Spatial Distribution of Acetolactate Synthase Resistance Mechanisms in Neighboring Populations of Silky Windgrass (Apera spica-venti)

Silky windgrass is a serious weed in central and northern Europe. Its importance has escalated in recent years because of its growing resistance to acetolactate synthase (ALS)-inhibiting herbicides. This study investigated the resistance level for three herbicide sites of action in eight silky windgrass populations, collected in fields neighboring a field where iodosulfuron sodium salt–resistant silky windgrass had previously been found. Target site resistance (TSR) and non–target site resistance (NTSR) mechanisms were identified, and a spatial gradient distribution hypothesis of ALS resistance was tested. Populations showed large variations in ED50values to iodosulfuron, with resistance indices (RIs) ranging from 0.1 to 372. No cross-resistance was found to other herbicide groups with the same site of action as iodosulfuron. In contrast, resistance was observed to the acetyl-CoA carboxylase inhibitor, fenoxaprop ethyl ester (RI from 0.7 to 776), while the activity of prosulfocarb, an inhibitor of long-chain fatty-acid synthesis, was unaffected. Iodosulfuron-resistant phenotypes were associated with NTSR, while fenoxaprop ethyl ester resistance was caused by both NTSR and TSR (Ile-1781-Leu mutation). A large-scale trend in the spatial distribution of resistance to ALS indicated a decreasing resistance with increased distance from an epicenter. After finer-scale analysis, less than 0.05% of the residual variation could be attributed to spatial autocorrelation. The spatial resistance pattern was not correlated with the dominant wind direction, while there was a correlation between the resistant phenotype and type of crop. This study underlines that NTSR mechanisms do not always confer broad resistance to different herbicide subclasses and site of action, hence the complex relationship to resistant phenotype. NTSR mechanisms, in particular detoxification, were present at different levels for the herbicides tested in the silky windgrass populations of this study. The factors contributing to the spatial distribution of resistance remain elusive.

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Point Mutations as Main Resistance Mechanism Together With P450-Based Metabolism Confer Broad Resistance to Different ALS-Inhibiting Herbicides in Glebionis coronaria From Tunisia

Frontiers in Plant Science ◽

10.3389/fpls.2021.626702 ◽

2021 ◽

Vol 12 ◽

Author(s):

Zeineb Hada ◽

Yosra Menchari ◽

Antonia M. Rojano-Delgado ◽

Joel Torra ◽

Julio Menéndez ◽

...

Keyword(s):

Enzyme Activity ◽

Dose Response ◽

Resistance Mechanism ◽

Point Mutations ◽

Acetolactate Synthase ◽

Target Site ◽

Cross Resistance ◽

P450 Monooxygenase ◽

Target Site Resistance ◽

Sites Of Action

Resistance to acetolactate synthase (ALS) inhibiting herbicides has recently been reported in Glebionis coronaria from wheat fields in northern Tunisia, where the weed is widespread. However, potential resistance mechanisms conferring resistance in these populations are unknown. The aim of this research was to study target-site resistance (TSR) and non-target-site resistance (NTSR) mechanisms present in two putative resistant (R) populations. Dose–response experiments, ALS enzyme activity assays, ALS gene sequencing, absorption and translocation experiments with radiolabeled herbicides, and metabolism experiments were carried out for this purpose. Whole plant trials confirmed high resistance levels to tribenuron and cross-resistance to florasulam and imazamox. ALS enzyme activity further confirmed cross-resistance to these three herbicides and also to bispyribac, but not to flucarbazone. Sequence analysis revealed the presence of amino acid substitutions in positions 197, 376, and 574 of the target enzyme. Among the NTSR mechanisms investigated, absorption or translocation did not contribute to resistance, while evidences of the presence of enhanced metabolism were provided. A pretreatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion partially synergized with imazamox in post-emergence but not with tribenuron in dose–response experiments. Additionally, an imazamox hydroxyl metabolite was detected in both R populations in metabolism experiments, which disappeared with the pretreatment with malathion. This study confirms the evolution of cross-resistance to ALS inhibiting herbicides in G. coronaria from Tunisia through TSR and NTSR mechanisms. The presence of enhanced metabolism involving P450 is threatening the chemical management of this weed in Tunisian wheat fields, since it might confer cross-resistance to other sites of action.

