Acetolactate Synthase Inhibitor–Resistant False Cleavers (Galium spurium) in Western Canada

Cleavers species (false cleavers and catchweed bedstraw) are among the top 10 most abundant weeds across the prairie region of western Canada, and are increasing in relative abundance at the fastest rate since the 1970s. In 2008, two false cleavers populations from Tisdale and Choiceland, Saskatchewan, were suspected of acetolactate synthase (ALS) –inhibitor resistance. Dose-response experiments were conducted with the use of imazethapyr and florasulam, both ALS inhibitors, as well as fluroxypyr, a synthetic auxin. Additionally, a 1,954–base-pair region of theALSgene including sites known to conferALSresistance were sequenced. Both populations were highly resistant to imazethapyr (resistance factors greater than 100), one population (Tisdale) was highly resistant to florasulam (Choiceland population susceptible, although a second, larger screening of 200 individuals indicated low frequency [2%] florasulam resistance), and both populations were susceptible to fluroxypyr. All sequenced Tisdale individuals screened with imazethapyr posessed the Trp574Leu mutation. In contrast, three point mutations were found for Choiceland individuals sequenced: Ser653Asn, Trp574Leu, and Asp376Glu. TheseALStarget-site mutations have not been documented previously in this species.

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In vitro and whole-plant magnitude and cross-resistance characterization of two imidazolinone-resistant sugarbeet (Beta vulgaris) somatic cell selections

Weed Science ◽

10.1017/s0043174500090123 ◽

1998 ◽

Vol 46 (1) ◽

pp. 24-29 ◽

Cited By ~ 8

Author(s):

Terry R. Wright ◽

Donald Penner

Keyword(s):

Somatic Cell ◽

Shoot Culture ◽

Acetolactate Synthase ◽

Cross Resistance ◽

Shoot Cultures ◽

Als Inhibitors ◽

Whole Plants ◽

Inhibitor Resistance ◽

Als Inhibitor

Acetolactate synthase (ALS)-inhibiting herbicide carryover in soil can severely affect sugarbeets grown in the year(s) following application. Two newly developed imidazolinone-resistant (IMI-R) sugarbeet somatic cell selections (Sir-13 and 93R30B) were examined for magnitude of resistance and extent of cross-resistance to other classes of ALS inhibitors and compared to a previously developed sulfonylurea-resistant (SU-R) selection, Sur. In vitro shoot culture tests indicated Sir-13 resistance was specific to imidazolinone (IMI) herbicides at approximately a 100-fold resistance compared to the sensitive control sugarbeet. Sur was 10,000-fold resistant to the sulfonylurea (SU) herbicide, chlorsulfuron, and 40-fold resistant to the triazolopyrimidine sulfonanilide (TP) herbicide, flumetsulam, but not cross-resistant to the IMI herbicides. 93R30B was selected for IMI-R from a plant homozygous for the SU-R allele,Sur, and displayed similar in vitro SU-R and TP-R as Sur, but also displayed a very high resistance to various IMI herbicides (400- to 3,600-fold). Compared to the sensitive control, Sir-13 was 300- and > 250-fold more resistant to imazethapyr and imazamox residues in soil, respectively. Response by whole plants to postemergence herbicide applications was similar to that observed in shoot cultures. Sir-13 exhibited > 100-fold resistance to imazethapyr as well as imazamox, and 93R30B showed > 250-fold resistance to both herbicides. 93R30B showed great enough resistance to imazamox to merit consideration of imazamox for use as a herbicide in these sugarbeets. Sir-13 showed a two- to threefold higher level of resistance in the homozygous vs. heterozygous state, indicating that like most ALS-inhibitor resistance traits, it was semidominantly inherited.

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Glyphosate- and Acetolactate Synthase Inhibitor–Resistant Kochia (Kochia scoparia) in Western Canada

Weed Science ◽

10.1614/ws-d-12-00140.1 ◽

2013 ◽

Vol 61 (2) ◽

pp. 310-318 ◽

Cited By ~ 50

Author(s):

Hugh J. Beckie ◽

Robert E. Blackshaw ◽

Ryan Low ◽

Linda M. Hall ◽

Connie A. Sauder ◽

...

