HRAC GROUP 2 (LEGACY B) RESISTANT RICEFIELD BULRUSH
(Schoenoplectus mucronatus (=Scirpus mucronatus))

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

Italy

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INTRODUCTION RICEFIELD BULRUSH Ricefield Bulrush (Schoenoplectus mucronatus (=Scirpus mucronatus)) is a monocot weed in the Cyperaceae family.  In Italy this weed first evolved resistance to Group 2 (Legacy B) herbicides in 1995 and infests Rice.   Group 2 (Legacy B) herbicides are known as Inhibition of Acetolactate Synthase (Inhibition of Acetolactate Synthase ).  Research has shown that these particular biotypes are resistant to azimsulfuron, bensulfuron-methyl, cinosulfuron, and ethoxysulfuron and they may be cross-resistant to other Group 2 (Legacy B) 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 May 08, 2014 ) Common Name Ricefield Bulrush Species Schoenoplectus mucronatus (=Scirpus mucronatus) Group Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B) Herbicides azimsulfuron, bensulfuron-methyl, cinosulfuron, and ethoxysulfuron Location Italy Year 1995 Situation(s) Rice Contributors - (Alphabetically) Maurizio Sattin  Edit this Case  |  Add New Case of Resistance  |  Add Note

NOTES ABOUT THIS BIOTYPE AREAS FOUND Maurizio Sattin Novara, Pavia, Vercelli, Milano, Biella Edit this Note  |  Add New Note   GENERAL Maurizio Sattin There is a generalised cross resistance among the sulfonylureas (Azimsulfuron, Bensulfuron- methyl, Cinosulfuron, Ethoxysulfuron) as well as to the triazolopyrimidine (metosulam), but the level of resistance which appears to be very high for the sulfonylurea (the ratios between the GR50 of the resistant and susceptible biotypes are higher than 650) it is, in general, more variable for Metosulam (GR50 varies between 88 to 514). A few populations show very high level of resistance to both sulfonylureas and triazolopyrimidine:. Although there is as yet no direct experimental proof, the available information suggests that the resistance mechanism could be a target-site. It is now estimated that between 10,000 and 15,000 ha are affected. Most resistant populations come from Novara Province and were selected by bensulfuron -methyl. The field histories suggest that resistance developed in a paddy rice monoculture system after at least three-four years using an ALS inhibitor alone for controlling these two species. Generally, resistance has not developed where the weed control strategy is devised in relation to the presence of red rice. Edit this Note  |  Add New Note   GENERAL Roberto Busi Schoenoplectus mucronatus (L.) Palla and Cyperus difformis L. accessions resistant to ALS-inhibitors in Italian rice fields. Vidotto, F; Busi, R; Ferrero, A. Dipartimento di Agronomia, Selvicoltura e Gestione del Territorio. Grugliasco, Italy. Sulfonylureas and other ALS-inhibitor herbicides have been used in Italian paddy fields for more than 10 years. Since 1995, lack of control has been reported for Alisma plantago-aquatica L. and Schoenoplectus mucronatus (L.) Palla. Starting from 1999, insufficient efficacy of ALS-inhibitors herbicides have been reported also against Cyperus difformis L.  A dose-response study has been carried out in the greenhouse to estimate the sensitivity of different S. mucronatus and C. difformis accessions to two bensulfuron-methyl and cinosulfuron.  Two S. mucronatus (RS1 and RS2) and one C. difformis (RC1)accessions that escaped field treatments were sprayed either with bensulfuron-methyl or cinosulfuron at 8 doses, from 0 to 4x the recommended field rate (100 g a.i.ha-1 and 80 g a.i.ha-1 for bensulfuron and cinosulfuron, respectively). Two additional accessions were also included as sensitive references (SS and SC, for S. mucronatus and C. difformis, respectively). Seeds of both species were placed on 36 cm2 pots filled with commercial potting substrate. Prior to seeding, S. mucronatus seeds were scarified with sulphuric acid for 5’. Treatments were applied at 4-leaf stage. Aboveground fresh weight per pot was determined 15-20 days after spraying.   In S. mucronatus, the rate determining 50% of growth reduction (GR50) referred to bensulfuron-methyl and cinosulfuron was more than 1,000 and 100 times higher, respectively, than that of SS, both in RS1 and RS2. In C. difformis, the GR50 of RC1 referred to bensulfuron-methyl was higher than 4x. In the case of cinosulfuron, GR50 of RC1 was more than 700 times higher than that of SC.  The accessions of both species show a variable degree of resistance both to bensulfuron-methyl and cinosulfuron, which are widely used in Italian rice fields. Further investigations are needed to understand the mechanism of resistance. Edit this Note  |  Add New Note

ACADEMIC ASPECTS Confirmation Tests Field, and Greenhouse 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 2 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 The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.   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 2 (Legacy B) resistant Ricefield Bulrush from Italy please update the database.   Edit Case  |  Add Note  |  Add Article  |  Add New Case  |  Help

CONTRIBUTING WEED SCIENTISTS MAURIZIO SATTIN Senior Weed Scientist Italian National Research Council (cnr) IBAF - Weed Science Unit Viale dell'Università 16 Legnaro, 35020, Padova Italy Email Maurizio Sattin

ACKNOWLEDGEMENTS The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Italy have been instrumental in providing you this information. Particular thanks is given to Maurizio Sattin for providing detailed information.

Herbicide Resistant Ricefield Bulrush Globally (Schoenoplectus mucronatus (=Scirpus mucronatus)) Herbicide Resistant Ricefield Bulrush Globally (Schoenoplectus mucronatus (=Scirpus mucronatus)) Drag a column header and drop it here to group by that column Herbicide Resistant Ricefield Bulrush Globally (Schoenoplectus mucronatus (=Scirpus mucronatus)) # Country Country StateName FirstYear Situation Active Ingredients CountryID Site of Action WeedID Species CommonName ResistID 1 Chile Chile   2005 Rice bensulfuron-methyl, bispyribac-sodium, cyclosulfamuron, ethoxysulfuron, imazamox, and pyrazosulfuron-ethyl 8 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 5396 2 Italy Italy   1995 Rice azimsulfuron, bensulfuron-methyl, cinosulfuron, and ethoxysulfuron 24 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 1129 3 United States (California) United States California 1997 Rice bensulfuron-methyl 45 Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 1099 4 United States (California) United States California 2014 Rice propanil 45 PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2) 182 Schoenoplectus mucronatus (=Scirpus mucronatus) Ricefield Bulrush 9924

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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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