SILKY WINDGRASS (Apera spica-venti) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to ASPARAGINE
Silky Windgrass (Apera spica-venti) is a monocot plant in the poaceae family. A single amino acid substitution from Proline 197 to Asparagine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Silky Windgrass

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

REFERENCES

Massa, D., B. Krenz, And R. Gerhards. 2011. Target-site resistance to ALS-inhibiting herbicides in Apera spica-venti populations is conferred by documented and previously unknown mutations. Weed Research 51 : 294 - 303.

In this study, whole-plant bioassays were performed on 72 Apera spica-venti populations that have survived application of acetolactate synthase (ALS)-inhibiting herbicides in recent years. Molecular genetic analysis of the ALS gene revealed a Thr mutation at Pro197 within 67 populations. Sequencing of the whole ALS gene from wild-type and resistant plants not carrying the above-mentioned mutation revealed the presence of a Leu mutation at Trp574 within two populations and an Asn mutation at Pro197 within two populations. As the Pro197-Asn amino acid substitution is reported for the first time in a field-selected weed population, a Cleaved Amplified Polymorphic Sequences (CAPS) marker was developed for its quick detection. In addition, one novel mutation was found within a population that coded for a His substitution at Arg377. Enzyme assays confirmed a significant reduction in inhibition of ALS activity compared with the wild type. This population showed resistance to sulfonylureas (SUs) and cross-resistance to sulfonylaminocarbonyltriazolinones (SCTs) and triazolopyrimidines (TPs) within the whole-plant bioassays. ALS protein sequence alignments from weedy and cultural plants revealed that the Arg377 is highly conserved among known wild-type enzymes. In agreement with existing literature concerning the structure and mechanisms of inhibition of plant ALS, this mutation is probably involved in target-site resistance to ALS inhibitors. Our results suggest that further single-nucleotide polymorphisms impairing proper herbicide performance might be selected within field populations in the near future, making the short- and long-range evolution of target-site resistance difficult to predict depending solely on herbicide use history.

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

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