<b>HRAC Group 1</b> <font size='2'> (Legacy A) </font> resistant Alopecurus myosuroides from France

International Survey of Herbicide-Resistant Weeds

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Saturday, December 28, 2024

HRAC GROUP 1 (LEGACY A) RESISTANT BLACKGRASS
(Alopecurus myosuroides)

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

France

INTRODUCTION		BLACKGRASS
Blackgrass (Alopecurus myosuroides) is a monocot weed in the Poaceae family. In France this weed first evolved resistance to Group 1 (Legacy A) herbicides in 1993 and infests Wheat. Group 1 (Legacy A) herbicides are known as Inhibition of Acetyl CoA Carboxylase (Inhibition of Acetyl CoA Carboxylase ). Research has shown that these particular biotypes are resistant to clodinafop-propargyl, cycloxydim, diclofop-methyl, fenoxaprop-ethyl, haloxyfop-methyl, and sethoxydim and they may be cross-resistant to other Group 1 (Legacy A) 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 Nov 10, 2012 )
Common Name	Blackgrass
Species	Alopecurus myosuroides
Group	Inhibition of Acetyl CoA Carboxylase HRAC Group 1 (Legacy A)
Herbicides	clodinafop-propargyl, cycloxydim, diclofop-methyl, fenoxaprop-ethyl, haloxyfop-methyl, and sethoxydim
Location	France
Year	1993
Situation(s)	Wheat
Contributors - (Alphabetically)	Christophe Délye, and Jacques Gasquez
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NOTES ABOUT THIS BIOTYPE

AREAS FOUND

Jacques Gasquez

Almost everywhere in the area of the species, but mostly in the north of France.

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AREAS FOUND

Christophe Délye

This report does not concerns a given biotype, but is an overview of extensive black-grass sampling (more than 100 locations) in France in 2000.

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BIOASSAYS

Christophe Délye

Resistance diagnosis: via seed-based bioassay and PCR-based assays (target-site based resistance).

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GENERAL

Christophe Délye

seful references (sorry, could not upload some of them due to security access problems - just e-mail if interested) °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° C. Délye, É. Calmès et A. Matéjicek, 2002. SNP markers for black-grass (Alopecurus myosuroides Huds.) genotypes resistant to acetyl CoA-carboxylase inhibiting herbicides. Theoretical and Applied Genetics 104, 1114-1120. °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° C. Délye, A. Matéjicek et J. Gasquez, 2002. PCR-based detection of resistance to Acetyl-Co A carboxylase-inhibiting herbicides in black-grass (Alopecurus myosuroides Huds.) and ryegrass (Lolium rigidum Gaud.). Pest Management Science 58, 474-478. °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° C. Délye, X.-Q. Zhang, C. Chalopin, S. Michel et S. B. Powles, 2003. An isoleucine residue within the carboxyl-transferase domain of multidomain acetyl-CoA carboxylase is a major determinant of sensitivity to aryloxyphenoxypropionate but not to cyclohexanedione inhibitors. Plant Physiology 132, 1716-1723. °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° C. Délye, C. Straub, A. Matéjicek et S. Michel, 2004. Multiple origins for black-grass (Alopecurus myosuroides Huds.) target site-based resistance to herbicides inhibiting acetyl-Co A carboxylase. Pest Management Science 60, 35-41. °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° A. Letouzé A, J. Gasquez J, 2003. Enhanced activity of several herbicide-degrading enzymes: a suggested mechanism responsible for multiple resistance in black-grass (Alopecurus myosuroides Huds.) Agronomie 23, 601-608

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GENERAL

Jacques Gasquez

Comments: this resistance is regularly increasing since 1993 through an annual survey of our working group. We have now a lot of observations which allow us to say that there are several mechanisms of resistance : detoxification (perhaps several) target mutation these different mechanisms may appear in several populations, in several plants of a population or in the same plant. The estimate number of sites and acres infested correspond to 1997.

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MECHANISM

Christophe Délye

DETOXICATION-BASED RESISTANCE is under complex genetic determinism, involving both GST(s) and / or P450(s) TARGET-SITE BASED resistance is governed by several mutant alleles of ACCase. Two of them have been extensively studied, and PCR-based diagnosis assays developed. The two mutant alleles of ACCase confer distinct cross-resistance patterns. They are widespread among black-grass populations. Other alleles are currently studied.