Keyword(s):

Dose Response ◽

Best Management Practices ◽

Management Practices ◽

Acetolactate Synthase ◽

Glyphosate Resistance ◽

Western Canada ◽

Wild Oat ◽

Green Foxtail ◽

Inhibitor Resistance ◽

Als Inhibitor

In summer, 2011, we investigated suspected glyphosate-resistant (GR) kochia in three chem-fallow fields (designated F1, F2, F3, each farmed by a different grower) in southern Alberta. This study characterizes glyphosate resistance in those populations, based on data from dose–response experiments. In a greenhouse experiment, the three populations exhibited a resistance factor ranging from 4 to 6 based on shoot biomass response (GR50ratios), or 5 to 7 based on survival response (LD50ratios). Similar results were found in a field dose–response experiment at Lethbridge, AB, in spring 2012 using the F2 kochia population. In fall 2011, we surveyed 46 fields within a 20-km radius of the three chem-fallow fields for GR kochia. In the greenhouse, populations were screened with glyphosate at 900 g ae ha−1. Seven populations were confirmed as GR, the farthest site located about 13 km from the three originally confirmed populations. An additional GR population more than 100 km away was later confirmed. Populations were screened for acetolactate synthase (ALS)–inhibitor (thifensulfuron : tribenuron) and dicamba resistance in the greenhouse, with molecular characterization of ALS-inhibitor resistance in the F1, F2, and F3 populations. All GR populations were resistant to the ALS-inhibiting herbicide, but susceptible to dicamba. ALS-inhibitor resistance in kochia was conferred by Pro197, Asp376, or Trp574amino acid substitutions. Based upon a simple empirical model with a parameter for selection pressure, calculated from weed relative abundance and glyphosate efficacy, and a parameter for seedbank longevity, kochia, wild oat, and green foxtail were the top three weeds, respectively, predicted at risk of selection for glyphosate resistance in the semiarid Grassland region of the Canadian prairies; wild oat, green foxtail, and cleavers species were predicted at greatest risk in the subhumid Parkland region. This study confirms the first occurrence of a GR weed in western Canada. Future research on GR kochia will include monitoring, biology and ecology, fitness, mechanism of resistance, and best management practices.

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ALS–Resistant Annual Sedge (Cyperus compressus) Confirmed in Turfgrass

Weed Science ◽

10.1614/ws-d-15-00094.1 ◽

2016 ◽

Vol 64 (1) ◽

pp. 33-41 ◽

Cited By ~ 9

Author(s):

Patrick E. McCullough ◽

Jialin Yu ◽

J. Scott McElroy ◽

S. Chen ◽

H. Zhang ◽

...

Keyword(s):

Laboratory Experiments ◽

Acetolactate Synthase ◽

Shoot Biomass ◽

Resistance Level ◽

Physiological Basis ◽

History Of ◽

Leaf Tissues ◽

Als Inhibitors ◽

Inhibitor Resistance ◽

Als Inhibitor

Acetolactate synthase (ALS) inhibitors are widely used for POST control of sedges in turfgrass. A suspected resistant (R) biotype of annual sedge was collected from a bermudagrass turf in Georgia with a history of exclusive use of halosulfuron. Research was conducted to evaluate the resistance level of this biotype to halosulfuron, efficacy of ALS-inhibiting herbicides and other mechanisms of action for control, and the molecular and physiological basis for resistance. In greenhouse experiments, the halosulfuron rate required to reduce shoot biomass 50% in comparison with the nontreated at 8 wk after treatment (WAT) were 8 and > 1,120 g ai ha−1for the S (susceptible) and R biotypes, respectively. Imazapic, sulfosulfuron, and trifloxysulfuron reduced biomass of the S biotype greater than 60% at 8 WAT, but biomass was reduced less than 20% for the R biotype. Glufosinate, glyphosate, MSMA, and sulfentrazone reduced shoot biomass of the R biotype by 93, 86, 97, and 45%, respectively. In laboratory experiments, the halosulfuron concentration required to inhibit ALS activity by 50% in excised leaf tissues was 5.8 and > 1,000 μM for the S and R biotypes, respectively. Gene sequencing of the R biotype revealed a Pro-197-Ser substitution that confers resistance to ALS inhibitors. This is the first report of ALS-inhibitor resistance in annual sedge and herbicide resistance in a sedge species from a turfgrass system.

