<b>HRAC Group 2</b> <font size='2'> (Legacy B) </font> resistant Bromus tectorum from United States, Montana

International Survey of Herbicide-Resistant Weeds

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Friday, November 1, 2024

HRAC GROUP 2 (LEGACY B) RESISTANT DOWNY BROME (CHEATGRASS)
(Bromus tectorum)

Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)

United States, Montana

INTRODUCTION		DOWNY BROME (CHEATGRASS)
Downy Brome (Cheatgrass) (Bromus tectorum) is a monocot weed in the Poaceae family. In Montana this weed first evolved resistance to Group 2 (Legacy B) herbicides in 2016 and infests Wheat. 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 imazamox, procarbazone-Na, and pyroxsulam 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 Mar 21, 2017 )
Common Name	Downy Brome (Cheatgrass)
Species	Bromus tectorum
Group	Inhibition of Acetolactate Synthase HRAC Group 2 (Legacy B)
Herbicides	imazamox, procarbazone-Na, and pyroxsulam
Location	United States, Montana
Year	2016
Situation(s)	Wheat
Contributors - (Alphabetically)	Prashant Jha, and Vipan Kumar
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ACADEMIC ASPECTS

Confirmation Tests

Greenhouse, and Laboratory trials comparing a known susceptible Downy Brome (Cheatgrass) biotype with this Downy Brome (Cheatgrass) 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 Downy Brome (Cheatgrass) indicate that the inheritance is determined by a one gene trait. 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 2 (Legacy B) resistant Downy Brome (Cheatgrass) from Montana indicate that resistance is due to an altered target site. 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 2 (Legacy B) resistant Downy Brome (Cheatgrass) from Montana please update the database.

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CONTRIBUTING WEED SCIENTISTS

PRASHANT JHA

Associate Professor-Weed Science Montana State University-Bozeman Southern Agricultural Research Center 748 Railroad Highway Huntley, 59037, Montana United States Email Prashant Jha Web : Web Site Link

VIPAN KUMAR

Assistant Professor-Weed Science Kansas State University Agricultural Research Center-Hays 1232 240th Avenue Hays, 67601, Kansas United States Email Vipan Kumar Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Montana have been instrumental in providing you this information. Particular thanks is given to Prashant Jha, and Vipan Kumar for providing detailed information.

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Herbicide Resistant Downy Brome (Cheatgrass) Globally
(Bromus tectorum)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Canada (Alberta)

2021

Canola

glyphosate

Inhibition of Enolpyruvyl Shikimate Phosphate Synthase ( HRAC Group 9 (Legacy G)

France

1981

Corn (maize)

atrazine

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

Spain

1990

Wheat

chlorotoluron

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

Spain

1990

Orchards

simazine

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

United States (Oregon)

1997

Kentucky bluegrass

imazamox, primisulfuron-methyl, and sulfosulfuron

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

United States (Oregon)

2005

Grass seed

clethodim, fluazifop-butyl, quizalofop-ethyl, and sethoxydim

Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)

United States (Montana)

2016

Wheat

imazamox, procarbazone-Na, and pyroxsulam

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

Literature about Similar Cases

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Kumar, V. and P. Jha. 2017. First report of Ser653Asn mutation endowing high-level resistance to imazamox in downy brome (Bromus tectorum L.). Pest Management Science DOI 10.1002/ps.4673 : .

BACKGROUND: Bromus tectorum L. is one of the most troublesome grass weed species in cropland and non-cropland areas ofthe northwestern USA. In summer 2016, a B. tectroum accession (R) that survived imazamox at the ﬁeld-use rate (44 g ha–1)inan imidazolinone-tolerant ( IMI-tolerant or Clearﬁeld™) winter wheat ﬁeld was collected from a wheat ﬁeld in Carter County, MT,USA. The aim of this study was to determine the resistance proﬁle of the B. tectroum R accession to imazamox and other ALSinhibitors, and investigate the mechanism of resistance to imazamox.

