Diclofop-methyl resistance in populations of Lolium spp. from central Italy

Populations of Lolium spp. collected in central Italy were screened for res istance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides and compared with known susceptible and resistant Lolium rigidum (Gaud.) popul ations from Australia. Populations Roma'94 and Tuscania'97 were up to 8- an d 7.5-fold more resistant to diclofop-methyl, respectively, than susceptibl e populations in pot experiments. However, populations Tarquinia'97 and Vet ralla'94 were not resistant. Diclofop-methyl resistance levels in the Itali an populations were lower than in the Australian populations SLR31 and WLR9 6 (16.5 and > 64 times more resistant than S respectively). In an agar germ ination test, Tuscania'97 showed low levels of cross-resistance to fluazifo p-p-butyl, whereas no cross-resistance was found in the Roma'94 population.