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1 October 2015 Molecular Basis of Evolved Resistance to Glyphosate and Acetolactate Synthase-Inhibitor Herbicides in Kochia (Kochia scoparia) Accessions from Montana
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Abstract

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 dose–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 μM 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 (~ 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.

Nomenclature: Glyphosate; metsulfuron methyl; thifensulfuron methyl; tribenuron methyl; Kochia, Kochia scoparia (L.) Schrad.

© 2015 Weed Science Society of America
Vipan Kumar, Prashant Jha, Darci Giacomini, Eric P. Westra, and Philip Westra "Molecular Basis of Evolved Resistance to Glyphosate and Acetolactate Synthase-Inhibitor Herbicides in Kochia (Kochia scoparia) Accessions from Montana," Weed Science 63(4), 758-769, (1 October 2015). https://doi.org/10.1614/WS-D-15-00021.1
Received: 4 February 2015; Accepted: 1 April 2015; Published: 1 October 2015
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