Database Product Description
- Host Organism
- Brassica napus (Argentine Canola)
- Trade Name
- Westar Roundup Ready®
- Glyphosate herbicide tolerance.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Monsanto Company
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Brassica napus (Argentine Canola) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Argentine or oilseed rape (Brassica napus) was grown as a commercial crop in over 50 countries, with a combined harvest of 48.9 million metric tonnes in 2006. The major producers of rapeseed are China, Canada, India, Germany, France, the United Kingdom and Australia. Canola is a genetic variation of B. napus that was developed through conventional breeding to contain low levels of the natural rapeseed toxins, glucosinolate and erucic acid. Canola is grown for its seed, which represents a major source of edible vegetable oil and is also used in livestock feeds.
The only food use of canola is as a refined oil. Typically, canola oil is used by itself as a salad oil or cooking oil, or blended with other vegetable oils in the manufacture of margarine, shortenings, cooking and salad oils. Canola meal, a byproduct of the oil production process, is added to livestock feed rations. An increasing amount of oil is being used for biodiesel production, especially in Europe.
The removal of weeds early in the growing season is extremely important in canola production. Young canola seedlings are not very competitive and early weed pressure has detrimental effects on final yield. Precautions such as preplant tillage or herbicide application are common approaches for reducing weed competition. Once established, canola forms a dense canopy and is very competitive, making weed control less of a concern.
At present, it is expensive, but possible, to control annual grassy weeds (wild oats, volunteer cereals), perennial weeds (Canada thistle, perennial sow thistle, quackgrass), and certain annual broadleaf weeds in canola. The broadleaves are the most difficult to control because there are few herbicide options available. Many producers will use as many as four herbicides per year in an effort to control weeds.
Traditionally, it has been difficult to manage weeds in canola rotations because of the need to use Group 1 herbicides (Assure®, Fusion®, Poast®, Select®, Venture DG®) that are also commonly used to control weeds in flax, wheat and other cereals. Growers favour these herbicides because they are easy to work with, are extremely effective, and may be applied over a period of time. However, the constant use of Group 1 herbicides has placed large acreages of cultivated land at high risk of developing Group 1 weed resistance. The establishment of several herbicide-tolerant weed populations demonstrates this problem.
The herbicide-tolerant canola line GT73 (synonym RT73) was developed to allow for the use of glyphosate, the active ingredient in the herbicide Roundup®, as a weed control option. In order to obtain field tolerance to glyphosate herbicide, two genes, CP4 EPSPS and goxv247, were introduced into B. napus cv. Westar by Agrobacterium-mediated transformation
The EPSPS gene codes for the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) that is present in all plants, bacteria and fungi. The EPSPS gene put into GT73 was isolated from strain CP4 of the common soil bacterium Agrobacterium tumefaciens and is a glyphosate tolerant form of EPSPS. The EPSPS enzyme is part of an important biochemical pathway in plants called the shikimate pathway, which is involved in the production of aromatic amino acids and other aromatic compounds. When conventional canola plants are treated with glyphosate, the plants cannot produce the aromatic amino acids needed to grow and survive. EPSPS is not present in mammals, birds or aquatic life forms, which do not synthesize their own aromatic amino acids. For this reason, glyphosate has little toxicity to these organisms. The EPSPS enzyme is naturally present in foods derived from plant and microbial sources.
The canola line GT73 contains a second gene that codes for a modified version of glyphosate oxidase (GOX) enzyme that is ubiquitous in nature. The goxv247 gene inserted into GT73 was isolated from strain LBAA of the bacterium Ochrobactrum anthropi. Glyphosate oxidase (GOX) enzyme accelerates the normal breakdown of the herbicide glyphosate into two non-toxic compounds, aminomethylphosphonic acid (AMPA) and glyoxylate. AMPA is the principal breakdown product of glyphosate and is degraded by several microorganisms, while glyoxylate is commonly found in plant cells and is broken down by the glyoxylic pathway for lipid metabolism.
GT73 has been tested in field trials in Canada since 1992 and the United States since 1995. Agronomic and adaptation characteristics such as germination, vegetative vigour, overwintering capacity, seed production (yield), agronomic characteristics (such as time to flowering, maturity) and disease and insect resistance were all found to be within the normal range when compared to conventional canola. GT73 did not pose a plant pest risk, negatively affect beneficial or nontarget organisms, exhibit enhanced weediness potential, and was not expected to impact on threatened or endangered species.
B. napus may outcross (up to 30% of the time) with plants of the same species, and potentially with plants of related species B. rapa, B. juncea, B. carinata, B. nigra, Diplotaxis muralis, Raphanus raphanistrum, and Erucastrum gallicum. Previous studies have demonstrated that cross breeding is most likely to occur with B. rapa. Because of the ability of canola to outcross with related plants, the formation of glyphosate tolerant hybrids is possible. However, the glyphosate-tolerance trait is not expected to provide a competitive advantage to hybrid plants unless grown in managed environments routinely subjected to glyphosate applications. In the event that a glyphosate tolerant hybrid survived, the herbicide-tolerant individual could be easily controlled using mechanical and/or other available chemical means.
The human consumption of canola products is limited to the purified oil. Refined edible canola oil consists of purified triglycerides (96-97%) and does not contain any detectable protein, hence no amounts of CP4 EPSPS or GOX proteins were detected in the refined oil of GT73 canola. The fatty acid composition of GT73 was within the normal range for canola oil. GT73 contained less than 2% erucic acid and less than 30 micromoles/g glucosinolates in the oil-free meal, meeting published standards for canola oil.
The livestock feed safety of GT73 was established based on several standard criteria. The analysis of nutrients from GT73 and non-transgenic canola did not reveal any significant differences in the levels of crude protein, crude fat, crude fibre, ash and gross energy in either whole seed or processed meal. Levels of the shikimate pathway aromatic amino acids phenylalanine, tyrosine and tryptophan extracted from both transgenic GT73 and non-transgenic canola were statistically the same. These results demonstrated that the introduction of the novel genes in GT73 do not result in any secondary effects impacting on composition or nutritional quality.
Animal feeding studies included a four-week rat study on processed and unprocessed meal, a ten-week trout study on processed meal, and a five-day quail study on unprocessed meal. The studies all supported the wholesomeness of meal from glyphosate-tolerant canola as a component in animal feed.
It was determined that there were no toxicity and allergenicity concerns with GT73. There is no dietary exposure to CP4 EPSPS and GOX since these proteins are not present in the refined canola oil consumed by humans. Furthermore, the structure and function of CP4 EPSPS protein was determined to be similar to the same enzyme naturally present in foods and livestock feeds. Neither CP4 EPSPS nor GOX were found to have any amino acid sequence similarities with known toxins or allergens, and there are no known reports of toxicity or allergenicity of CP4 EPSPS or GOX proteins from plants, bacteria and fungi. Direct laboratory studies of the CP4 EPSPS and GOX proteins provided further evidence supporting the lack of toxicity or allergenicity concerns with GT73.
Links to Further Information Expand
This record was last modified on Monday, August 22, 2016