Cross-resistance to ACCase inhibitors of Lolium multiflorum, Lolium perenne and Lolium rigidum found in Chile.

APPs (aryloxyphenoxypropionates) and CHDs (cyclohexanediones) are two of the most important groups used post-emergence for the control of grass weeds. They inhibit the lipid synthesis in plants by interfering with the activity of the enzyme Acetyl-coenzyme A carboxylase (ACCase), acting at a meristematic level. The resistance patterns of the biotypes characterized seem to indicate the existence of different degrees of resistance. It is thus possible to identify biotypes presenting cross-resistance only to certain APPs, to APPs and CHDs, or only to CHDs. The objective of this work was to evaluate the cross-resistance to fenoxaprop-P-ethyl, fluazifop-P-butyl, propaquizafop, cyhalofop-butyl, haloxyfop-R-methyl, tralkoxydim and tepraloxydim in three species of Lolium (L. multiflorum, L. perenne, and L. rigidum) resistant to diclofop-methyl. The assays were conducted with petri-dishes in which, over increasing doses, fifty seeds per biotype and dose were located in each dish. Two weeks later, the following parameters were evaluated: germination (%), number of roots, radicle length, plumule length, and fresh weight reduction (%). Based on plumule length and fresh weight reduction (%), diclofop-methyl resistant biotypes showed cross-resistance to fenoxaprop-P-ethyl, fluazifop-P-butyl, cyhalofop-butyl, haloxyfop-R-methyl, but not to propaquizafop, tralkoxydim and tepraloxydim. The parameters germination (%), number of roots or root length did not show a good relation between the dose and its efficacy (curves of dose response) for any of the susceptible and resistant biotypes studied.