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ONGOING RESEARCH

Christophe Délye

TARGET-BASED RESISTANCE: searching for new ACCase mutations conferring resistance, and developing molecular detection tools. SPREAD OF RESISTANCE: Population genetics studies using selected (ACCase-based) and neutral markers are on the way at the scale of a French Département to understand resistance gene flow within and between black-grass populations. METABOLISATION-BASED RESISTANCE: well, we are thinking about starting studying it, but it is quite a complex problem...

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ACADEMIC ASPECTS

Confirmation Tests

Field, Greenhouse, and Laboratory trials comparing a known susceptible Blackgrass biotype with this Blackgrass 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 1 resistant Blackgrass indicate that the inheritance is determined by a multigenic, dominant, nuclear 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 1 (Legacy A) resistant Blackgrass from France indicate that resistance is due to an altered target site, and 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 1 (Legacy A) resistant Blackgrass from France please update the database.

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CONTRIBUTING WEED SCIENTISTS

CHRISTOPHE DÉLYE

Chargé de Recherches INRA Agroécologie 17 rue de Sully Dijon, F-21000, Burgundy France Email Christophe Délye Web : Web Site Link

JACQUES GASQUEZ

Chargé de Recherches Inra Laboratoire De Malherbologie 702 Hickory Ct Dijon, 21034, Cedex France Email Jacques Gasquez Web : Web Site Link

ACKNOWLEDGEMENTS
The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in France have been instrumental in providing you this information. Particular thanks is given to Christophe Délye, and Jacques Gasquez for providing detailed information.

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Herbicide Resistant Blackgrass Globally
(Alopecurus myosuroides)

Country

FirstYear

Situation

Active Ingredients

Site of Action

Belgium

1996

Winter wheat

clodinafop-propargyl, and fenoxaprop-ethyl

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

Belgium

1996

Wheat

isoproturon

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

Belgium

1996

Winter wheat

atrazine, chlorotoluron, clodinafop-propargyl, fenoxaprop-ethyl, flupyrsulfuron-methyl-Na, pendimethalin, and propaquizafop

Multiple Resistance: 4 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
Inhibition of Microtubule Assembly ( HRAC Group 3 (Legacy K1)

Czech Republic

2008

Wheat

chlorsulfuron

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

Denmark

2001

Winter wheat

fenoxaprop-ethyl

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

Denmark

2001

Winter wheat

clodinafop-propargyl, cycloxydim, fenoxaprop-ethyl, florasulam, flupyrsulfuron-methyl-Na, iodosulfuron-methyl-Na, mesosulfuron-methyl, pendimethalin, and pyroxsulam

Multiple Resistance: 3 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
Inhibition of Microtubule Assembly ( HRAC Group 3 (Legacy K1)

France

1993

Wheat

clodinafop-propargyl, cycloxydim, diclofop-methyl, fenoxaprop-ethyl, haloxyfop-methyl, and sethoxydim

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

France

2003

Wheat

clodinafop-propargyl, diclofop-methyl, fenoxaprop-ethyl, iodosulfuron-methyl-Na, mesosulfuron-methyl, and sethoxydim

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

France

2006

Wheat

imazamethabenz-methyl, iodosulfuron-methyl-Na, and mesosulfuron-methyl

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

France

2020

Cereals, and Rapeseed

flufenacet, and prosulfocarb

Very Long-Chain Fatty Acid Synthesis inhibitors ( HRAC Group 15 (Legacy K3 N)

France

2022

Wheat

glyphosate

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

Germany

1983

Sugar beets, and Wheat

chlorotoluron, fenoxaprop-ethyl, and isoproturon

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)

Germany

2001

Wheat

flupyrsulfuron-methyl-Na

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

Germany

2003

Sugar beets, and Winter wheat

clethodim, cycloxydim, fenoxaprop-ethyl, and fluazifop-butyl

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

Germany

2007

Wheat

chlorotoluron, fenoxaprop-ethyl, flufenacet, isoproturon, mesosulfuron-methyl, and pinoxaden

Multiple Resistance: 4 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)
Very Long-Chain Fatty Acid Synthesis inhibitors ( HRAC Group 15 (Legacy K3 N)

