RIGID RYEGRASS (Lolium rigidum) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: PROLINE 197 to ARGININE
Rigid Ryegrass (Lolium rigidum) is a monocot plant in the poaceae family. A single amino acid substitution from Proline 197 to Arginine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Rigid Ryegrass

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

REFERENCES

Yu Qin ; Han HePing ; Powles, S. B.. 2008. Mutations of the ALS gene endowing resistance to ALS-inhibiting herbicides in Lolium rigidum populations. Pest Management Science 64 : 1229 - 1236.

BACKGROUND: In the important grass weed Lolium rigidum (Gaud.), resistance to ALS-inhibiting herbicides has evolved widely in Australia. The authors have previously characterised the biochemical basis of ALS herbicide resistance in a number of L. rigidum biotypes and established that resistance can be due to a resistant ALS and/or enhanced herbicide metabolism. The purpose of this study was to identify specific resistance-endowing ALS gene mutation(s) in four resistant populations and to develop PCR-based molecular markers. RESULTS: Six resistance-conferring ALS mutations were identified: Pro-197-Ala, Pro-197-Arg, Pro-197-Gln, Pro-197-Leu, Pro-197-Ser and Trp-574-Leu. All six mutations were found in one population (WLR1). Each Pro-197 mutation conferred resistance to the sulfonylurea (SU) herbicide sulfometuron, whereas the Trp-574-Leu mutation conferred resistance to both sulfometuron and the imidazolinone (IMS) herbicide imazapyr. A derived cleaved amplified polymorphic sequences (dCAPS) marker was developed for detecting resistance mutations at Pro-197. Furthermore, cleaved amplified polymorphic sequences (CAPS) markers were developed for detecting each of the six mutant resistant alleles. Using these markers, the authors revealed diverse ALS-resistant alleles and genotypes in these populations and related them directly to phenotypic resistance to ALS-inhibiting herbicides. CONCLUSION: This study established the existence of a diversity of ALS gene mutations endowing resistance in L. rigidum populations: 1-6 different mutations were found within single populations. At field herbicide rates, resistance profiles were determined more by the specific mutation than by whether plants were homo- or heterozygous for the mutation..

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

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