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Target-Site and Non-target-Site Resistance Mechanisms Confer Multiple and Cross- Resistance to ALS and ACCase Inhibiting Herbicides in Lolium rigidum From Spain

Frontiers in Plant Science ◽

10.3389/fpls.2021.625138 ◽

2021 ◽

Vol 12 ◽

Author(s):

Joel Torra ◽

José María Montull ◽

Andreu Taberner ◽

Nawaporn Onkokesung ◽

Neil Boonham ◽

...

Keyword(s):

Glutathione Transferase ◽

Point Mutations ◽

Acetolactate Synthase ◽

Target Site ◽

Cross Resistance ◽

Lolium Rigidum ◽

P450 Monooxygenase ◽

Winter Cereals ◽

Target Site Resistance ◽

Sites Of Action

Lolium rigidum is one the worst herbicide resistant (HR) weeds worldwide due to its proneness to evolve multiple and cross resistance to several sites of action (SoA). In winter cereals crops in Spain, resistance to acetolactate synthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides has become widespread, with farmers having to rely on pre-emergence herbicides over the last two decades to maintain weed control. Recently, lack of control with very long-chain fatty acid synthesis (VLCFAS)-inhibiting herbicides has been reported in HR populations that are difficult to manage by chemical means. In this study, three Spanish populations of L. rigidum from winter cereals were confirmed as being resistant to ALS- and ACCase-inhibiting herbicides, with broad-ranging resistance toward the different chemistries tested. In addition, reduced sensitivity to photosystem II-, VLCFAS-, and phytoene desaturase-inhibiting herbicides were confirmed across the three populations. Resistance to ACCase-inhibiting herbicides was associated with point mutations in positions Trp-2027 and Asp-2078 of the enzyme conferring target site resistance (TSR), while none were detected in the ALS enzyme. Additionally, HR populations contained enhanced amounts of an ortholog of the glutathione transferase phi (F) class 1 (GSTF1) protein, a functional biomarker of non-target-site resistance (NTSR), as confirmed by enzyme-linked immunosorbent assays. Further evidence of NTSR was obtained in dose-response experiments with prosulfocarb applied post-emergence, following pre-treatment with the cytochrome P450 monooxygenase inhibitor malathion, which partially reversed resistance. This study confirms the evolution of multiple and cross resistance to ALS- and ACCase inhibiting herbicides in L. rigidum from Spain by mechanisms consistent with the presence of both TSR and NTSR. Moreover, the results suggest that NTSR, probably by means of enhanced metabolism involving more than one detoxifying enzyme family, confers cross resistance to other SoA. The study further demonstrates the urgent need to monitor and prevent the further evolution of herbicide resistance in L. rigidum in Mediterranean areas.

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Evolution of target and non-target based multiple herbicide resistance in a single Palmer amaranth (Amaranthus palmeri) population from Kansas

Weed Technology ◽

10.1017/wet.2020.32 ◽

2020 ◽

Vol 34 (3) ◽

pp. 447-453

Author(s):

Sushila Chaudhari ◽

Vijay K. Varanasi ◽

Sridevi Nakka ◽

Prasanta C. Bhowmik ◽

Curtis R. Thompson ◽

...

Keyword(s):

