The Presence of Two Different Target-site Resistance Mechanisms in Individual Plants of Alopecurus Myosuroides Huds., Identified Using a Quick Molecular Test for the Characterisation of Six ALS and Seven ACCase SNPs

Background: Target-site resistance to ALS- and ACCase-inhibiting herbicides in the grass weed Alopecurus myosuroides is associated with well-characterised allelic variants encoding ALS- and ACCase-based resistance. The potential for combined ALS and ACCase resistance presents a threat to future control, given the extent to which these herbicides are used. The authors present a primer extension method for rapid detection of known resistance-conferring substitutions.

Results: Individuals showing combined resistance to field-rate mesosulfuron + iodosulfuron and cycloxydim were identified in four field-collected populations, with proportions ranging from 30 to 100%. Genotyping with the SNaPshot primer extension kit showed the T197 and L574 ALS and L1781 ACCase isoforms to be associated with ALS and ACCase resistance whenever they occurred.

Conclusion: Combined ALS and ACCase target-site resistance threatens future control of A. myosuroides. The SNaPshot extension assay provides a reliable new multiplexable method for characterising known allelic variants of the ALS and ACCase genes of A. myosuroides. The method offers significant advantages over both CAPS/dCAPS and PASA in that full genotyping can be accomplished at any nucleotide position using a single extension primer.