Acetolactate synthase inhibitor-resistant stinkweed (Thlaspi arvense L.) in Alberta

Two stinkweed populations from southern and central Alberta were not controlled by acetolactate synthase (ALS)-inhibiting herbicides in 2000. This study reports on their cross-resistance to ALS-inhibiting herbicides, molecular basis of resistance, and inheritance of resistance. Both putative herbicide-resistant biotypes responded similarly to increasing doses of the herbicides. The biotypes were highly resistant to ethametsulfuron and exhibited a low level of resistance to metsulfuron and imazethapyr. However, both biotypes were not resistant to florasulam, a triazolopyrimidine ALS inhibitor, or sulfometuron, a non-selective sulfonylurea ALS inhibitor. The cross-resistance pattern was consistent with the confirmed target-site mutation. Sequence analysis of the ALS gene detected a Pro197Leu mutation in both biotypes. Similar to many other ALS inhibitor-resistant weed biotypes, resistance was conferred by a single dominant gene. This study confirms the first global occurrence of herbicide resistance in this species.