No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Prevalence of cross- or multiple resistance to the acetyl-coenzyme A carboxylase inhibitors fenoxaprop, clodinafop and pinoxaden in black-grass (Alopecurus myosuroides Huds.) in France
Pest Management Science
Abstract
Repeated use of acetyl-CoA carboxylase (ACCase) inhibitors, especially fenoxaprop and clodinafop, since the late 1980s has selected for resistance in Alopecurus myosuroides Huds. (black-grass) in France. We investigated whether resistance to pinoxaden, a phenylpyrazoline ACCase inhibitor to be marketed in France, was present in French black-grass populations. We investigated pinoxaden resistance conferred by five mutant ACCase isoforms. Using 84 French black-grass field samples, we also compared the frequencies of other mechanisms endowing resistance to fenoxaprop, clodinafop or pinoxaden.
ACCase mutant isoforms Leu-1781, Gly-2078 and, likely, Cys-2027 conferred cross-resistance to pinoxaden, while isoform Asn-2041 possibly conferred moderate resistance. Other mechanisms of resistance to fenoxaprop, clodinafop and pinoxaden were detected in 99, 68 and 64% of the samples investigated, respectively. Cross- or multiple resistance to fenoxaprop or clodinafop and pinoxaden was not systematically observed, suggesting a diversity of mechanisms exist.
Pinoxaden resistance was observed before pinoxaden release in France. Only a fraction of the mechanisms endowing fenoxaprop or clodinafop resistance also confer pinoxaden resistance. Pinoxaden resistance was likely mostly selected for by ACCase inhibitors, and, in some cases, possibly by herbicides with other modes of action. This illustrates the necessity to use metabolisable herbicides cautiously where black-grass has evolved non-target-site-based resistance.
... Allelic variants in ACCase genes are the most commonly reported TSR mechanisms and have been characterized as yielding resistance in different kinds of grass weeds, including Alopecurus spp. (Petit et al. 2010), American sloughgrass [Beckmannia syzigachne (Steud.) Fernald] (Tang et al. 2015), Echinochloa spp. ...
... It should also be noted that none of the four herbicides with other MOAs could kill the S population if they were applied at rates below the recommended field dosage recommended (data not shown), suggesting these herbicides were unable to control this weed due to poor effectiveness. Based on the results, we concluded that the Ile-1781-Leu substitution conferred wide-spectrum resistance to all of the APP, CHD, and DEN herbicides tested, which is in line with previous research in other weed species (Basak et al. 2020;Deng et al. 2019;Petit et al. 2010;Yu et al. 2007). Ile-1781 is within a domain close to the binding site for ACCase herbicides across three chemical groups, explaining the resistance spectrum to all three families (Beckie and Tardif 2012;Gaines et al. 2020). ...
Barnyardgrass [ Echinochloa crus-galli (L.) P. Beauv.] is increasingly infesting imidazolinone-tolerant (IMI-T) rice fields in China, imazamox resistance of E. crus-galli has become the major concern for weed management in IMI-T rice fields. In this study, the susceptible population JLGY-3 (S) and the suspected resistant population JHXY-2 (R) collected from IMI-T rice fields were used as research subjects. When treated with imazamox, JHXY-2 (R) population showed a high level of herbicide resistance with a resistance index (RI) of 31.2. JHXY-2 (R) was cross-resistant to all five acetolactate synthase (ALS) inhibitors from different chemical families, but sensitive to herbicides inhibiting acetyl-CoA carboxylase (ACCase). In order to understand the reason why JHXY-2 (R) was resistant to imazamox, we performed experiments to characterize potential TSR and NTSR mechanisms. A trp-574-leu amino acid mutation in ALS and low imazamox ALS sensitivity were the main mechanism underlying imazamox resistance in this JHXY-2 (R) population. There was no significant difference in ALS gene expression and ALS protein abundance between R and S populations. High-performance liquid chromatography-tandem mass spectrometry analysis showed enhanced metabolism of imazamox in JHXY-2 (R), which was in contrast to the results of pretreatment with a metabolic enzyme inhibitor. Treatments with the P450/GST inhibitors did not alter the resistance level of JHXY-2 (R) against imazamox. To further clarify the NTSR mechanism of JHXY-2 (R), transcriptome sequencing showed that there was almost no significant difference in the expression of P450 and GST metabolic enzyme genes between R and S populations, and only GST-U1 showed a significant induction in R population. In conclusion, amino acid mutation and higher enzyme activity of ALS are the main causes of imazamox resistance in JHXY-2 (R). However, given the differences in imazamox residues in the leaves of the E. crus-galli , there may still be undetectable NTSR that are causing imazamox resistance in the R population.