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Multiple herbicide resistance in California Italian ryegrass (Lolium perenne ssp. multiflorum): characterization of ALS-inhibiting herbicide resistance

Weed Science ◽

10.1017/wsc.2019.1 ◽

2019 ◽

Vol 67 (3) ◽

pp. 273-280 ◽

Cited By ~ 4

Author(s):

Parsa Tehranchian ◽

Vijay K. Nandula ◽

Maor Matzrafi ◽

Marie Jasieniuk

Keyword(s):

Lolium Perenne ◽

Herbicide Resistance ◽

Resistance Mechanism ◽

Acetolactate Synthase ◽

Target Site ◽

Italian Ryegrass ◽

Resistance Level ◽

Als Inhibitors ◽

Inhibitor Resistance ◽

Als Inhibitor

AbstractMultiple resistance to glyphosate, sethoxydim, and paraquat was previously confirmed in two Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] populations, MR1 and MR2, in northern California. Preliminary greenhouse studies revealed that both populations were also resistant to imazamox and mesosulfuron, both of which are acetolactate synthase (ALS)-inhibiting herbicides. In this study, three subpopulations, MR1-A (from seed of MR1 plants that survived a 16X rate of sethoxydim), MR1-P (from seed of MR1 plants that survived a 2X rate of paraquat), and MR2 (from seed of MR2 plants that survived a 16X rate of sethoxydim), were investigated to determine the resistance level to imazamox and mesosulfuron, evaluate other herbicide options for the control of these multiple resistant L. perenne ssp. multiflorum, and characterize the underlying ALS-inhibitor resistance mechanism(s). Based on LD50 values, the MR1-A, MR1-P, and MR2 subpopulations were 38-, 29-, 8-fold and 36-, 64-, and 3-fold less sensitive to imazamox and mesosulfuron, respectively, relative to the susceptible (Sus) population. Only MR1-P and MR2 plants were cross-resistant to rimsulfuron, whereas both MR1 subpopulations were cross-resistant to imazethapyr. Pinoxaden (ACCase inhibitor [phenylpyrazoline 'DEN']) only controlled MR2 and Sus plants at the labeled field rate. However, all plants were effectively controlled (>99%) with the labeled field rate of glufosinate. Based on I50 values, MR1-A, MR-P, and MR2 plants were 712-, 1,104-, and 3-fold and 10-, 18-, and 5-fold less responsive to mesosulfuron and imazamox, respectively, than the Sus plants. Sequence alignment of the ALS gene of resistant plants revealed a missense single-nucleotide polymorphism resulting in a Trp-574-Leu substitution in MR1-A and MR1-P plants, heterozygous in both, but not in the MR2 plants. An additional homozygous substitution, Asp-376-Glu, was identified in the MR1-A plants. Addition of malathion or piperonyl butoxide did not alter the efficacy of mesosulfuron on MR2 plants. In addition, the presence of 2,4-D had no effect on the response of mesosulfuron on the MR2 and Sus. These results suggest an altered target site is the mechanism of resistance to ALS inhibitors in MR1-A and MR1-P plants, whereas a non–target site based resistance apparatus is present in the MR2 plants.

