Confirmation of ALS-Inhibiting Herbicide Resistant Annual Bluegrass: Herbicide Response and Genetic Analysis.

Annual bluegrass is commonly controlled by acetolactate synthase (ALS) inhibiting herbicides in managed turfgrass.  An annual bluegrass population with suspected resistance to ALS-inhibiting herbicides was collected from Grand National Golf Course in Opelika, Alabama (GN population).  Subsequent testing confirmed resistance of the GN population to foramsulfuron, trifloxysulfuron, bispyribac-sodium (bispyribac) and imazaquin when compared to a susceptible population collected locally at Auburn University (AU population). Sequencing of the ALS gene revealed a point mutation resulting in an amino acid substitution at Trp₅₇₄.  Cloning of the ALS gene surrounding the Trp₅₇₄ region yielded two distinct ALS gene sequences – one producing Trp₅₇₄ and one producing Leu₅₇₄.  Trp₅₇₄ to Leu has been previously correlated with resistance to ALS-inhibiting herbicides.  Both AU and GN gene sequences contained other similar silent and missense mutations.  This research confirms resistance of annual bluegrass to ALS-inhibiting herbicides with Trp₅₇₄ to Leu amino acid substitution being the most likely mode of resistance based on past literature.  A full report of this reseach has been accepted for publication in the journal Weed Science.