... Allelic variants in ACCase genes are the most commonly reported TSR mechanisms and have been characterized as yielding resistance in different kinds of grass weeds, including Alopecurus spp. (Petit et al. 2010), American sloughgrass [Beckmannia syzigachne (Steud.) Fernald] (Tang et al. 2015), Echinochloa spp. ...
... It should also be noted that none of the four herbicides with other MOAs could kill the S population if they were applied at rates below the recommended field dosage recommended (data not shown), suggesting these herbicides were unable to control this weed due to poor effectiveness. Based on the results, we concluded that the Ile-1781-Leu substitution conferred wide-spectrum resistance to all of the APP, CHD, and DEN herbicides tested, which is in line with previous research in other weed species (Basak et al. 2020;Deng et al. 2019;Petit et al. 2010;Yu et al. 2007). Ile-1781 is within a domain close to the binding site for ACCase herbicides across three chemical groups, explaining the resistance spectrum to all three families (Beckie and Tardif 2012;Gaines et al. 2020). ...
Digitaria ciliaris var. chrysoblephara (Fig. & De Not.) R.R. Stewart is an annual xeromorphic weed that severely infests direct-seeded rice fields in China. Herbicide resistance is emerging in D. ciliaris var. chrysoblephara owing to extensive and recurrent use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicide metamifop. In this study, a total of 53 D. ciliaris var. chrysoblephara populations randomly sampled from direct-seeded rice fields across Jiangsu Province were investigated for metamifop resistance and potential resistance-endowing mutations. Single-dose assays revealed that 17 (32.1%) populations evolved resistance to metamifop and 5 (9.4%) populations were in the process of developing resistance. Resistance index (RI) of metamifop-resistant populations ranged from 2.7 to 32.1. Amino acid substitutions (Ile-1781-Leu, Trp-2027-Cys/Ser, and Ile-2041-Asn) in ACCase genes were detected in resistant D. ciliaris var. chrysoblephara plants, and caused various cross-resistance patterns to ACCase-inhibiting herbicides. All of four resistant populations (YC07, YZ09, SQ03, and HA06), with different ACCase mutations, exhibited cross-resistance to the aryloxyphenoxypropionate (APP) herbicides cyhalofop-butyl (RIs, 10.0 to 19.9), fenoxaprop-P-ethyl (RIs, 53.7 to 132.8), and haloxyfop-P-methyl (RIs, 6.2 to 62.6), and the phenylpyrazoline (DEN) pinoxaden (RIs, 2.3 to 5.4), but responded differently to the cyclohexanedione (CHD) herbicides clethodim and sethoxydim. It is noteworthy that four post-emergence herbicides used for rice cropping, including bispyribac-sodium, pyraclonil, quinclorac, and anilofos, showed poor control effect against D. ciliaris var. chrysoblephara, suggesting few alternations for managing this weed in rice fields except ACCase inhibitors. In conclusion, this work demonstrated that the D. ciliaris var. chrysoblephara had developed resistance to ACCase-inhibiting herbicides in rice cultivation of China, and target-site amino acid substitutions in ACCase were primarily responsible for metamifop resistance.
... It has been previously suggested that the resistance patterns observed in grasses could be explained by amino acid substitutions in ACCase (Powles & Yu, 2010). For instance, it is generally assumed that amino acid changes at position 1781 will confer resistance to herbicides in all three chemical groups of ACCase inhibitors based on previous work in Alopecurus myosuroides (Petit et al., 2010) and ...
... Lolium rigidum (Zhang & Powles, 2006), while substitution at position 2078 confers resistance to all chemical groups in A. myosuroides (Petit et al., 2010), L. multiflorum (Kaundun, 2010), L. rigidum (Yu et al., 2007), and P. paradoxa (Hochberg et al., 2009 (Table S4). The complexity in resistance patterns could be explained by additional polymorphisms in the ACCase gene (other than those known to confer ACCase inhibitor resistance). ...
