Expression of Accase Inhibitor Resistance in Seashore Paspalum with the Ile-1781 Mutation.

A non-GM herbicide resistant system was recently developed in the diploid species seashore paspalum using tissue culture and selection for mutants containing the ACCase Ile 1781 mutation. This mutation is known to confer high levels of resistance to many ACCase herbicides. Initial mutant lines were all heterozygotes and dose response experiments indicated even heterozygous lines expressed high levels of resistance to sethoxydim and fenoxaprop but lower levels of resistance to clethodim. In this study, newly developed lines that are homozygous for the Ile 1781 mutation were compared to heterozygous and wild type lines in greenhouse dose-response experiments using sethoxydim, fenoxaprop, and clethodim.  Herbicide dosages varied from 0 to 3200 grams a.i. ha^-1 and plant injury was measured at 21 days post treatment. Comparisons of herbicide injury of the heterozygous and homozygous lines showed that both were very resistant to sethoxydim and fenoxaprop with no differences in resistance expression between the heterozygous and homozogous lines. For clethodim, resistance expression was lower than to sethoxydim or fenoxaprop. The homozygous line did show improved but not total resistance to clethodim when compared to the heterozygous line.