title: Recurrent selection with reduced 2,4-D amine doses results in the rapid evolution of 2,4-D herbicide resistance in wild radish (Raphanus raphanistrum L.).
abstract: BACKGROUND
  When used at effective doses, weed resistance to auxinic herbicides has been slow to evolve when compared with other modes of action. Here we report the evolutionary response of a herbicide-susceptible population of wild radish (Raphanus raphanistrum L.) and confirm that sublethal doses of 2,4-dichlorophenoxyacetic acid (2,4-D) amine can lead to the rapid evolution of 2,4-D resistance and cross-resistance to acetolactate synthase (ALS)-inhibiting herbicides.
  
  
  RESULTS
  Following four generations of 2,4-D selection, the progeny of a herbicide-susceptible wild radish population evolved 2,4-D resistance, increasing the LD50from 16 to 138 g ha-1. Along with 2,4-D resistance, cross-resistance to the ALS-inhibiting herbicides metosulam (4.0-fold) and chlorsulfuron (4.5-fold) was evident. Pretreatment of the 2,4-D-selected population with the cytochrome P450 inhibitor malathion restored chlorsulfuron to full efficacy, indicating that cross-resistance to chlorsulfuron was likely due to P450-catalysed enhanced rates of herbicide metabolism.
  
  
  CONCLUSIONS
  This study is the first to confirm the rapid evolution of auxinic herbicide resistance through the use of low doses of 2,4-D and serves as a reminder that 2,4-D must always be used at highly effective doses. With the introduction of transgenic auxinic-herbicide-resistant crops in the Americas, there will be a marked increase in auxinic herbicide use and therefore the risk of resistance evolution. Auxinic herbicides should be used only at effective doses and with diversity if resistance is to remain a minimal issue. © 2016 Society of Chemical Industry.
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Ashworth
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Walsh
authors.affiliation: School of Plant Biology, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Ken C
authors.initials: KC
authors.lastname: Flower
authors.affiliation: Australian Herbicide Resistance Initiative, School of Plant Biology, The University of Western Australia, Crawley, WA, Australia. stephen.powles@uwa.edu.au.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Powles
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D005075:Biological Evolution; D004123:Dimethylamines / Q000494:pharmacology; D053209:Herbicide Resistance; D006540:Herbicides / Q000494:pharmacology*; D031224:Raphanus / Q000187:drug effects* / Q000235:genetics; D012641:Selection, Genetic
chemical_list: D004123:Dimethylamines; D006540:Herbicides; C037991:2,4-D amine; D015084:2,4-Dichlorophenoxyacetic Acid
keywords: 2,4-D; Raphanus raphanistrum; evolution; herbicide resistance; low dose; recurrent selection; wild radish