title: Resistance mechanism to bensulfuron-methyl in biotypes of Scirpus mucronatus L. collected in Chilean rice fields.
abstract: Two biotypes of Scirpus mucronatus not controlled with the herbicide bensulfuron-methyl in rice fields were characterized by using field, greenhouse, and laboratory techniques. Seeds were collected in two rice areas [Parral (R1) and Linares (R2)], where bensulfuron-methyl at 150 g ha(-1) did not control S. mucronatus. A third seed sample of S. mucronatus susceptible (S) to bensulfuron-methyl was collected in an area from Chile. The dose-response studies confirmed resistance to bensulfuron-methyl in R1 and R2 S. mucronatus biotypes; ratios (R/S) of the ED(50) values of resistant to susceptible plants were 1719 and 1627 for R1 and R2, respectively. The biotype R1 also showed strong cross-resistance (ratios ranging from 1719 to 43) to sulfonylureas (bensulfuron-methyl, cyclosulfamuron, ethoxysulfuron, imazosulfuron, and pyrazosulfuron-ethyl) and imidazolinone (imazamox) and a weak cross-resistance (ratio of 1.705) to pyrimidinyloxybenzoates (bispyribac-sodium), all ALS inhibiting herbicides used in rice. Absorption, translocation, and metabolism results did not explain the differences in susceptibility among biotypes. The in vitro assays confirmed cross-resistance to all ALS inhibitors tested and the level of cross resistance was bensulfuron-methyl > imazosulfuron ≫ cyclosulfamuron ≫ pyrazosulfuron-ethyl ≫ ethoxysulfuron > imazamox ≫ bispiribac-sodium. Molecular studies demonstrated that the Pro197His amino acid substitution on the ALS enzyme could explain the loss of affinity for the ALS-inhibiting herbicides.
authors.affiliation: Department of Agricultural Chemistry and Edaphology, University of Cordoba, 14071 Cordoba, Spain.
authors.forename: Hugo
authors.initials: H
authors.lastname: Cruz-Hipolito
authors.forename: Maria D
authors.initials: MD
authors.lastname: Osuna
authors.forename: Ribas A
authors.initials: RA
authors.lastname: Vidal
authors.forename: Rafael
authors.initials: R
authors.lastname: De Prado
mesh_terms: D000095:Acetolactate Synthase / Q000037:antagonists & inhibitors / Q000737:chemistry; D000595:Amino Acid Sequence; D002677:Chile; D029785:Cyperaceae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053209:Herbicide Resistance; D012275:Oryza / Q000254:growth & development*; D012639:Seeds / Q000187:drug effects; D013453:Sulfonylurea Compounds / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D013453:Sulfonylurea Compounds; C071475:methyl bensulfuron; D000095:Acetolactate Synthase