Database Product Description
- Host Organism
- Triticum aestivum (Wheat)
- Imidazolinone herbicide tolerance.
- Trait Introduction
- Chemically induced seed mutagenesis
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- BASF Inc.
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Triticum aestivum (Wheat) Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
BW255-2 and BW238-3 (Clearfield™) bread wheat was not subject to regulation in any jurisdiction except Canada since the development of this herbicide-tolerant line did not employ recombinant DNA technologies. In Canada, regulatory approval is required for use in human food and livestock feed, and for environmental release.
Commercial wheat is comprised mainly of two species: common, or bread wheat (T. aestivum L.) and durum wheat (T. durum Desf.). Bread wheat is classified into several types, based on the spring and winter forms of growth habit, and the hardness of the kernels. Winter wheat requires vernalisation to produce flowers, whereas spring wheat does not have this requirement. The hard types of bread wheat are high in protein, especially gliadins and glutenins. The high levels of these protein fractions in the flour impart elasticity to bread dough and allow it to expand during leavening and baking. Soft wheats are low in protein, and have low levels of gliadin and glutenin; these qualities are desirable in products such as cakes and pastries, and in unleavened breads. Durum wheat produces very hard, almost vitreous kernels due to its high protein content. This wheat is milled into semolina for the production of pasta and couscous.
Harvested wheat consists of a naked kernel, unlike other cereals such as rice, barley or oats that retain their hull (i.e., the palea and lemma). The wheat kernel is loosely enclosed within the palea and lemma of each spikelet; these are eliminated as chaff during threshing. The wheat kernel is milled into white flour by removing the bran, aleurone layers and the germ prior to grinding; whole-wheat flour retains these fractions. By-products of wheat milling include: bran, germ, shorts and middlings. Some of these by-products are used as human food (i.e., bran, germ), and others, as livestock feed. Grain that does not meet the grade for food use can be used as animal feed, mainly for poultry and swine, but also for cattle. Wheat can also be fed as forage, either as pasture prior to stem elongation, or as ensilage. Wheat is also used in the brewing and distilling industries.
Weeds are a major production problem in wheat cultivation. Weeds compete for light, water and nutrients, and can also cause lodging and problems with harvesting. The seeds of several weed species are almost impossible to clean out of harvested wheat (e.g., Avena fatua L. wild oats), causing loss of quality and downgrading of the crop. Weeds can be managed using a combination of cultural practices (e.g., seed bed preparation, use of clean [certified] seed, narrow row spacing, fertilizer banding), integrated weed management (e.g., weed scouting, economic thresholds) and the use of herbicides. Depending on the weed species present, herbicides can be applied before the crop emerges (e.g., amitrole, glyphosate, trifluralin), or after (e.g., 2-4D, bromoxynil, dicamba, fenoxaprop-p-ethyl, MCPA, metsulfuron methyl). The build-up of weed populations can be stemmed by applying herbicides on summer-fallowed fields, and by practicing crop rotation, which allows the use of different herbicides. Rotating among herbicide groups also prevents the development of herbicide-resistant biotypes.
BW255-2 and BW238-3 (Clearfield™) bread wheat lines were developed to allow the use of imidazolinone herbicides, as a weed control option in spring wheat production. The mode of action of imidazolinone herbicides consists of inhibiting the activity of acetohydroxyacid synthase (AHAS), an enzyme in plants active in glycolysis and in the biosynthesis of the branched-chain amino acids isoleucine, leucine and valine. The result of the inhibition of AHAS activity is a decrease in protein synthesis and an accumulation of toxic levels of ?-ketoglutarate, which causes the eventual death of the plant. While unmodified wheat is not tolerant to imidazolinone herbicides, BW255-2 and BW238-3 have been modified to survive an otherwise lethal application. BW255-2 and BW238-3 were developed using chemically induced seed mutagenesis and whole plant selection procedures. The herbicide tolerance is due to a single point mutation in the AHAS gene, such that the resulting enzyme has a single amino acid substitution and is no longer affected by imidazolinone herbicides.
Events BW255-2 and BW238-3 have been field tested in multiple locations in Canada in 1999 and in the United States in 2003. Data collected from replicated field trials demonstrated that BW255-2 and BW238-3 did not differ significantly from the parental line in terms of vegetative vigour, time to maturity, seed production (yield), disease resistance, and tendency to weediness.
The potential for transfer of the herbicide tolerant trait from BW255-2 and BW238-3 wheat to other nonmodified wheat plants, or to wild relatives of wheat, has been investigated. Common wheat (T. aestivum) is primarily self-pollinating. While outcrossing can occur by wind-pollination, the rates are usually very low (< 10%). Under the most ideal conditions, outcrossing will occur to nearby plants, but does not usually occur 3 m beyond the source plant. Given the variability of outcrossing rates among genotypes, an isolation distance of 30 m is required for certified seed production.
The potential for introgression of the novel trait into weedy relatives of wheat in Canada and the United States is also very low. Two species closely related to wheat are Aegilops cylindria Host (jointed goat grass) and Agropyron repens (L.) Beauv. (quackgrass). Both are introduced species and are considered weedy and invasive. Recent research has shown a possibility of hybridization between wheat and jointed goatgrass. Introgression of an herbicide tolerant trait from wheat into jointed goatgrass would confer an additional advantage to this weedy species.
The food and livestock safety of BW255-2 and BW238-3 wheat was based on: the evaluation of the similarity of AHAS, in structure and function, to the enzyme naturally present in food and livestock feeds; the lack of toxicity or allergenicity of the modified AHAS. The nutritional equivalence and wholesomeness of BW255-2 and BW238-3 wheat compared to conventional wheat was demonstrated by the analysis of key nutrients in the grain including proximates (e.g., crude protein, crude fat, crude fibre, ash, moisture), branched chain amino acids (valine, leucine and isoleucine), essential amino acids (cystine, methionine, threonine and lysine) fatty acid composition, vitamins and minerals, as well the levels of anti-nutrients (phytic acid and trypsin inhibitor). Significant differences were observed between BW255-2 and BW238-3 and parental controls for some of the tested nutrients, but levels of all parameters measured were within the range of conventional bread wheat varieties.
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This record was last modified on Friday, March 26, 2010