<b>HRAC Group 5</b> <font size='2'> (Legacy C1 C2) </font> resistant Schoenoplectus mucronatus (=Scirpus mucronatus) from United States, California

INTERNATIONAL HERBICIDE-RESISTANT WEED DATABASE

HRAC GROUP 5 (LEGACY C1 C2) RESISTANT RICEFIELD BULRUSH
(Schoenoplectus mucronatus (=Scirpus mucronatus))

PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)

United States, California

INTRODUCTION		RICEFIELD BULRUSH
Ricefield Bulrush (Schoenoplectus mucronatus (=Scirpus mucronatus)) is a monocot weed in the Cyperaceae family. In California this weed first evolved resistance to Group 5 (Legacy C1 C2) herbicides in 2014 and infests Rice. Group 5 (Legacy C1 C2) herbicides are known as PSII inhibitors - Serine 264 Binders (Inhbition of Photosynthesis at PSll - Serine 264 Binders ). Research has shown that these particular biotypes are resistant to propanil and they may be cross-resistant to other Group 5 (Legacy C1 C2) herbicides. The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

QUIK STATS (last updated Oct 14, 2014 )
Common Name	Ricefield Bulrush
Species	Schoenoplectus mucronatus (=Scirpus mucronatus)
Group	PSII inhibitors - Serine 264 Binders HRAC Group 5 (Legacy C1 C2)
Herbicides	propanil
Location	United States, California
Year	2014
Situation(s)	Rice
Contributors - (Alphabetically)	Albert Fischer, and Rafael Pedroso
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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Ricefield Bulrush biotype with this Ricefield Bulrush biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on HRAC Group 5 resistant Ricefield Bulrush have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

Studies on the mechanism of resistance of Group 5 (Legacy C1 C2) resistant Ricefield Bulrush from California indicate that resistance is due to enhanced metabolism. There may be a note below or an article discussing the mechanism of resistance in the Fact Sheets and Other Literature

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of Group 5 (Legacy C1 C2) resistant Ricefield Bulrush from California please update the database.

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CONTRIBUTING WEED SCIENTISTS

ALBERT FISCHER

Professor University Of California Department of Plant Sciences Weed Ecophysiology Mail Stop #4 279/279A Robbins Hall Davis, 95616, California United States Email Albert Fischer Web : Web Site Link

RAFAEL PEDROSO

PhD Student and Graduate Student Researcher University of California at Davis Plant Sciences One Shields Avenue Davis, 95616, California United States Email Rafael Pedroso Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in California have been instrumental in providing you this information. Particular thanks is given to Albert Fischer, and Rafael Pedroso for providing detailed information.

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Herbicide Resistant Ricefield Bulrush Globally
(Schoenoplectus mucronatus (=Scirpus mucronatus))

Country

FirstYear

Situation

Active Ingredients

Site of Action

Chile

2005

Rice

bensulfuron-methyl, bispyribac-sodium, cyclosulfamuron, ethoxysulfuron, imazamox, and pyrazosulfuron-ethyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Italy

1995

Rice

azimsulfuron, bensulfuron-methyl, cinosulfuron, and ethoxysulfuron

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (California)

1997

Rice

bensulfuron-methyl

Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United States (California)

2014

Rice

propanil

PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)

Literature about Similar Cases

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Scarabel, L. ; Locascio, A. ; Furini, A. ; Sattin, M. ; Varotto, S.. 2010. Characterisation of ALS genes in the polyploid species Schoenoplectus mucronatus and implications for resistance management. Pest Management Science 66 : 337 - 344.

BACKGROUND: The polyploid weed Schoenoplectus mucronatus (L.) Palla has evolved target-site resistance to ALS-inhibiting herbicides in Italian rice crops. Molecular and genetic characterisation of the resistance mechanism is relevant to the evolution and management of herbicide resistance. The authors aimed (a) to study the organisation of the target-site loci in two field-selected S. mucronatus populations with different cross-resistance patterns, (b) to identify the mutations endowing resistance to ALS inhibitors and determine the role of these mutations by using transgenesis and (c) to analyse the implications for the management of the S. mucronatus populations. RESULTS: Two complete ALS genes (ALS1 and ALS2) having an intron and a third partial intronless ALS gene (ALS3) were identified. The presence of multiple ALS genes was confirmed by Southern blot analyses, and ALS loci were characterised by examining cytosine methylation. In S. mucronatus leaves, the transcripts of ALS1, ALS2 and ALS3 were detected. Two mutations endowing resistance (Pro₁₉₇ to His and Trp₅₇₄ to Leu) were found in both resistant populations, but at different frequencies. Tobacco plants transformed with the two resistant alleles indicated that the Pro₁₉₇-to-His substitution conferred resistance to SU and TP herbicides, while the allele with the Trp₅₇₄-to-Leu substitution conferred cross-resistance to SU, TP, IMI and PTB herbicides. CONCLUSION: Schoenoplectus mucronatus has multiple ALS genes characterised by methylated sites that can influence the expression profile. The two mutated alleles proved to be responsible for ALS resistance. At population level, the resistance pattern depends on the frequency of various resistant genotypes, and this influences the efficacy of various ALS-inhibiting herbicides..

Tabacchi M, Scarabel L, Sattin M. 2004. Herbicide Resistance in Italian Rice Crops: A Late-Developing but Fast-Evolving Story. Med Rice Conference, Torino - Italy. 13th to 15th February 2004 : .

Herbicides have been used intensively in Italian rice crops for the last 40 years. Use of ALS-inhibitors began in 1988 and now more than 80% of rice fields are treated with these herbicides. Since 1994, three species (Alisma plantago-aquatica, Schoenoplectus mucronatus and Cyperus difformis) have evolved resistance to ALS inhibitors, while three populations of Echinochloa crus-galli have evolved resistance to propanil. A population of Echinochloa erecta recently proved to be multiple-resistant to quinclorac and propanil. It is estimated that resistance exists in more than 25,000 ha, with S. mucronatus and C. difformis showing the highest rate of increase. Field histories show that high selection pressure had been imposed for several years prior to resistance development, as well as a lack of any resistance prevention strategy. Most ALS-resistant populations show a wide pattern of cross-resistance with a high level of resistance to SU and a lower level to the TP metosulam.

Sattin, M. ; Zanin, G.. 2003. The situation of herbicide resistant weeds in Italy. Informatore Fitopatologico 53 : 24 - 27.

In Italy, 12 weed species (Amaranthus cruentus, Solanum nigrum, Chenopodium album, Avena sterilis subsp. ludoviciana, Alisma plantago-aquatica, Schoenoplectus mucronatus, Lolium spp., Papaver rhoeas, Phalaris paradoxa, Amaranthus retroflexus, Cyperus difformis and Echinochloa crus-galli) have evolved populations resistant to herbicides, although to date, the areas involved are quite limited. The cropping systems where resistance has developed are mainly monocultures (e.g. rice and durum wheat) or where short crop rotations are used. The herbicides involved are acetyl-CoA carboxylase inhibitors, acetolactate synthase inhibitors and PSII inhibitors. A brief history of herbicide resistance in Italy is presented and the major resistance management techniques for preventing its appearance and spread are outlined. Integrated weed management appears to be the best solution..

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