INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

CORN POPPY (Papaver rhoeas) with GROUP B/2 resistance: (INHIBITION OF ACETOLACTATE SYNTHASE ) Inhibition of Acetolactate Synthase

MUTATION: PROLINE 197 to HISTIDINE

Corn Poppy (Papaver rhoeas) is a dicot plant in the papaveraceae family. A single amino acid substitution from Proline 197 to Histidine has led to resistance to Inhibition of Acetolactate Synthase as indicated in the table below.		Corn Poppy

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	Susceptible
Triazolinones	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..

Scarabel, L. ; Carraro, N. ; Sattin, M. ; Varotto, S.. 2004. Molecular basis and genetic characterisation of evolved resistance to ALS-inhibitors in Papaver rhoeas. Plant Science 166 : 703 - 709.

ALS gene from susceptible and field-selected Papaver rhoeas populations resistant to ALS-inhibitor herbicides was studied. The full-length cDNA and genomic sequence coding for acetolactate synthase (ALS) of a susceptible population of poppy was cloned and sequenced. Some peculiarities in poppy ALS gene were identified aligning the sequences in GenBank. Southern analysis using a 800 bp fragment of ALS showed that poppy possesses a single copy of the gene. Partial ALS genomic DNAs from nine poppy populations resistant to ALS-inhibitor herbicides and four susceptible populations, collected in central and southern Italy where resistance to ALS-inhibitors is increasing due to repeated use of sulfonylureas, were amplified and sequenced. Comparison of the coding sequences identified three independent point mutations leading to different amino acid substitutions in the deduced polypeptide sequence. The three point mutations, all at proline 197 (CCT) (based on Arabidopsis numbering) in the conserved domain A of the gene, included a change of Pro to His (CAT), to Thr (ACT) or to Ser (TCT). These mutations cause similar cross-resistance patterns. Analysis of the progeny of two crosses between resistant (R) and susceptible (S) biotypes indicated that resistance is inherited as a dominant monogenic trait, although seed dormancy may interfere with a correct segregation of R and S biotypes in the progeny. These are the first mutations completely characterised in poppy ALS gene that confer resistance to ALS-inhibitor herbicides..

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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