Germany

2009

Cereals

cycloxydim, fenoxaprop-ethyl, flupyrsulfuron-methyl-Na, mesosulfuron-methyl, and pinoxaden

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Ireland

2021

Wheat

cycloxydim, iodosulfuron-methyl-Na, mesosulfuron-methyl, and propaquizafop

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Israel

1979

Roadsides

methabenzthiazuron

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

Italy

2009

Durum wheat

clodinafop-propargyl, fenoxaprop-ethyl, and pinoxaden

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

Netherlands

1989

Wheat

chlorotoluron

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

Netherlands

1996

Winter wheat

chlorotoluron, clodinafop-propargyl, fenoxaprop-ethyl, and isoproturon

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)

Netherlands

1999

Winter wheat

clodinafop-propargyl, cycloxydim, fenoxaprop-ethyl, and penoxsulam

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Netherlands

2010

Winter wheat

florasulam, iodosulfuron-methyl-Na, mesosulfuron-methyl, and pyroxsulam

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

Poland

2010

Winter wheat

iodosulfuron-methyl-Na, and mesosulfuron-methyl

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

Poland

2011

Winter wheat

fenoxaprop-ethyl, and pinoxaden

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

Poland

2012

Winter wheat

fenoxaprop-ethyl, iodosulfuron-methyl-Na, mesosulfuron-methyl, pinoxaden, and sulfometuron-methyl

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Spain

1991

Wheat

chlorotoluron

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

Spain

2015

Canola, Faba beans, Peas, Wheat, and Winter barley

chlorotoluron, clodinafop-propargyl, cloransulam-methyl, iodosulfuron-methyl-Na, isoproturon, mesosulfuron-methyl, and pinoxaden

Multiple Resistance: 3 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
PSII inhibitors - Serine 264 Binders ( HRAC Group 5 (Legacy C1 C2)

Sweden

2011

Winter wheat

clodinafop-propargyl, cycloxydim, and fenoxaprop-ethyl

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

Sweden

2011

Wheat

fenoxaprop-ethyl, flupyrsulfuron-methyl-Na, prosulfocarb, and pyroxsulam

Multiple Resistance: 3 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)
Very Long-Chain Fatty Acid Synthesis inhibitors ( HRAC Group 15 (Legacy K3 N)

Sweden

2014

Spring wheat, Winter barley, and Winter wheat

cycloxydim, fenoxaprop-ethyl, flupyrsulfuron-methyl-Na, iodosulfuron-methyl-Na, mesosulfuron-methyl, and pyroxsulam

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

Switzerland

1997

Wheat, and Winter barley

chlorotoluron, and isoproturon

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

Switzerland

2019

Wheat, and Winter barley

chlorotoluron, iodosulfuron-methyl-Na, mesosulfuron-methyl, and quizalofop-ethyl

Turkey

2001

Wheat

clodinafop-propargyl

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

Turkey

2008

clodinafop-propargyl, and pyroxsulam

Multiple Resistance: 2 Sites of Action
Inhibition of Acetyl CoA Carboxylase ( HRAC Group 1 (Legacy A)
Inhibition of Acetolactate Synthase ( HRAC Group 2 (Legacy B)

United Kingdom

1982

Canola, Cereals, and Wheat

clethodim, clodinafop-propargyl, cycloxydim, diclofop-methyl, fenoxaprop-ethyl, fluazifop-butyl, pinoxaden, quizalofop-ethyl, and sethoxydim

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

United Kingdom

1982

Cereals

chlorotoluron, and isoproturon

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

United Kingdom

1984

Wheat

chlorsulfuron, flupyrsulfuron-methyl-Na, imazamethabenz-methyl, iodosulfuron-methyl-Na, mesosulfuron-methyl, propoxycarbazone-Na, and pyroxsulam

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

United Kingdom

1987

Wheat

pendimethalin

Inhibition of Microtubule Assembly ( HRAC Group 3 (Legacy K1)

Literature about Similar Cases

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Rosenhauer, M. ; Jaser, B. ; Felsenstein, F. G. ; Petersen, J.. 2013. Development of target-site resistance (TSR) in Alopecurus myosuroides in Germany between 2004 and 2012. Journal of Plant Diseases and Protection 120 : 179 - 187.

