510). The 93AS3510 mutation affects the acetohydroxyacid synthase (AHAS) enzyme of rice at a specific location. The AHAS enzyme catalyses the first step in the biosynthesis of the branched chain amino acids isoleucine, leucine and valine in plants. The mutation in the AHAS enzyme results in an alteration to the binding site for the imidazolinone class of herbicide, therefore increasing the plant's tolerance to those herbicides. The other properties of the AHAS enzyme are unaffected.

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.

5. Nutrition

The data presented on the amino acid composition of imidazolinone-tolerant rice demonstrates that the AHAS mutation does not alter the levels of the amino acids valine, leucine or isoleucine. Proximate analysis confirms that CL rice has the nutritional composition typical of conventional rice.

6. Toxicology

No toxicity concerns are associated with the expression of the imidazolinone tolerance trait in rice. No new protein, or significantly altered protein, is produced through this mutation. No allergenicity concerns are associated with the expression of this trait in rice.


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. It can be concluded that the single amino acid substitution in the 93AS3510 mutation will result in rice that is unchanged in its nutritional and food safety characteristics when compared to other rice varieties currently used as food in Canada.

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.

(Également disponible en français)

For further information, please contact:

Office of Food Biotechnology
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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