title: Glyphosate resistance in Echinochloa colona: phenotypic characterisation and quantification of selection intensity.
abstract: BACKGROUND
  A population of Echinochloa colona infesting agricultural fields in the northern region of Western Australia evolved glyphosate resistance after 10 years of glyphosate selection. This study identified two phenotypic (susceptible S versus resistant R) lines from within a segregating glyphosate-resistant population. Estimation of survival, growth and reproductive rates of the phenotypes in response to glyphosate selection helped to characterise the level of resistance, fitness and the selection intensity for glyphosate in this species.
  
  
  RESULTS
  Estimations of LD(50) (lethal dose) and GR(50) (growth rate) showed an eightfold glyphosate resistance in this population. The resistant index based on the estimation of seed number (SY(n50)) showed a 13-fold resistance. As a result of linear combination of plant survival and fecundity rates, plant fitness values of 0.2 and 0.8 were estimated for the S and R phenotypes when exposed to the low dose of 270 g glyphosate ha(-1). At the recommended dose of 540 g glyphosate ha(-1) , fitness significantly decreased (fivefold) in S plants but remained markedly similar (0.7) in plants of the R phenotype. Thus, the calculated selection intensity (SI) at 540 g glyphosate ha(-1) was much greater (SI = 17) than at 270 g glyphosate ha(-1) (SI = 4).
  
  
  CONCLUSIONS
  The assessment of plant survival and fecundity in response to glyphosate selection in the S and R phenotypes allowed a greater accuracy in the estimation of population fitness of both phenotypes and thus of glyphosate selection intensity in E. colona. The estimation of seed number or mass of phenotypes under herbicide selection is a true ecological measure of resistance with implications for herbicide resistance evolution.
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, WA, Australia.
authors.forename: Sou Sheng
authors.initials: SS
authors.lastname: Goh
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, WA, Australia.|IFEVA-CONICET, Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Martin M
authors.initials: MM
authors.lastname: Vila-Aiub
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, WA, Australia.
authors.forename: Roberto
authors.initials: R
authors.lastname: Busi
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, WA, Australia.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Powles
mesh_terms: D031747:Echinochloa / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D056084:Genetic Fitness; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology; D008136:Longevity; D010641:Phenotype; D057685:Plant Weeds / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D012098:Reproduction; D012641:Selection, Genetic; D014904:Western Australia; D000097797:Glyphosate
chemical_list: D005998:Glycine; D006540:Herbicides; D000097797:Glyphosate
keywords: glyphosate resistance; selection intensity; Echinochloa colona; fitness; fecundity