Alopecurus myosuroides is one of the most important grass weeds on arable land in Germany. For many years, it has developed herbicide-resistant populations. ACCase- and ALS-inhibiting herbicides, in particular, have lost significant efficacy. Two different mechanisms are commonly known to confer resistance to herbicides: target-site resistance (TSR) and non-target-site resistance (NTSR). In Germany, onlyapproximately 5 to 10% of the herbicide-resistant black-grasspopulations have been reported to show TSR so far. To quantify the status and the distribution of TSR in Germany, 653 black-grass samples were collected between 2004 and 2012 all over the country. The samples were tested by bioassays and genetic analysis. Averaged over all tested samples, ACCase-TSR increased from 5.0% in 2004 to 54.3% in 2011. In 2012, the proportion of ACCase-TSR was lower than the previous years (38.5%). Similarly, ALS-TSR rose from 0.8% in 2007 to 13.9% in 2012. Regions with a high density of resistant black-grass samples were identified in the north and south of Germany. The data suggest a rapidly working selection of herbicide-resistant populations which may be due to current agricultural practices and the increasing use of herbicides acting on a single site..

Kaiser, Y. I. ; Menegat, A. ; Gerhards, R.. 2013. Chlorophyll fluorescence imaging: a new method for rapid detection of herbicide resistance in Alopecurus myosuroides. Weed Research (Oxford) 53 : 399 - 406.

Due to the steadily increasing number of putative herbicide-resistant weed populations, the demand for rapid in-season tests is rising. In this study, we introduce a new quantitative herbicide-resistance test system based on chlorophyll fluorescence imaging analysis of photosynthesis-related parameters. Susceptible and herbicide-resistant populations of Alopecurus myosuroides (black-grass) were cultivated in multiwell tissue culture plates containing nutrient agar and different dosages of fenoxaprop-P-ethyl and mesosulfuron+iodosulfuron. The maximum quantum efficiency of the PSII was measured 3 h after transplanting (HAT) and then for seven days every 24 h. Data of maximum quantum efficiency of the PSII were compared with standard whole-plant pot tests and molecular tests for target-site mutations. It was possible to fit dose-response curves and calculate corresponding resistance factors for ED90 for all populations tested using the chlorophyll fluorescence imaging. It was possible to distinguish between resistant and susceptible populations. The results of the chlorophyll fluorescence imaging corresponded well with the standard whole-plant pot tests in the glasshouse. However, populations with proved target-site mutations did not differ from other herbicide-resistant populations in the maximum quantum efficiency values of the PSII. We conclude that the chlorophyll fluorescence imaging provides reliable data on herbicide resistance for both modes of action tested in a shorter time and using less space, compared with standard whole-plant pot tests in the glasshouse..

Marshall, R. ; Hanley, S. J. ; Hull, R. ; Moss, S. R.. 2013. The presence of two different target-site resistance mechanisms in individual plants of Alopecurus myosuroides Huds., identified using a quick molecular test for the characterisation of six ALS and seven ACCase SNPs. Pest Management Science 69 : 727 - 737.

BACKGROUND: Target-site resistance to ALS- and ACCase-inhibiting herbicides in the grass weed Alopecurus myosuroides is associated with well-characterised allelic variants encoding ALS- and ACCase-based resistance. The potential for combined ALS and ACCase resistance presents a threat to future control, given the extent to which these herbicides are used. The authors present a primer extension method for rapid detection of known resistance-conferring substitutions. RESULTS: Individuals showing combined resistance to field-rate mesosulfuron+iodosulfuron and cycloxydim were identified in four field-collected populations, with proportions ranging from 30 to 100%. Genotyping with the SNaPshot primer extension kit showed the T197 and L574 ALS and L1781 ACCase isoforms to be associated with ALS and ACCase resistance whenever they occurred. CONCLUSION: Combined ALS and ACCase target-site resistance threatens future control of A. myosuroides. The SNaPshot extension assay provides a reliable new multiplexable method for characterising known allelic variants of the ALS and ACCase genes of A. myosuroides. The method offers significant advantages over both CAPS/dCAPS and PASA in that full genotyping can be accomplished at any nucleotide position using a single extension primer..

