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. (c) 2012 Society of Chemical Industry