1. Sethoxydim Tolerance<br>Sethoxydim is a cyclohexanone herbicide registered in Canada for the control of annual and perennial grasses. Unmodified corn is not tolerant to sethoxydim, while broadleaved plants and some grasses such as annual ryegrass, green foxtail and red fescue are naturally tolerant to it. It is active against the enzyme acetyl-CoA-carboxylase (ACCase) of susceptible plants. <br>The enzyme ACCase catalyzes an important step in the biosynthesis of fatty acids necessary for membrane synthesis and maintenance, and for incorporation into triacylglycerides. Herbicide induced inhibition results in a lethal disruption of lipid biosynthesis. <br>Dekalb Canada Inc. selected a corn line, S2, that produces an altered ACCase enzyme that is not inhibited by the herbicide while retaining its normal catalytic properties. The mutation also resulted in some level of cross-tolerance to the related herbicides haloxyfop (not registered in Canada), fluazifop (Venture) and quizalofop (Assure). These herbicides all have the same mode of action through ACCase inhibition. <br>ACCase activities of unmodified corn and homozygous seedlings derived from S2 were shown to be similar in the absence of herbicide. A hundred fold higher sethoxidym concentration was required to inhibit half of the Poast compatible corn's ACCase activity, compared to the concentrations required to inhibit half of the unmodified corn's ACCase activity.<br>2. Development Method<br>Somatic embryos surviving on sethoxydim enriched media were selected, and the somaclonal variant cell line S2 was then selected. <br>The original S2 line was backcrossed with both parental lines of the hybrid at least six times.<br>3. Stable Integration into the Plant's Genome<br>Herbicide tolerance was consistently displayed by D404SR plants that were at least six generations away from the original variant. <br>The regenerated S2 plants were heterozygous for the mutant allele. The sethoxydim tolerance trait was shown to be inherited as a single partially dominant allele.<br>4. Nutrition<br>Nutritional composition for the modified and unmodified corn lines was compared. The selection of DK412SR and DK404SR corn lines through somaclonal variation has had no meaningful effect on the corn plant nutrient levels. The use of corn products derived from DK412SR and DK404SR corn lines would therefore have no significant impact on the nutritional quality of the Canadian food supply.