Diclofop-resistant Lolium rigidum from northern Greece with cross-resistance to ACCase inhibitors and multiple resistance to chlorsulfuron

Repeated use of ACCase- and ALS-inhibiting herbicides in northern Greece ha s resulted in the evolution of a population of Lolium rigidum resistant to diclofop and chlorsulfuron. The biotype hom Athos was highly resistant to d iclofop and also exhibited differential cross-resistance to clodinafop, flu azifop, tralkoxydim and sethoxydim. Assay of ACCase activity confirmed that the resistant biotype was tenfold more resistant to diclofop than the susc eptible biotype, suggesting that the resistance mechanism could involve an altered target site. The diclofop-resistant biotype has also exhibited mult iple resistance to chlorsulfuron and the mechanism for this is unknown. See d-bioassay was found to be a rapid, cheap and reliable method to identify p opulations oft. rigidum resistant to ACCase inhibitors and chlorsulfuron. M oreover, root elongation in the seed bioassay was more sensitive to ACCase inhibitors and chlorsulfuron than shoot elongation. (C) 2000 Society of Che mical Industry.