<p style="text-align: justify;">Clearfield&trade; sunflower hybrid X81359 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. X8159 is not intended for cultivation in Canada.</p>

<p style="text-align: justify;">Sunflower (<i>Helianthus annuus</i> L.) was grown as a commercial crop in 67 countries, with a combined harvest 31 million metric tonnes in 2006. The major producers of sunflower in 2004 were Russia, Ukraine, Argentina, China, Romania and France. Sunflower is cultivated as an oilseed crop, as well as for the production of edible seeds for human consumption. Sunflower oil is used in cooking and in the production of margarine, salad dressings and baby formula. Industrial uses of sunflower oil include soaps, hydraulic fluids, paints and plastics. The byproduct of oil extraction, sunflower meal, is used as a livestock feed (CFIA, 2005a).</p>

<p style="text-align: justify;">Weeds are a major production problem in sunflower cultivation. Sunflower is a poor competitor during the early growth stages until canopy closure and weeds during these growth stages compete for light, water and nutrients. Weeds can be managed using a combination of cultural practices (<i>e.g.</i>, inter-row cultivation), integrated weed management (<i>e.g.</i>, weed scouting, economic thresholds) and the use of herbicides. Herbicides can be applied before the crop emerges (<i>e.g.</i>, ethalfluraline, trifluralin), or after (<i>e.g.</i>, imazamethabenz, clethodim, fluazifop-p-butyl). 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.</p>

<p style="text-align: justify;">Clearfield&trade; sunflower hybrid X81359 was developed to allow the use of imidazolinone herbicides as a post-emergence weed control option in sunflower 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 alpha-ketoglutarate, all of which causes the eventual death of the plant. While unmodified sunflower is not tolerant to imidazolinone, X81359 has been modified to survive an otherwise lethal application of this herbicide. The tolerance to imidazolinone herbicides in X81359 is due to a naturally occurring mutation in the AHAS gene in a wild population of <i>Helianthus annus</i>. This trait was introduced into X81359 using conventional plant breeding techniques.</p>

<p style="text-align: justify;">The livestock safety of X81350 was based on the 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 X81350 compared to conventional sunflower was demonstrated by the analysis of key nutrients in the grain including proximates (<i>e.g.</i>, crude protein, crude fat, crude fibre, ash, moisture), amino acids (valine, leucine and isoleucine), and fatty acids, as well as by the composition in anti-nutritional factors (phytic acid and trypsin inhibitor).</p>