Cummins, I. ; Wortley, D. J. ; Sabbadin, F. ; He ZheSi ; Coxon, C. R. ; Straker, H. E. ; Sellars, J. D. ; Knight, K. ; Edwards, L. ; Hughes, D. ; Kaundun, S. S. ; Hutchings, S. J. ; Steel, P. G. ; Edwards, R.. 2013. Key role for a glutathione transferase in multiple-herbicide resistance in grass weeds. Proceedings of the National Academy of Sciences of the United States of America 110 : 5812 - 5817.

Multiple-herbicide resistance (MHR) in black-grass (Alopecurus myosuroides) and annual rye-grass (Lolium rigidum) is a global problem leading to a loss of chemical weed control in cereal crops. Although poorly understood, in common with multiple-drug resistance (MDR) in tumors, MHR is associated with an enhanced ability to detoxify xenobiotics. In humans, MDR is linked to the overexpression of a pi class glutathione transferase (GSTP1), which has both detoxification and signaling functions in promoting drug resistance. In both annual rye-grass and black-grass, MHR was also associated with the increased expression of an evolutionarily distinct plant phi (F) GSTF1 that had a restricted ability to detoxify herbicides. When the black-grass A. myosuroides (Am) AmGSTF1 was expressed in Arabidopsis thaliana, the transgenic plants acquired resistance to multiple herbicides and showed similar changes in their secondary, xenobiotic, and antioxidant metabolism to those determined in MHR weeds. Transcriptome array experiments showed that these changes in biochemistry were not due to changes in gene expression. Rather, AmGSTF1 exerted a direct regulatory control on metabolism that led to an accumulation of protective flavonoids. Further evidence for a key role for this protein in MHR was obtained by showing that the GSTP1- and MDR-inhibiting pharmacophore 4-chloro-7-nitro-benzoxadiazole was also active toward AmGSTF1 and helped restore herbicide control in MHR black-grass. These studies demonstrate a central role for specific GSTFs in MHR in weeds that has parallels with similar roles for unrelated GSTs in MDR in humans and shows their potential as targets for chemical intervention in resistant weed management..

Délye, C. ; Menchari, Y. ; Michel, S. ; Cadet, É. ; Corre, V. le. 2013. A new insight into arable weed adaptive evolution: mutations endowing herbicide resistance also affect germination dynamics and seedling emergence. Annals of Botany 111 : 681 - 691.

Background and Aims: Selective pressures exerted by agriculture on populations of arable weeds foster the evolution of adaptive traits. Germination and emergence dynamics and herbicide resistance are key adaptive traits. Herbicide resistance alleles can have pleiotropic effects on a weed's life cycle. This study investigated the pleiotropic effects of three acetyl-coenzyme A carboxylase (ACCase) alleles endowing herbicide resistance on the seed-to-plant part of the life cycle of the grass weed Alopecurus myosuroides. Methods: In each of two series of experiments, A. myosuroides populations with homogenized genetic backgrounds and segregating for Leu1781, Asn2041 or Gly2078 ACCase mutations which arose independently were used to compare germination dynamics, survival in the soil and seedling pre-emergence growth among seeds containing wild-type, heterozygous and homozygous mutant ACCase embryos. Key Results: Asn2041 ACCase caused no significant effects. Gly2078 ACCase major effects were a co-dominant acceleration in seed germination (1.25- and 1.10-fold decrease in the time to reach 50% germination (T₅₀) for homozygous and heterozygous mutant embryos, respectively). Segregation distortion against homozygous mutant embryos or a co-dominant increase in fatal germination was observed in one series of experiments. Leu1781 ACCase major effects were a co-dominant delay in seed germination (1.41- and 1.22-fold increase in T₅₀ for homozygous and heterozygous mutant embryos, respectively) associated with a substantial co-dominant decrease in fatal germination. Conclusions: Under current agricultural systems, plants carrying Leu1781 or Gly2078 ACCase have a fitness advantage conferred by herbicide resistance that is enhanced or counterbalanced, respectively, by direct pleiotropic effects on the plant phenology. Pleiotropic effects associated with mutations endowing herbicide resistance undoubtedly play a significant role in the evolutionary dynamics of herbicide resistance in weed populations. Mutant ACCase alleles should also prove useful to investigate the role played by seed storage lipids in the control of seed dormancy and germination..

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