Molecular Basis of Evolved Resistance to Glyphosate & Acetolactate Synthase-Inhibitor Herbicides in Kochia (Kochia scoparia) Accessions from Montana
Westra, Eric P.
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The rapid evolution and spread of glyphosate-resistant (GR) kochia in the Northern Great Plains is an increasing threat to GR cropping systems and conservation tillage practices common in this region. GR kochia accessions with 4.6- to 11-fold levels of resistance to glyphosate have recently been reported in Montana. Those GR kochia accessions were also suspected to be resistant to acetolactate synthase (ALS) inhibitors, i.e., multiple herbicide-resistant (MHR) kochia. In this research, the level of resistance to the ALS-inhibitor herbicides (sulfonylureas) and the molecular mechanisms conferring resistance to glyphosate and ALS-inhibitor herbicides in MHR kochia was investigated. On the basis of whole-plant doseâ€“response assays, MHR kochia accessions (GIL01, JOP01, and CHES01) were 9.3- to 30-fold more resistant to premixed thifensulfuron methyl + tribenuron methyl + metsulfuron methyl than the susceptible (SUS) accession. In an in vivo leaf-disk shikimate assay, MHR plants accumulated less shikimate than the SUS plants at a discriminate dose of 100 Î¼M glyphosate. Sequencing of the conserved region of EPSPS revealed no target-site mutation at Thr102 or Pro106 residue. MHR kochia accessions had increased relative EPSPS gene copies (~â€‰4 to 10) compared with the SUS accession (single copy). Furthermore, MHR kochia accumulated higher EPSPS protein compared with the SUS plants. Resistance to the ALS-inhibitor herbicides was conferred by Pro197 amino acid substitution (proline to glutamine). EPSPS gene amplification and a single target-site mutation at Pro197 in ALS gene confer resistance to glyphosate and ALS-inhibitor herbicides, respectively, in MHR kochia accessions from Montana. This is the first confirmation of occurrence of MHR kochia in Montana.
Kumar, Vipan, Prashant Jha, Darci Giacomini, Eric P. Westra, and Philip Westra. "Molecular Basis of Evolved Resistance to Glyphosate & Acetolactate Synthase-Inhibitor Herbicides in Kochia (Kochia scoparia) Accessions from Montana." Weed Science 63, no. 4 (October-December 2015): 758-769. DOI:https://dx.doi.org/10.1614/WS-D-15-00021.1.