ANNUAL BLUEGRASS (Poa annua) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: TRYPTOPHAN 574 to LEUCINE
Annual Bluegrass (Poa annua) is a monocot plant in the poaceae family. A single amino acid substitution from Tryptophan 574 to Leucine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Annual Bluegrass

Chemical Family	Example Herbicide	Resistance Level
Imidazolinones	Imazethapyr	Resistant > 10 fold
Pyrimidinyl benzoates	Bispyribac-Na	Resistant > 10 fold
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidine - Type 1	Chloransulam-methyl	Not Determined
Triazolinones	Flucarbazone-Na	Not Determined

REFERENCES

McElroy, J. S. ; Flessner, M. L. ; Wang, Z. Y. ; Dane, F. ; Walker, R. H. ; Wehtje, G. R.. 2013. A Trp₅₇₄ to leu amino acid substitution in the ALS gene of annual bluegrass (Poa annua) is associated with resistance to ALS-inhibiting herbicides. Weed Science 61 : 21 - 25.

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, AL (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..

This case was entered by Patrick Tranel Email: tranel@illinois.edu

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