title: Cross-resistance of horseweed (Conyza canadensis) populations with three different ALS mutations.
abstract: BACKGROUND
  Horseweed is a weed commonly found in agronomic crops, waste areas and roadsides. Resistance to ALS-inhibiting herbicides in horseweed was first reported in 1993 in a population from Israel. Resistance to ALS-inhibiting herbicides in horseweed is now widespread, but, as of now, the resistance mechanism has not been reported.
  
  
  RESULTS
  Two of three populations evaluated (P116 and P13) were found to be uniform for resistance (>98% of individuals survived 8.8 g AI ha(-1) of cloransulam), whereas a third population, P525, contained about 85% resistant individuals. Cross-resistance to cloransulam, chlorimuron, imazethapyr and bispyribac was observed in the P116 population. P525 and P13 were both sensitive to imazethapyr but resistant to chlorimuron, imazethapyr and bispyribac. Enzyme activity assays indicated that resistance in P13 was due to an altered target site. Southern blot analysis indicated that the ALS target site is encoded by a single copy gene. Overlapping ALS gene regions were amplified and sequenced from each population. Amino acid substitutions of Ser for Pro at position 197 (P197S) was detected from P13, Ala for Pro (P197A) was identified from P525 and substitution of Glu for Asp (D376E) at position 376 was found in P116. Molecular markers were developed to differentiate between wild-type and resistant codons at positions 197 and 376 of horseweed ALS.
  
  
  CONCLUSIONS
  Resistance to ALS-inhibiting herbicides in horseweed is conferred by target-site mutations that have also been identified in other weed species. Identification of the mutations within horseweed ALS gene sequence enables molecular assays for rapid detection and resistance diagnosis.
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL, USA.
authors.forename: Danman
authors.initials: D
authors.lastname: Zheng
authors.forename: Greg R
authors.initials: GR
authors.lastname: Kruger
authors.forename: Sukhvinder
authors.initials: S
authors.lastname: Singh
authors.forename: Vince M
authors.initials: VM
authors.lastname: Davis
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Tranel
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Weller
authors.forename: William G
authors.initials: WG
authors.lastname: Johnson
mesh_terms: D000095:Acetolactate Synthase / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D001565:Benzoates / Q000494:pharmacology; D015415:Biomarkers / Q000378:metabolism; D015139:Blotting, Southern; D003062:Codon / Q000235:genetics / Q000378:metabolism; D035401:Conyza / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D004789:Enzyme Activation; D057075:Enzyme Assays; D017343:Genes, Plant; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D009154:Mutation; D009539:Nicotinic Acids / Q000494:pharmacology; D057685:Plant Weeds / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D013045:Species Specificity; D058728:Weed Control
chemical_list: D001565:Benzoates; D015415:Biomarkers; D003062:Codon; D006540:Herbicides; D009539:Nicotinic Acids; D011743:Pyrimidines; C093630:imazethapyr; C549011:bispyribac; D000095:Acetolactate Synthase