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Nontarget-Site Resistance to ALS Inhibitors in Waterhemp (Amaranthus tuberculatus)

Weed Science ◽

10.1614/ws-d-14-00139.1 ◽

2015 ◽

Vol 63 (2) ◽

pp. 399-407 ◽

Cited By ~ 31

Author(s):

Jiaqi Guo ◽

Chance W. Riggins ◽

Nicholas E. Hausman ◽

Aaron G. Hager ◽

Dean E. Riechers ◽

...

Keyword(s):

Acetolactate Synthase ◽

Enzyme Assays ◽

Whole Plant ◽

Site Of Action ◽

Amaranthus Tuberculatus ◽

Resistance Trait ◽

Als Inhibitors ◽

Moderate Resistance ◽

Inhibitor Resistance ◽

Als Inhibitor

A waterhemp population (MCR) previously characterized as resistant to 4-hydroxyphenylpyruvate dioxygenase and photosystem II inhibitors demonstrated both moderate and high levels of resistance to acetolactate synthase (ALS) inhibitors. Plants from the MCR population exhibiting high resistance to ALS inhibitors contained the commonly found Trp574Leu ALS amino acid substitution, whereas plants with only moderate resistance did not have this substitution. A subpopulation (JG11) was derived from the MCR population in which the moderate-resistance trait was isolated from the Trp574Leu mutation. Results from DNA sequencing and ALS enzyme assays demonstrated that resistance to ALS inhibitors in the JG11 population was not due to an altered site of action. This nontarget-site ALS-inhibitor resistance was characterized with whole-plant dose–response experiments using herbicides from each of the five commercialized families of ALS-inhibiting herbicides. Resistance ratios ranging from 3 to 90 were obtained from the seven herbicides evaluated. Nontarget-site resistance to ALS has been rarely documented in eudicot weeds, and adds to the growing list of resistance traits evolved in waterhemp.

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Transfer and Expression of ALS Inhibitor Resistance from Palmer Amaranth (Amaranthus palmeri) to anA. spinosus×A. palmeriHybrid

Weed Science ◽

10.1614/ws-d-15-00172.1 ◽

2016 ◽

Vol 64 (2) ◽

pp. 240-247 ◽

Cited By ~ 17

Author(s):

William T. Molin ◽

Vijay K. Nandula ◽

Alice A. Wright ◽

Jason A. Bond

Keyword(s):

Field Experiments ◽

Acetolactate Synthase ◽

Palmer Amaranth ◽

Enzyme Assays ◽

Amaranthus Palmeri ◽

Weed Species ◽

Als Inhibitors ◽

Inhibitor Resistance ◽

Als Inhibitor ◽

Interspecific Transfer

Transfer of herbicide resistance among closely related weed species is a topic of growing concern. A spiny amaranth × Palmer amaranth hybrid was confirmed resistant to several acetolactate synthase (ALS) inhibitors including imazethapyr, nicosulfuron, pyrithiobac, and trifloxysulfuron. Enzyme assays indicated that the ALS enzyme was insensitive to pyrithiobac and sequencing revealed the presence of a known resistance conferring point mutation, Trp574Leu. Alignment of the ALS gene for Palmer amaranth, spiny amaranth, and putative hybrids revealed the presence of Palmer amaranth ALS sequence in the hybrids rather than spiny amaranth ALS sequences. In addition, sequence upstream of the ALS in the hybrids matched Palmer amaranth and not spiny amaranth. The potential for transfer of ALS inhibitor resistance by hybridization has been demonstrated in the greenhouse and in field experiments. This is the first report of gene transfer for ALS inhibitor resistance documented to occur in the field without artificial/human intervention. These results highlight the need to control related species in both field and surrounding noncrop areas to avoid interspecific transfer of resistance genes.