Resistance Mechanism ◽

Acetolactate Synthase ◽

Palmer Amaranth ◽

Target Site ◽

Epsp Synthase ◽

High Incidence ◽

Evolution Of Resistance ◽

Target Site Resistance ◽

Herbicide Atrazine ◽

Sites Of Action

AbstractThe evolution of resistance to multiple herbicides in Palmer amaranth is a major challenge for its management. In this study, a Palmer amaranth population from Hutchinson, Kansas (HMR), was characterized for resistance to inhibitors of photosystem II (PSII) (e.g., atrazine), acetolactate synthase (ALS) (e.g., chlorsulfuron), and EPSP synthase (EPSPS) (e.g., glyphosate), and this resistance was investigated. About 100 HMR plants were treated with field-recommended doses (1×) of atrazine, chlorsulfuron, and glyphosate, separately along with Hutchinson multiple-herbicide (atrazine, chlorsulfuron, and glyphosate)–susceptible (HMS) Palmer amaranth as control. The mechanism of resistance to these herbicides was investigated by sequencing or amplifying the psbA, ALS, and EPSPS genes, the molecular targets of atrazine, chlorsulfuron, and glyphosate, respectively. Fifty-two percent of plants survived a 1× (2,240 g ai ha−1) atrazine application with no known psbA gene mutation, indicating the predominance of a non–target site resistance mechanism to this herbicide. Forty-two percent of plants survived a 1× (18 g ai ha−1) dose of chlorsulfuron with proline197serine, proline197threonine, proline197alanine, and proline197asparagine, or tryptophan574leucine mutations in the ALS gene. About 40% of the plants survived a 1× (840 g ae ha−1) dose of glyphosate with no known mutations in the EPSPS gene. Quantitative PCR results revealed increased EPSPS copy number (50 to 140) as the mechanism of glyphosate resistance in the survivors. The most important finding of this study was the evolution of resistance to at least two sites of action (SOAs) (~50% of plants) and to all three herbicides due to target site as well as non–target site mechanisms. The high incidence of individual plants with resistance to multiple SOAs poses a challenge for effective management of this weed.

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Cross Resistance to Diquat in Glyphosate/Paraquat-Resistant Conyza bonariensis and Conyza canadensis and Confirmation of 2,4-D Resistance in Conyza bonariensis

Weed Technology ◽

10.1017/wet.2021.11 ◽

2021 ◽

pp. 1-22

Author(s):

Marcelo L. Moretti ◽

Lucas K. Bobadilla ◽

Bradley D. Hanson

Keyword(s):

Management Strategies ◽

Resistance Management ◽

Cross Resistance ◽

Similar Response ◽

Weed Species ◽

Conyza Bonariensis ◽

Whole Plant ◽

Site Of Action ◽

Target Site Resistance ◽

Sites Of Action

Abstract Hairy fleabane and horseweed are pervasive weed species in agriculture. Glyphosate-resistant (GR) and glyphosate-paraquat-resistant (GPR) biotypes challenge current management strategies. These GR and GPR biotypes have non-target-site-resistance (NTSR), which can confer resistance to herbicides with different sites of action. This study’s objective was to characterize the response of GR, GPR, and glyphosate-paraquat-susceptible (GPS) biotypes of both Conyza spp. to herbicides with a different site of action. Whole-plant dose-response bioassays indicated a similar response among tested biotypes of both Conyza spp. to rimsulfuron, dicamba, hexazinone, glufosinate, flumioxazin, saflufenacil, or mesotrione. The C. bonariensis GR and GPR biotypes were 2.7- and 2.9-fold resistant to 2,4-D relative to the GPS biotype (GR50 766.7 g ai ha-1), confirming 2,4-D resistance in C. bonariensis for the first time in California. The GR and GPR biotypes were not cross-resistant to dicamba. No differences in response to 2,4-D were observed among C. canadensis biotypes with a GR50 ranging from 150.2 to 277.4 g ai ha-1. The GPR biotypes of both species were cross-resistant to diquat with a 44.0-fold resistance in C. bonariensis (GR50 863.7 g ai ha-1) and 15.6-fold resistance in C. canadensis (GR50 563.1 g ai ha-1). The confirmation of multiple resistances to glyphosate, paraquat, and 2,4-D in C. bonariensis curtails herbicide site of action alternatives and jeopardizes resistance management strategies based on herbicide rotation and tank-mixtures, underscoring the critical need for non-chemical weed control alternatives.

