Database Product Description
- Host Organism
- Triticum aestivum (Wheat)
- Imidazolinone herbicide tolerance, specifically imazethapyr.
- 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
Teal 11A (Clearfield™) spring 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 was 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 vernalisation requirement (winter and spring types) and kernel hardness. 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.
Teal 11A (Clearfield™) spring wheat was developed to allow the use of imazamox and imazethapyr, both imidazolinone herbicides, as weed control options in spring wheat production. The mode of action of imazamox and imazethapyr 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 in an accumulation of toxic levels of alpha-ketoglutarate, all of which causes the eventual death of the plant. While unmodified wheat is not tolerant to either imazamox or imazethapyr, the line Teal 11A has been modified to survive an otherwise lethal application of these herbicides. Teal 11A was developed using chemically induced seed mutagenesis and whole plant selection procedures. The herbicide tolerance is due to a mutation in the AHAS gene, which codes for an alteration in the binding site for imazamox in the AHAS enzyme.
Teal 11A spring wheat has been field tested in Canada in Saskatchewan and the United States, in Minnesota and North Dakota, from 1999 to 2001. Data collected from replicated field trials demonstrated that Teal 11A did not differ significantly from the parental line in terms of vegetative growth, time to maturity, seed production (yield), disease resistance, and tendency to weediness.
The potential for transfer of the herbicide tolerant trait from Teal 11A 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 low (Wild species closely related to T. aestivum in the continental United States and Canada are Aegilops cylindria Host (jointed goatgrass) and Agropyron repens (L.) Beauv. (quackgrass). Both of these are introduced species, native to Eurasia, and are considered weedy and invasive in Canada and the United States. Jointed goatgrass is an annual, found in most of the United States, but not in Canada. It is considered a noxious weed in British Columbia due to the proximity of populations in Washington, Idaho and Montana, but is also found in other states contiguous to Canada, i.e., North Dakota, Michigan, Ohio and New York. It would not be expected to become established in Canada except in southwestern British Columbia and southwestern Ontario (Darbyshire, 2003). Hybridization of jointed goatgrass with wheat can occur under field conditions and has been reported in wheat fields in Oregon. The hybridization was successful to the first backgross generation with jointed goat grass as the female plant. This has raised concerns of possible introgression of wheat into jointed goatgrass populations (Morrison et al., 2002). Quackgrass is a perennial species found extensively in Canada and the United States. Reports of hybridization between wheat and quackgrass have been reported; however, these have not been successfully reproduced by manual pollination (CFIA, 1999). Due to the doubtful nature of any hybridization between wheat and quackgrass, gene introgression into quackgrass populations is not expected to occur.
The food and livestock safety of Teal 11A wheat was based on an evaluation of the similarity of AHAS, in structure and function, to the enzyme naturally present in food and livestock feeds, and the lack of toxicity or allergenicity of the modified AHAS. The nutritional equivalence and wholesomeness of Teal 11A 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), amino acids, fatty acids, B vitamins (thiamine, niacin, panthothenic acid, and pyridoxine), and minerals (phosphorus, magnesium, zinc and iron), as well the composition in the anti-nutrients phytic acid and trypsin inhibitor.
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This record was last modified on Friday, March 26, 2010