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Resistance in Canadian biotypes of wild mustard (Sinapis arvensis) to acetolactate synthase inhibiting herbicides

Weed Science ◽

10.1614/ws-05-003r1.1 ◽

2005 ◽

Vol 53 (5) ◽

pp. 631-639 ◽

Cited By ~ 28

Author(s):

Suzanne I. Warwick ◽

Connie Sauder ◽

Hugh J. Beckie

Keyword(s):

Amino Acid ◽

Single Gene ◽

Acetolactate Synthase ◽

Western Canada ◽

Nucleotide Polymorphisms ◽

Weed Species ◽

Susceptible Population ◽

Wild Mustard ◽

Als Inhibitors ◽

Als Inhibitor

Multiple cases of ALS inhibitor-resistant weed biotypes are reported for many species, including wild mustard. The physiological extent and molecular basis of resistance to ALS inhibitors was compared in four biotypes of wild mustard from western Canada: a sulfonylurea (SU)-resistant (R) biotype from Manitoba detected in 1992; an SU (ethametsulfuron)-R biotype from Alberta detected in 1993 (metabolism-based resistance); an SU-R biotype from Manitoba detected in 2002; and a SU- and imidazolinone (IMI)-R biotype from Saskatchewan detected in 2002. Herbicide dose-response experiments confirmed that the two Manitoba biotypes were resistant to the SU herbicides ethametsulfuron and tribenuron : thifensulfuron mixture, whereas the Saskatchewan biotype was resistant to both SU herbicides and to imazethapyr, an IMI herbicide. Sequence analysis of theALSgene detected target site mutations in three of the four R biotypes, with amino acid substitutions Pro197(CCT) to Ser (TCT) [Domain A of the gene] in the two SU-R Manitoba biotypes and Trp574(TGG) to Leu (TTG) [Domain B] in the Saskatchewan biotype. The Alberta SU-R biotype had the sameALSnucleotide and amino acid sequence as the susceptible population at these two positions. Two heterozygous individuals [Trp574(Tt/gG)] were detected in the Saskatchewan biotype, and genetic segregation for nucleotide bases and resistance phenotype was consistent with single gene control. Nucleotide variation in neutral regions of theALSgene varied with biotype, with no variation in the two Manitoba biotypes, two variants in the Saskatchewan biotype, and 16 neutral nucleotide polymorphisms (0.9%) in the Alberta biotype. The occurrence of at least three different ALS inhibitor-R biotypes in this important weed species is likely to impact negatively on the use of ALS inhibitors, such as the IMIs, and serves as a warning for strict implementation of herbicide rotations to prevent or delay the evolution and spread of such populations.

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Characterization of Acetolactate Synthase (ALS)-Inhibitor Resistance in Pennsylvania smartweed (Persicaria pensylvanica)

Weed Science ◽

10.1017/wsc.2018.44 ◽

2018 ◽

Vol 66 (6) ◽

pp. 710-714

Author(s):

Vijay K. Varanasi ◽

Jason K. Norsworthy ◽

Chad Brabham ◽

Robert C. Scott

Keyword(s):

United States ◽

Resistance Mechanism ◽

Resistance Index ◽

Acetolactate Synthase ◽

Reduced Tillage ◽

Tillage Systems ◽

Als Inhibitors ◽

Inhibitor Resistance ◽

Als Inhibitor

AbstractPennsylvania smartweed [Persicaria pensylvanica(L.) M. Gómez] is a common weed of rice (Oryza sativaL.) in the midsouthern United States and has recently become a concern for farmers because of reduced tillage systems. Acetolactate synthase (ALS) inhibitors have been extensively used for controlling smartweeds in imidazolinone-resistant and conventional rice. In the present study, we confirmed resistance to commonly used ALS inhibitors in rice and characterized the underlying resistance mechanism in aP. pensylvanicabiotype from southeast Missouri. A dose–response experiment was conducted in the greenhouse using bensulfuron-methyl, imazethapyr, and bispyribac-sodium to determine the resistance index (resistance/susceptibility [R/S]) based on GR50estimates. The target-siteALSgene was amplified from R and S plants, and sequences were analyzed for mutations known to confer ALS-inhibitor resistance. TheP. pensylvanicabiotype in question was found to be resistant to bensulfuron-methyl (R/S=2,330), imazethapyr (R/S=12), and bispyribac-sodium (R/S=6). Sequencing of theALSgene from R plants revealed two previously known mutations (Pro-197-Ser, Ala-122-Ser) conferring resistance to sulfonylureas and imidazolinones. This is the first report of ALS-inhibitor resistance inP. pensylvanica.

