PERENNIAL RYEGRASS (Lolium perenne) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase
MUTATION: ASPARTATE 376 to GLUTAMATE
Perennial Ryegrass (Lolium perenne) is a monocot plant in the poaceae family. A single amino acid substitution from Aspartate 376 to Glutamate has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Perennial Ryegrass

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

REFERENCES

Menegat, A., G. C. Bailly, R. Aponte, G. M. T. Heinrich, B. Sievernich, and R. Gerhards. 2016. Acetohydroxyacid synthase (AHAS) amino acid substitution Asp376Glu in Lolium perenne: effect on herbicide efficacy and plant growth.. J Plant Dis Prot DOI 10.1007/s41348-016-0023-2 : .

Recently, the acetohydroxyacid synthase (AHAS) amino acid substitution Asp376Glu was detected in a Lolium perenne  population originating in France. This is the first documented occurrence of the Asp376Glu single- nucleotide polymorphism in a Lolium  species. The effects on herbicide efficacy and plant fitness are presented. Separation of the original population into different genetic subgroups allowed the comparison of different L. perenne  AHAS genotypes according to their susceptibility to AHAS-inhibiting herbicides. Root and shoot biomass accumulation as well as tiller production was analysed for resistant and sensitive populations. Genotype-specific AHAS activity and inhibition were studied in vitro, using recombinant Arabidopsis thaliana  DNA. Plants expressing the AHAS Asp376Glu genotype were resistant against mesosulfuron ?  iodosulfuron, pyroxsulam and propoxycarbazone. To imazamox, reduced susceptibility for dosages below 140 g a.i. ha-1  was observed. In the absence of herbicide, no significant impact of the Asp376Glu genotype on shoot biomass and tiller accumulation could be observed, whereas root biomass of the Asp376Glu genotype was significantly reduced by 68 % compared to the AHAS genetic wild type. The AHAS enzyme study revealed reduced AHAS enzyme rate of 48 % for the Asp376Glu genotype compared to the AHAS genetic wild type. This study highlights the role of the amino acid exchange on resistance profile against the most relevant AHAS-inhibiting herbicides. First indications were found that fitness of the Asp376Glu genotype is hampered..

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

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