Development and characterization of wheat mutants resistant to acetyl co-enzyme A carboxylase inhibitors

Weed management in bread wheat (Triticum aestivum L.) is currently limited when undesirable grass species are present due to limited options for herbicidal selectivity between the species. The incorporation of an acetyl co-enzyme A carboxylase (ACCase) inhibitor tolerance trait in wheat would allow growers to expand the arsenal and effectiveness available for managing troublesome grass species. To develop this new trait, ethyl methanesulfonate mutagenesis (EMS) was utilized to induce point mutations in the ACCase gene. Seeds mutagenized with 0.75% EMS for 2.5 hours were grown and seed was collected. Lethal applications of clethodim and quizalofop were applied to plants in the M2 generation. Approximately 200 surviving plants were collected out of the total of 2.5 million M2 seeds planted. M3 greenhouse screening revealed roughly half the plants selected with quizalofop in the M2 generation contained an increased level of resistance to the herbicide. Dose response studies confirmed a two- to- eight fold increase in resistance over wild-type wheat and limited cross-resistance across other ACCase inhibiting herbicides. DNA sequencing of the ACCase gene in quizalofop mutants uncovered a novel point mutation resulting in a Ala -> Val substitution at position 2004 from the Alopecurus myosuroides numbering scheme. A 14 C-based enzyme assay established a three- to- ten fold increase in ACCase activity in the presence of quizalofop from plants containing the new mutation. The experiment successfully generated quizalofop resistant mutant wheat and led to the discovery of a previously unknown point mutation. This mutation has the potential for future implementation in a wheat cultivar resistant to quizalofop.