title: Glyphosate, paraquat and ACCase multiple herbicide resistance evolved in a Lolium rigidum biotype.
abstract: Glyphosate is the world's most widely used herbicide. A potential substitute for glyphosate in some use patterns is the herbicide paraquat. Following many years of successful use, neither glyphosate nor paraquat could control a biotype of the widespread annual ryegrass (Lolium rigidum), and here the world's first case of multiple resistance to glyphosate and paraquat is confirmed. Dose-response experiments established that the glyphosate rate causing 50% mortality (LD(50)) for the resistant (R) biotype is 14 times greater than for the susceptible (S) biotype. Similarly, the paraquat LD(50 )for the R biotype is 32 times greater than for the S biotype. Thus, based on the LD(50 )R/S ratio, this R biotype of L. rigidum is 14-fold resistant to glyphosate and 32-fold resistant to paraquat. This R biotype also has evolved resistance to the acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides. The mechanism of paraquat resistance in this biotype was determined as restricted paraquat translocation. Resistance to ACCase-inhibiting herbicides was determined as due to an insensitive ACCase. Two mechanisms endowing glyphosate resistance were established: firstly, a point mutation in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene, resulting in an amino acid substitution of proline to alanine at position 106; secondly, reduced glyphosate translocation was found in this R biotype, indicating a co-occurrence of two distinct glyphosate resistance mechanisms within the R population. In total, this R biotype displays at least four co-existing resistance mechanisms, endowing multiple resistance to glyphosate, paraquat and ACCase herbicides. This alarming case in the history of herbicide resistance evolution represents a serious challenge for the sustainable use of the precious agrochemical resources such as glyphosate and paraquat.
authors.affiliation: Western Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, Crawley, Perth, WA, Australia.
authors.forename: Qin
authors.initials: Q
authors.lastname: Yu
authors.forename: Andrew
authors.initials: A
authors.lastname: Cairns
authors.forename: Stephen
authors.initials: S
authors.lastname: Powles
mesh_terms: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000103:Acetyl-CoA Carboxylase / Q000037:antagonists & inhibitors*; D000595:Amino Acid Sequence; D005075:Biological Evolution; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology; D008129:Lolium / Q000187:drug effects* / Q000235:genetics*; D008969:Molecular Sequence Data; D010269:Paraquat / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000097797:Glyphosate
chemical_list: D051229:3-Phosphoshikimate 1-Carboxyvinyltransferase; D000103:Acetyl-CoA Carboxylase; D005998:Glycine; D006540:Herbicides; D010269:Paraquat; D010940:Plant Proteins; D000097797:Glyphosate