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Target-Site Resistance Mechanisms to Tribenuron-methyl and Cross-resistance Patterns to ALS-inhibiting Herbicides of Catchweed Bedstraw (Galium aparine) with Different ALS Mutations

Weed Science ◽

10.1017/wsc.2018.70 ◽

2018 ◽

Vol 67 (2) ◽

pp. 183-188 ◽

Cited By ~ 2

Author(s):

Wei Deng ◽

Yingjie Di ◽

Jingxuan Cai ◽

Yueyang Chen ◽

Shuzhong Yuan

Keyword(s):

Acetolactate Synthase ◽

Resistance Mechanisms ◽

Target Site ◽

Cross Resistance ◽

Susceptible Population ◽

Resistance Evolution ◽

Galium Aparine ◽

Resistance Patterns ◽

Target Site Resistance ◽

Tribenuron Methyl

AbstractCatchweed bedstraw (Galium aparine L.) is a problematic dicot weed that occurs in major winter wheat (Triticum aestivum L.) fields in China. Tribenuron-methyl has been widely used to control broadleaf weeds since 1988 in China. However, overuse has led to the resistance evolution of G. aparine to tribenuron-methyl. In this study, 20 G. aparine populations collected from Shandong and Henan provinces were used to determine tribenuron-methyl resistance and target-site resistance mechanisms. In dose–response experiments, 12 G. aparine populations showed different resistance levels (2.92 to 842.41-fold) to tribenuron-methyl compared with the susceptible population. Five different acetolactate synthase (ALS) mutations (Pro-197-Leu, Pro-197-Ser, Pro-197-His, Asp-376-Glu, and Trp-574-Leu) were detected in different resistant populations. Individuals heterozygous for Pro-197-Ser and Trp-574-Leu mutations were also observed in a resistant population (HN6). In addition, pHB4 (Pro-197-Ser), pHB7 (Pro-197-His), pHB8 (Pro-197-Leu), pHB5 (Asp-376-Glu), and pHB3 (Trp-574-Leu) subpopulations individually homozygous for specific ALS mutations were generated to evaluate the cross-resistance to ALS-inhibiting herbicides. The pHB4, pHB7, pHB8, pHB5, and pHB3 subpopulations all were resistant to sulfonylurea, pyrazosulfuron-ethyl, triazolopyrimidine, flumetsulam, sulfonylamino-carbonyl-triazolinone, flucarbazone-sodium, pyrimidinyl thiobenzoate, pyribenzoxim, and the imidazolinone imazethapyr. These results indicated the diversity of the resistance-conferring ALS mutations in G. aparine, and all these mutations resulted in broad cross-resistance to five kinds of ALS-inhibiting herbicides.

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Controlling Herbicide-Resistant Annual Bluegrass (Poa annua) Phenotypes with Methiozolin

Weed Technology ◽

10.1017/wet.2017.13 ◽

2017 ◽

Vol 31 (3) ◽

pp. 470-476 ◽

Cited By ~ 3

Author(s):

James T. Brosnan ◽

Jose J. Vargas ◽

Gregory K. Breeden ◽

Sarah L. Boggess ◽

Margaret A. Staton ◽

...

Keyword(s):

Acetolactate Synthase ◽

Target Site ◽

Multiple Resistance ◽

Herbicide Resistant ◽

Annual Bluegrass ◽

Microtubule Inhibitors ◽

Effective Option ◽

Target Site Resistance ◽

Susceptible Control ◽

Als Inhibitors

Methiozolin is an isoxazoline herbicide being investigated for selective POST annual bluegrass control in managed turfgrass. Research was conducted to evaluate methiozolin efficacy for controlling two annual bluegrass phenotypes with target-site resistance to photosystem II (PSII) or enolpyruvylshikimate-3-phosphate synthase (EPSPS)-inhibiting herbicides (i.e., glyphosate), as well as phenotypes with multiple resistance to microtubule and EPSPS or PSII and acetolactate synthase (ALS)-inhibiting herbicides. All resistant phenotypes were established in glasshouse culture along with a known herbicide-susceptible control and treated with methiozolin at 0, 125, 250, 500, 1000, 2000, 4000, or 8000 g ai ha−1. Methiozolin effectively controlled annual bluegrass with target-site resistance to inhibitors of EPSPS, PSII, as well as multiple resistance to EPSPS and microtubule inhibitors. Methiozolin rates required to reduce aboveground biomass of these resistant phenotypes 50% (GR50 values) were not significantly different from the susceptible control, ranging from 159 to 421 g ha−1. A phenotype with target-site resistance to PSII and ALS inhibitors was less sensitive to methiozolin (GR50=862 g ha−1) than a susceptible phenotype (GR50=423 g ha−1). Our findings indicate that methiozolin is an effective option for controlling select annual bluegrass phenotypes with target-site resistance to several herbicides.