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Target-site Mutation and Fitness Cost of Acetolactate Synthase Inhibitor-resistant Annual Bluegrass

HortScience ◽

10.21273/hortsci13512-18 ◽

2019 ◽

Vol 54 (4) ◽

pp. 701-705

Author(s):

Te-Ming Tseng ◽

Swati Shrestha ◽

James D. McCurdy ◽

Erin Wilson ◽

Gourav Sharma

Keyword(s):

Dna Sequencing ◽

Acetolactate Synthase ◽

Target Site ◽

Alternative Methods ◽

Resistance Level ◽

Annual Bluegrass ◽

Mechanism Of Resistance ◽

Als Inhibitors ◽

Inhibitor Resistance ◽

Als Inhibitor

Annual bluegrass (Poa annua L.) is an annual weed that is particularly troublesome in managed turfgrass. It has been controlled conventionally with herbicides, including acetolactate synthase (ALS) inhibitors. However, resistance to ALS inhibitors has been documented throughout the southeastern United States since 2012. A rate–response trial was conducted to confirm and determine the resistance level of suspected resistant P. annua biotypes from Mississippi (Reunion), followed by DNA sequencing to determine whether the mechanism of resistance is a target-site mutatio n. In addition, a fitness assay was conducted together with a susceptible biotype to determine whether resistance to ALS inhibitors is associated with decreased fitness. Reunion was at least 45 times more resistant to foramsulfuron than the standard susceptible biotype based on I50 estimates [I50 is the rate of herbicide giving a 50% response (50% visual necrosis)], requiring a predicted 331 g a.i./ha foramsulfuron for 50% control. DNA sequencing results identified a Trp574-to-Leu mutation in the ALS gene of the Reunion biotype, which has been shown by other studies to confer resistance to ALS inhibitors. Measurement of fitness parameters among the Reunion and susceptible biotypes demonstrated reduced seed yield, tillering, and flowering time in the resistant Reunion biotype, suggesting that ALS inhibitor resistance is possibly correlated to decreased fitness in P. annua. Alternative methods to control P. annua need to be considered as a result of the evolution of herbicide-resistant biotypes. An integrated management strategy to control P. annua weeds will help prevent further evolution of resistance. Because this study evaluated only the target-site mechanism of resistance, it is also necessary to determine whether the resistant biotype has reduced uptake, translocation, or enhanced metabolism as additional mechanisms of resistance. Consequently, a fitness study encompassing a more comprehensive list of plant parameters will provide conclusions of the fitness costs associated with ALS inhibitor resistance in P. annua. Chemical names: Foramsulfuron {1-(4,6-dimethoxypyrimidin-2-yl)-3-[2-(dimethylcarbamoyl)-5-formamidophenylsulfonyl] urea}.

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Glyphosate and acetolactate synthase inhibitor resistance in Russian thistle (Salsola tragus L.) in Alberta

Canadian Journal of Plant Science ◽

10.1139/cjps-2018-0252 ◽

2019 ◽

Vol 99 (3) ◽

pp. 384-387

Author(s):

Hugh J. Beckie ◽

Linda M. Hall ◽

Scott W. Shirriff ◽

Elise Martin ◽

Julia Y. Leeson

Keyword(s):

Acetolactate Synthase ◽

Glyphosate Resistance ◽

Synthase Inhibitor ◽

Inhibitor Resistance ◽

Als Inhibitor

A survey was conducted in Alberta in 2017 to determine the distribution and abundance of acetolactate synthase (ALS) inhibitor and glyphosate resistance in Russian thistle. Of 45 populations tested, 31 (62%) were ALS inhibitor resistant. No populations exhibited resistance to glyphosate. This survey serves as a baseline to monitor future incidence of resistance in this weed.

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