title: Evolution of herbicide resistance in weeds: initial frequency of target site-based resistance to acetolactate synthase-inhibiting herbicides in Lolium rigidum.
abstract: The frequency of individuals resistant to two acetolactate synthase (ALS)-inhibiting herbicides in three previously untreated populations of Lolium rigidum was determined. The frequency of individuals resistant to the sulfonylurea herbicide sulfometuron-methyl varied from 2.2 x 10(-5) to 1.2 x 10(-4) and the frequency of individuals resistant to the imidazolinone herbicide imazapyr varied from 1 x 10(-5) to 5.8 x 10(-5) depending on the population. Application of sulfometuron-methyl selected individuals with a herbicide-insensitive ALS, which was also cross-resistant to imazapyr. The high initial frequency of individuals resistant to ALS-inhibiting herbicides in L. rigidumpopulations never previously exposed to these herbicides helps explain the rapid evolution of herbicide resistance in this species once ALS-inhibiting herbicides were used.
authors.affiliation: CRC for Weed Management Systems and Department of Applied and Molecular Ecology, Waite Campus, University of Adelaide, SA, Australia. christopher.preston@adelaide.edu.au
authors.forename: C
authors.initials: C
authors.lastname: Preston
authors.forename: S B
authors.initials: SB
authors.lastname: Powles
mesh_terms: D000095:Acetolactate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D005075:Biological Evolution; D004351:Drug Resistance / Q000235:genetics; D006540:Herbicides / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology*; D008129:Lolium / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D009525:Niacin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013453:Sulfonylurea Compounds / Q000494:pharmacology*
chemical_list: D006540:Herbicides; D007093:Imidazoles; D013453:Sulfonylurea Compounds; D009525:Niacin; C076656:imazapyr; D000095:Acetolactate Synthase; C042031:sulfometuron methyl