Target-site resistance to ALS-inhibiting herbicides in Amaranthus palmeri from Argentina

VALERIA PALMIERI; DANIEL TUESCA; ALVARO LARRAN; LUCAS LIEBER; VALERIA PEROTTI; HUGO PERMINGEAT

Urbana-Champaign

Simposio; Plant Science Symposium UIUC 2017; 2017

Herbicide resistant weeds are a serious problem worldwide. Recently, two populations of Amaranthus palmeri with suspected cross-resistance to ALS-inhibiting herbicides (R1 and R2) were found by farmers in two locations from Argentina (Vicuña Mackenna and Totoras, respectively). We conducted studies to confirm and elucidate the mechanism of resistance. Through in vivo dose-response assays, we confirmed both populations had a strong resistance to chlorimuron-ethyl, diclosulam and imazethapyr when compared to a susceptible population (S). The resistance factors (Rf) were > 9.3 and > 11 for GR50 and LD50, respectively. In vitro ALS activity inhibition tests only indicated a considerable resistance to imazethapyr and chlorimuron-ethyl, indicating that other non-target mechanisms could be involved in diclosulam resistance. Subsequently, molecular analysis of als nucleotide sequences revealed three single base-pair mutations conferring substitutions in amino acids previously associated with resistance to ALS inhibitors, A122, W574, and S653. This is the first report of als resistant alleles in Amaranthus palmeri from Argentina. The data support the involvement of a target-site mechanism of resistance to ALS inhibiting herbicides.