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Target site–based penoxsulam resistance in barnyardgrass (Echinochloa crus-galli) from China

Weed Science ◽

10.1017/wsc.2019.5 ◽

2019 ◽

Vol 67 (3) ◽

pp. 281-287 ◽

Cited By ~ 1

Author(s):

Jiapeng Fang ◽

Tingting Liu ◽

Yuhua Zhang ◽

Jun Li ◽

Liyao Dong

Keyword(s):

Amino Acid ◽

Amino Acid Sequence ◽

Acetolactate Synthase ◽

Target Site ◽

Cross Resistance ◽

Predicted Amino Acid Sequence ◽

Sequence Analyses ◽

Als Inhibitors ◽

Higher Sensitivity

AbstractBarnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is acknowledged to be the most troublesome weed in rice fields in Anhui and Jiangsu provinces of China. It cannot be effectively controlled using certain acetolactate synthase (ALS)-inhibiting herbicides, including penoxsulam. Echinochloa crus-galli samples with suspected resistance to penoxsulam were collected to identify the target site–based mechanism underlying this resistance. Populations AXXZ-2 and JNRG-2 showed 33- and 7.3-fold resistance to penoxsulam, respectively, compared with the susceptible JLGY-3 population. Cross-resistance to other ALS inhibitors was reported in AXXZ-2 but not in JNRG-2, and occasionally showed higher sensitivity than JLGY-3. In vitro ALS activity assays revealed that penoxsulam concentrations required to inhibit 50% of ALS activity were 11 and 5.2 times greater in AXXZ-2 and JNRG-2, respectively, than in JLGY-3. DNA and predicted amino acid sequence analyses of ALS revealed Ala-205-Val and Ala-122-Gly substitutions in AXXZ-2 and JNRG-2, respectively. Our results indicate that these substitutions in ALS are at least partially responsible for resistance to penoxsulam.

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Negative Cross-Resistance of Acetolactate Synthase Inhibitor–Resistant Kochia (Kochia scoparia) to Protoporphyrinogen Oxidase– and Hydroxyphenylpyruvate Dioxygenase–Inhibiting Herbicides

Weed Technology ◽

10.1614/wt-d-12-00020.1 ◽

2012 ◽

Vol 26 (3) ◽

pp. 570-574 ◽

Cited By ~ 3

Author(s):

Hugh J. Beckie ◽

Eric N. Johnson ◽

Anne Légère

Keyword(s):

Growth And Development ◽

Null Hypothesis ◽

Acetolactate Synthase ◽

Pleiotropic Effect ◽

Cross Resistance ◽

Kochia Scoparia ◽

Protoporphyrinogen Oxidase ◽

Synthase Inhibitor ◽

Sites Of Action ◽

Als Inhibitor

This greenhouse experiment examined the response of homozygous susceptible and acetolactate synthase (ALS) inhibitor–resistant plants from six Canadian kochia accessions with the Pro197 or Trp574 mutation to six alternative herbicides of different sites of action. The null hypothesis was ALS-inhibitor–resistant and –susceptible plants from within and across accessions would respond similarly to herbicides of different sites of action. This hypothesis was accepted for all accessions except that of MBK2 with the Trp574 mutation. Resistant plants of that accession were 80, 60, and 50% more sensitive than susceptible plants to pyrasulfotole, mesotrione (hydroxyphenylpyruvate dioxygenase [HPPD] inhibitors), and carfentrazone (protoporphyrinogen oxidase [PPO] inhibitor), respectively. However, no differential dose response between resistant and susceptible plants of this kochia accession to bromoxynil, fluroxypyr, or glyphosate was observed. A previous study had found marked differences in growth and development between resistant and susceptible plants of this accession, but not of the other accessions examined in this experiment. Negative cross-resistance exhibited by resistant plants of accession MBK2 to PPO and HPPD inhibitors in this experiment may be a pleiotropic effect related to the Trp574 mutation.

