INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

CORN POPPY (Papaver rhoeas) with GROUP B/2 resistance: (ALS INHIBITORS) Inhibition of Acetolactate Synthase

MUTATION: PROLINE 197 to LEUCINE

Corn Poppy (Papaver rhoeas) is a dicot plant in the papaveraceae family. A single amino acid substitution from Proline 197 to Leucine has led to resistance to ALS inhibitors as indicated in the table below.		Corn Poppy

Chemical Family	Example Herbicide	Resistance Level
Imidazolinones	Imazethapyr	Resistant > 10 fold
Pyrimidinylthiobenzoates	Bispyribac-Na	Not Determined
Sulfonylureas	Chlorsulfuron	Resistant > 10 fold
Triazolopyrimidines	Chloransulam-methyl	Susceptible
Sulfonylaminocarbonyltriazolinone	Flucarbazone-Na	Not Determined

REFERENCES

Marshall, R. ; Hull, R. ; Moss, S. R.. 2010. Target site resistance to ALS inhibiting herbicides in Papaver rhoeas and Stellaria media biotypes from the UK. Weed Research (Oxford) 50 : 621 - 630.

Acetolactate synthase (ALS) inhibiting herbicides play an important role in controlling broad-leaved weeds. Biotypes of Stellaria media and Papaver rhoeas showing resistance to ALS inhibiting sulfonylurea herbicides (e.g. metsulfuron) were first identified in 2000 and 2001, respectively, in the UK. Recent work has shown that resistance in both species is due to mutation of the ALS gene conferring an altered herbicide binding site. Three P. rhoeas test biotypes from three areas possessed ALS gene point mutations (Pro-197-Leu or Pro-197-His) conferring ALS target site resistance. All were highly resistant to the sulfonylurea herbicides metsulfuron-methyl and tribenuron-methyl. Several alternative herbicides were tested against resistant P. rhoeas, with MCPA and ioxynil+bromoxynil being most effective. Four resistant biotypes of S. media were identified from widely separated locations. Two different mutations conferring ALS target site resistance were confirmed in two of these biotypes. A mutation conferring Pro-197-Gln substitution in a biotype from Perthshire was associated with resistance to metsulfuron, but not to florasulam. A mutation conferring Trp-574-Leu substitution in the biotype from Aberdeenshire conferred resistance to both herbicides. This is the first characterisation of ALS gene point mutations in resistant S. media. Currently, there are good alternatives for control of resistant biotypes, including fluroxypyr and mecoprop-P. The potential loss of alternative modes of action, as a consequence of reforms to the regulatory system for pesticides in the EU, represents one of the main threats to continued control of ALS resistant S. media..

Kaloumenos, N. S. ; Dordas, C. A. ; Diamantidis, G. C. ; Eleftherohorinos, I. G.. 2009. Multiple Pro197 substitutions in the acetolactate synthase of corn poppy (Papaver rhoeas) confer resistance to tribenuron. Weed Science 57 : 362 - 368.

Variations in the acetolactate synthase (ALS) gene sequence were determined from 28 populations of corn poppy resistant (R) to tribenuron and from 6 populations susceptible (S) to this herbicide. The ALS gene fragment (634 bp) sequence revealed in R populations five point mutations at the codon Pro₁₉₇, and among them the substitution of Pro₁₉₇ by Ala was the most common. The sequencing chromatograms revealed that nine R individuals had only the mutant ALS gene and were homozygous (RR), 18 R individuals had both the wild type and the mutant ALS gene and were heterozygous (RS), whereas one R individual was heterozygous but with two different mutant ALS alleles (R₁R₂). The use of restriction digestion profile analysis to verify the DNA sequence results by detecting the existence of point mutations at the codon 197 managed to distinguish the R and S alleles and confirmed the results obtained from the sequencing chromatograms analysis. The secondary protein structure prediction suggested the formation of novel β-strands for each of the five mentioned amino acid substitutions that was not present in wild type ALS around the mutant site. These findings support the hypothesis that the substitution of Pro₁₉₇ by Ser, Thr, Ala, Arg, or Leu resulted in altered secondary structure, which stabilizes an ALS tertiary conformation that prevents tribenuron binding and thus confers resistance to this herbicide..

Délye, C., F. Pernin, And L. Scarabel.. 2011. Evolution and diversity of the mechanisms endowing resistance to herbicides inhibiting acetolactate-synthase (ALS) in corn poppy (Papaver rhoeas L.). Plant Science 180 : 333 - 342.

We investigated the diversity of mechanisms conferring resistance to herbicides inhibiting acetolactate synthase (ALS) in corn poppy (Papaver rhoeas L.) and the processes underlying the selection for resistance. Six mutant ALS alleles, Arg197, His197, Leu197, Ser197, Thr197 and Leu574 were identified in five Italian populations. Different alleles were found in a same population or a same plant. Comparison of individual plant phenotype (herbicide sensitivity) and genotype (amino-acid substitution(s) at codon 197) showed that all mutant ALS alleles conferred dominant resistance to the field rate of the sulfonylurea tribenuron and moderate or no resistance to the field rate of the triazolopyrimidine florasulam. Depending on the allele, dominant or partially dominant resistance to the field rate of the imidazolinone imazamox was observed. Putative non-target-site resistance mechanisms were also likely present in the populations investigated. The derived Cleaved Amplified Polymorphic Sequence assays targeting ALS codons crucial for herbicide sensitivity developed in this work will facilitate the detection of resistance due to mutant ALS alleles. Nucleotide variation around codon 197 indicated that mutant ALS alleles evolved by multiple, independent appearances. Resistance to ALS inhibitors in P. rhoeas clearly evolved by redundant evolution of a set of mutant ALS alleles and likely of non-target-site mechanisms.

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

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