WILD OAT (Avena fatua) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: SERINE 653 to THREONINE
Wild Oat (Avena fatua) is a monocot plant in the poaceae family. A single amino acid substitution from Serine 653 to Threonine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Wild Oat

Chemical Family	Example Herbicide	Resistance Level
Imidazolinones	Imazethapyr	Resistant > 10 fold
Pyrimidinyl benzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Not Determined
Triazolopyrimidine - Type 1	Chloransulam-methyl	Not Determined
Triazolinones	Flucarbazone-Na	Not Determined

NOTE

The cross-resistance pattern may be obscured by the co-occurrence of non-target-site resistance in the population (see Beckie et al. 2012).

REFERENCES

Beckie, H. J. ; Warwick, S. I. ; Sauder, C. A.. 2012. Basis for herbicide resistance in Canadian populations of wild oat (Avena fatua). Weed Science 60 : 10 - 18.

Wild oat is the second-most abundant, but most economically important, weed across the Canadian Prairies of western Canada. Despite the serious economic effects of resistance to acetyl-CoA carboxylase (ACC) or acetolactate synthase (ALS) inhibitors or both in this weed throughout the Northern Great Plains of North America, little research has examined the basis for herbicide resistance. We investigated target-site and nontarget-site mechanisms conferring ACC- and ALS-inhibitor resistance in 16 wild oat populations from across western Canada (four ACC-inhibitor resistant, four ALS-inhibitor resistant, and eight ACC- and ALS-inhibitor resistant). The ACC1 mutations were found in 8 of the 12 ACC inhibitor-resistant populations. The Ile1781Leu mutation was detected in three populations, the Trp2027Cys and Asp2078Gly mutations were in two populations each, and the Trp1999Cys, Ile2041Asn, Cys2088Arg, and Gly2096Ser substitutions were in one population each. Three populations had two ACC1 mutations. Only 2 of the 12 ALS inhibitor-resistant populations had an ALS target-site mutation - Ser653Thr and Ser653Asn substitutions. This is the first global report of ALS target-site mutations in Avena spp. and four previously undocumented ACC1 mutations in wild oat. Based on these molecular analyses, seedlings of five ACC+ALS inhibitor-resistant populations (one with an ACC1 mutation; four with no ACC or ALS mutations) were treated with malathion, a known cytochrome P450 monooxygenase inhibitor, followed by application of one of four ACC- or ALS-inhibiting herbicides. Malathion treatment often resulted in control or suppression of these populations, suggesting involvement of this enzyme system in contributing to resistance to both ACC and ALS inhibitors..

This case was entered by Patrick Tranel Email: tranel@illinois.edu

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