RESULTS: The R B. tectorum accession had a high-level resistance (110.1-fold) to imazamox (IMI) and low to moderate-levelscross-resistance to pyroxsulam (TP) (4.6-fold) and propoxycarbazone (SCT) (13.9-fold). The R accession was susceptible tosulfosulfuron (SU) and quizalofop and clethodim (ACCase inhibitors), paraquat (PS I inhibitor), glyphosate (EPSPS inhibitor)and glufosinate (GS inhibitor). Sequence analysis of the ALS gene revealed a single, target-site Ser653Asn mutation in R plants.Pretreatment of malathion followed by imazamox at 44 or 88 g ha–1did not reverse the resistance phenotype.

CONCLUSION: This is the ﬁrst report of evolution of cross-resistance to ALS-inhibiting herbicides in B. tectorum. A single-pointmutation, Ser653Asn, was identiﬁed, conferring the high-level resistance to imazamox.

Calha, Im; Rocha, F; Ruiz-Santaella, Jr; Cruz-Hipolito, He. 2008. Two decades of herbicide resistance in the Iberian Peninsula. Journal Of Plant Diseases And Protection : 79 - 84.

About 20 years ago the first case of herbicide resistance in the Iberian Peninsula was reported: Amaranthus spp. R to atrazine in Spanish orchards. Since then, herbicide resistance has evolved in many weed species. Changes on agricultural practices namely new tillage systems, new rotational programmes, combined with the increased use of herbicides led to the selection of weed biotypes resistant to a wide range of herbicides. Nowadays such a problem affects the most important crops of this Peninsula (maize, wheat, rice, citrus and olive orchards), a spectrum of 26 weed species (14 dicotyledonous and 12 monocotyledonous) with biotypes resistant to several herbicides, namely to ALS inhibitors (Alisma plantago-aquatica, Cyperus difformis, Conyza albida, Aster squamatus, Avena sterilis and Papaver rhoeas), to ACCase inhibitors (Lolium rigidum), to PS II inhibitors (Amaranthus albus, A. blitoides, A. cruentus, A. hybridus, A. retroflexus, Bromus tectorum, Chenopodium album, Conyza bonariensis, C. canadensis, Echinochloa crus-galli, Polygonum lapathifolium, Setaria faberi, S. glauca, S. verticillata, S. viridis and Solanum nigrum), to ureas and amides (B. tectorum and Alopecurus myosuroides), to synthetic auxins (E. crus-galli) and more recently to the herbicide glyphosate (C. bonariensis; L. rigidum and L. multiflorum). Diversity of resistance mechanisms responsible for resistance in this Region involved target site resistance, enhanced rates of herbicide metabolism and multiple resistance. This paper reviews the actual situation in Iberian Peninsula and gives a perspective of adequate strategies for weed management considering the resistance mechanism, the availability of alternative herbicides and other cultural practices.

Ball, D. A. ; Peterson, C. J.. 2007. Herbicide tolerance in imidazolinone-resistant wheat for weed management in the Pacific Northwest U.S.A. : 243 - 250.

