title: EPSPS Gene Amplification in Glyphosate-Resistant Italian Ryegrass (Lolium perenne ssp. multiflorum) Populations from Arkansas (United States).
abstract: Glyphosate-resistant Italian ryegrass was detected in Arkansas (United States) in 2007. In 2014, 45 populations were confirmed resistant in eight counties across the state. The level of resistance and resistance mechanisms in six populations were studied to assess the severity of the problem and identify alternative management approaches. Dose-response bioassays, glyphosate absorption and translocation experiments, herbicide target (EPSPS) gene sequence analysis, and gene amplification assays were conducted. The dose causing 50% growth reduction (GR50) was 7-19 times higher for the resistant population than for the susceptible standard. Uptake and translocation of (14)C-glyphosate were similar in resistant and susceptible plants, and no mutation in the EPSPS gene known to be associated with resistance to glyphosate was detected. Resistant plants contained from 11- to >100-fold more copies of the EPSPS gene than the susceptible plants, whereas the susceptible plants had only one copy of EPSPS. Plants surviving the recommended dose of glyphosate contained at least 10 copies. The EPSPS copy number was positively related to glyphosate resistance level (r = 80). Therefore, resistance to glyphosate in these populations is due to multiplication of the target site. Resistance mechanisms could be location-specific. Suppressing the mechanism for gene amplification may overcome resistance.
authors.affiliation: †Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas 72704, United States.
authors.forename: Reiofeli A
authors.initials: RA
authors.lastname: Salas
authors.affiliation: §University of Arkansas Extension, P.O. Box 357, Lonoke, Arkansas 72086, United States.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Scott
authors.affiliation: #Natural Products Utilization Research Unit, Thad Cochran Research Center, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 1848, University, Mississippi 38677, United States.
authors.forename: Franck E
authors.initials: FE
authors.lastname: Dayan
authors.affiliation: †Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas 72704, United States.
authors.forename: Nilda R
authors.initials: NR
authors.lastname: Burgos
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000235:genetics*; D001131:Arkansas; D005784:Gene Amplification; D018628:Gene Dosage; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D008129:Lolium / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D005998:Glycine; D006540:Herbicides; D010940:Plant Proteins; D000097797:Glyphosate
keywords: 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS); Italian ryegrass (Lolium perenne ssp. multiflorum); gene amplification; glyphosate resistance