title: Investigating the mechanisms of glyphosate resistance in Lolium multiflorum.
abstract: Evolved resistance to the herbicide glyphosate has been reported in eleven weed species, including Lolium multiflorum. Two glyphosate-resistant L. multiflorum populations were collected, one from Chile (SF) and one from Oregon, USA (OR), and the mechanisms conferring glyphosate resistance were studied. Based on a Petri dish dose-response bioassay, the OR and the SF populations were two and fivefold more resistant to glyphosate when compared to the susceptible (S) population, respectively; however, based on a whole-plant dose-response bioassay, both OR and SF populations were fivefold more resistant to glyphosate than the S population, implying that different resistance mechanisms might be involved. The S population accumulated two and three times more shikimic acid in leaf tissue 96 h after glyphosate application than the resistant OR and SF populations, respectively. There were no differences between the S and the glyphosate-resistant OR and SF populations in 14C-glyphosate leaf uptake; however, the patterns of 14C-glyphosate translocation were significantly different. In the OR population, a greater percentage of 14C-glyphosate absorbed by the plant moved distal to the treated section and accumulated in the tip of the treated leaf. In contrast, in the S and in the SF populations, a greater percentage of 14C-glyphosate moved to non-treated leaves and the stem. cDNA sequence analysis of the EPSP synthase gene indicated that the glyphosate-resistant SF population has a proline 106 to serine amino acid substitution. Here, we report that glyphosate resistance in L. multiflorum is conferred by two different mechanisms, limited translocation (nontarget site-based) and mutation of the EPSP synthase gene (target site-based).
authors.affiliation: Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331-3002, USA. perezjoa@oregonstate.edu
authors.forename: Alejandro
authors.initials: A
authors.lastname: Perez-Jones
authors.forename: Kee-Woong
authors.initials: KW
authors.lastname: Park
authors.forename: Nick
authors.initials: N
authors.lastname: Polge
authors.forename: Jed
authors.initials: J
authors.lastname: Colquhoun
authors.forename: Carol A
authors.initials: CA
authors.lastname: Mallory-Smith
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000737:chemistry / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001483:Base Sequence; D001692:Biological Transport; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance / Q000235:genetics / Q000502:physiology; D006540:Herbicides / Q000494:pharmacology*; D008129:Lolium / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012765:Shikimic Acid / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D005998:Glycine; D006540:Herbicides; D012765:Shikimic Acid; D000097797:Glyphosate