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Non-target-Site Resistance in Lolium spp. Globally: A Review

Frontiers in Plant Science ◽

10.3389/fpls.2020.609209 ◽

2021 ◽

Vol 11 ◽

Author(s):

Andréia K. Suzukawa ◽

Lucas K. Bobadilla ◽

Carol Mallory-Smith ◽

Caio A. C. G. Brunharo

Keyword(s):

Main Tool ◽

Mechanisms Of Action ◽

Target Site ◽

Microtubule Assembly ◽

Acetohydroxyacid Synthase ◽

Cross Resistance ◽

Long Chain Fatty Acids ◽

Single Population ◽

Target Site Resistance ◽

Agricultural Areas

The Lolium genus encompasses many species that colonize a variety of disturbed and non-disturbed environments. Lolium perenne L. spp. perenne, L. perenne L. spp. multiflorum, and L. rigidum are of particular interest to weed scientists because of their ability to thrive in agricultural and non-agricultural areas. Herbicides are the main tool to control these weeds; however, Lolium spp. populations have evolved multiple- and cross-resistance to at least 14 herbicide mechanisms of action in more than 21 countries, with reports of multiple herbicide resistance to at least seven mechanisms of action in a single population. In this review, we summarize what is currently known about non-target-site resistance in Lolium spp. to acetyl CoA carboxylase, acetohydroxyacid synthase, microtubule assembly, photosystem II, 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthetase, very-long chain fatty acids, and photosystem I inhibitors. We suggest research topics that need to be addressed, as well as strategies to further our knowledge and uncover the mechanisms of non-target-site resistance in Lolium spp.

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Herbicide diagnostics reveal multiple patterns of synthetic auxin resistance in kochia (Bassia scoparia)

Weed Technology ◽

10.1017/wet.2021.69 ◽

2021 ◽

pp. 1-28

Author(s):

Charles M. Geddes ◽

Mallory L. Owen ◽

Teandra E. Ostendorf ◽

Julia Y. Leeson ◽

Shaun M. Sharpe ◽

...

Keyword(s):

Great Plains ◽

Dose Response ◽

Weed Management ◽

Acetolactate Synthase ◽

The United States ◽

Cross Resistance ◽

Visible Injury ◽

Synthetic Auxin ◽

Auxin Resistance ◽

Sites Of Action

Abstract Herbicide-resistant (HR) kochia is a growing problem in the Great Plains region of Canada and the United States (U.S.). Resistance to up to four herbicide sites of action, including photosystem II inhibitors, acetolactate synthase inhibitors, synthetic auxins, and the 5-enolpyruvylshikimate-3-phosphate synthase inhibitor glyphosate have been reported in many areas of this region. Despite being present in the U.S. since 1993/1994, auxinic-HR kochia is a recent and growing phenomenon in Canada. This study was designed to characterize (a) the level of resistance and (b) patterns of cross-resistance to dicamba and fluroxypyr in 12 putative auxinic-HR kochia populations from western Canada. The incidence of dicamba-resistant individuals ranged among populations from 0% to 85%, while fluroxypyr-resistant individuals ranged from 0% to 45%. In whole-plant dose-response bioassays, the populations exhibited up to 6.5-fold resistance to dicamba and up to 51.5-fold resistance to fluroxypyr based on visible injury 28 days after application. Based on plant survival estimates, the populations exhibited up to 3.7-fold resistance to dicamba and up to 72.5-fold resistance to fluroxypyr. Multiple patterns of synthetic auxin resistance were observed, where one population from Cypress County, Alberta was resistant to dicamba but not fluroxypyr, while another from Rocky View County, Alberta was resistant to fluroxypyr but not dicamba based on single-dose population screening and dose-response bioassays. These results suggest that multiple mechanisms may confer resistance to dicamba and/or fluroxypyr in Canadian kochia populations. Further research is warranted to determine these mechanisms. Farmers are urged to adopt proactive non-chemical weed management tools in an effort to preserve efficacy of the remaining herbicide options available for control of HR kochia.

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