Winter wheat ranks high in importance as an agricultural crop in the Pacific Northwest states of Washington, Idaho, and Oregon. Winter annual grass weeds such as jointed goatgrass (Aegilops cylindrica), downy brome (Bromus tectorum), feral rye (Secale cereale), wild oat (Avena fatua) and Italian ryegrass (Lolium multiflorum) have the same life-cycle as winter wheat and are difficult to control in conventional wheat production systems. These weeds annually account for millions of dollars of lost wheat production and reduced quality (i.e. discount by impurities). There has been only moderate success in controlling winter annual grasses in wheat by utilizing multiple-year crop rotations with spring crops and fallow periods, and with chemical control. Selective herbicides have been available for chemical control of downy brome, Italian ryegrass, and wild oat. However, before use of imazamox herbicide with imidazolinone-resistant (CLEARFIELD*) wheat, there was no herbicide that could selectively control jointed goatgrass, feral rye, or volunteer cereals in winter wheat. The first commercial release of an imidazolinone-resistant winter wheat variety in the Pacific Northwest was made during the 2003 growing season. Plant breeders in the Pacific Northwest are continuing to develop imidazolinone-resistant winter wheat varieties adapted to a range of Pacific Northwest production regions. One issue of concern for wheat varietal development is that single-gene tolerance to imazamox in CLEARFIELD* varieties can sometimes show visible crop injury, and possibly, yield reductions in response to herbicide applications. Crop tolerance can vary with time of herbicide application relative to wheat stage of growth, environmental conditions that reduce the wheat plant's ability to metabolize imazamox and, possibly, with specific wheat varieties. A multiple year and location study was conducted to evaluate imazamox tolerance in CLEARFIELD* wheat lines being developed for Pacific Northwest production regions. Results indicate that during specific years and locations, single-gene CLEARFIELD* varieties differed slightly in their relative tolerance to imazamox. The most important determinant of crop tolerance was related to herbicide application rate and timing..

Tominaga, T.. 2007. Germination characteristics of ALS inhibiting herbicides-resistant biotypes of weed. Journal of Weed Science and Technology 52 : 36 - 40.

This overview explains the germination characteristics of ALS inhibition herbicide-resistant biotypes of weed such as Lactuca serriola L., Kochia scoparia L. [Bassia scoparia], Lolium rigidum Gaud., Sisymbrium orientale Torn., Scirpus juncoides Roxb. var. ohwianus T. Koyama and Bromus tectorum L.. Valine, isoleucine and leucine content in the seeds of ALS inhibition herbicide-resistant biotypes are also discussed and the data from Kochia scoparia L. [Bassia scoparia] and Lactuca serriola L. are shown. In the seeds of ALS inhibition herbicide-resistant Kochia scoparia L., valine, isoleucine and leucine content are twice as much as that of ALS herbicide-susceptible variety. Valine, isoleucine and leucine content in the seeds of ALS inhibition herbicide-resistant Lactuca serriola L. are 70%, 9% and 43% higher, respectively, in comparison to that of ALS inhibition herbicide-susceptible variety..

Menendez, J. ; Gonzalez-Gutierrez, J. ; Prado, R. de. 2007. Characterisation of a triazine-resistant biotype of Bromus tectorum found in Spain. Weed Research (Oxford) 47 : 113 - 121.

A population of Bromus tectorum infesting an olive grove at Córdoba (Spain) survived simazine use rates of 3.0 kg a.i. ha^-1 over two consecutive years. Non-tillage olive monoculture and two annual simazine applications had been carried out for 10 years. The resistant biotype showed a higher ED₅₀ value (7.3 kg a.i. ha^-1) than that of the susceptible control (0.1 kg a.i. ha^-1), a 73-fold increase in herbicide tolerance. The use of fluorescence, Hill reaction, absorption, translocation and metabolism assays showed that simazine resistance in this biotype was caused by a modification of the herbicide target site, since chloroplasts from the resistant biotype of B. tectorum were more than 300 times less sensitive to simazine than those from the susceptible biotype. In addition, non-treated resistant plants of B. tectorum displayed a significant reduction in the Q_A to Q_B electron transfer rate when compared with the susceptible biotype, a characteristic that has been linked to several mutations in the protein D1 conferring resistance to PS II inhibiting herbicides. Resistant plants showed cross-resistance to other groups of triazine herbicides with the hierarchy of resistance level being methoxy-s-triazines ≥chloro-s-triazines > methylthio-s-triazines > cis-triazines. The results indicate a naturally occurring target-site point mutation is responsible for conferring resistance to triazine herbicides. This represents the first documented report of target site triazine resistance in this downy brome biotype..

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