Herbicide resistance in weeds is one of the greatest challenges in modern food production. The grass species Lolium multiflorum is an excellent model species to investigate evolution under similar selection pressure because populations have repeatedly evolved resistance to many herbicides, utilizing a multitude of mechanisms to neutralize herbicide damage. In this work, we investigated the gene that encodes acetyl‐CoA carboxylase (ACCase), the target site of the most successful herbicide group available for grass weed control. We sampled L. multiflorum populations from agricultural fields with history of intense herbicide use, and studied their response to three ACCase‐inhibiting herbicides. To elucidate the mechanisms of herbicide resistance and the genetic relationship among populations, we resolved the haplotypes of 97 resistant and susceptible individuals by sequencing ACCase amplicons using long‐read DNA sequencing technologies. Our dose–response data indicated the existence of many, often unpredictable, resistance patterns to ACCase‐inhibiting herbicides, where populations exhibited as much as 37‐fold reduction in herbicide response. The majority of the populations exhibited resistance to all three herbicides studied. Phylogenetic and molecular genetic analyses revealed multiple evolutionary origins of resistance‐endowing ACCase haplotypes, as well as widespread admixture in the region regardless of cropping system. The amplicons generated were diverse, with haplotypes exhibiting 26–110 polymorphisms. Polymorphisms included insertions and deletions 1–31 bp in length, none of which were associated with the resistance phenotype based on an association analysis. We also found evidence that some populations have multiple mechanisms of resistance. Our results highlight the astounding genetic diversity in L. multiflorum populations, and the potential for repeated evolution of herbicide resistance across the landscape that challenges weed management approaches and jeopardizes sustainable weed control practices. We provide an in‐depth discussion of the evolutionary and practical implications of our results.
... Unlike Ile2041Thr, the Ile2041Asn and Ile2041Val mutations, which are the most common mutations at this position reported to date, have been identified in several weed species including A. myosuroides, 29 A. fatua, 30 A. sterilis L., 31 Lolium rigidum Gaud., 29,32 Phalaris paradoxa L., 33 Sorghum halepense (L.) Pers. 34 The ACCase resistance-endowing Gly2096Ala mutation has been found in populations of several resistant weed species including A. fatua, 35 A. myosuroides, 16,36 Beckmannia syzigachne (Steud.), 37,38 Diplachne fusca (L.) P.Beauv. ...
... 41 In contrast, A. myosuroides populations carrying the Gly2096Ala mutation were resistant to APP herbicides but susceptible to CHD and PPZ herbicides. 36,42 In our study, it was also observed differences in the cross-resistance patterns of the resistant B. tectorum populations with this mutation. Populations UDB-1, UDB-2, UDB-3, UDB-4, and UDB-7 were cross-resistant to all APP and CHD herbicides tested. ...
Background
The prevalent and repeated use of acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides for Bromus tectorum L. control in fine fescue (Festuca L. spp) grown for seed has selected ACCase‐resistant B. tectorum populations. The objectives of this study were to (1) evaluate the response of nine B. tectorum populations to the ACCase inhibitors clethodim, sethoxydim, fluazifop‐P‐butyl, and quizalofop‐P‐ethyl and the acetolactate synthase (ALS) inhibitor sulfosulfuron and (2) characterize the resistance mechanisms.
Results
Bromus tectorum populations were confirmed to be resistant to the ACCase‐inhibiting herbicides tested. The levels of resistance varied among the populations for clethodim (resistance ratio, RR = 5.1–14.5), sethoxydim (RR = 18.7–44.7), fluazifop‐P‐butyl (RR = 3.1–40.3), and quizalofop‐P‐ethyl (RR = 14.5–36). Molecular investigations revealed that the mutations Ile2041Thr and Gly2096Ala were the molecular basis of resistance to the ACCase‐inhibiting herbicides. The Gly2096Ala mutation resulted in cross‐resistance to the aryloxyphenoxypropionate (APP) herbicides fluazifop‐P‐butyl and quizalofop‐P‐ethyl, and the cyclohexanedione (CHD) herbicides clethodim, and sethoxydim, whereas Ile2041Thr mutation resulted in resistance only to the two APP herbicides. All B. tectorum populations were susceptible to sulfosulfuron (RR = 0.3–1.7).
Conclusions
This is the first report of target‐site mutations conferring resistance to ACCase‐inhibiting herbicides in B. tectorum. The results of this study suggest multiple evolutionary origins of resistance and contribute to understanding the patterns of cross‐resistance to ACCase inhibitors associated with different mutations in B. tectorum. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... Herbicide resistance can be conferred by two general mechanisms: target-site resistance (TSR) and non-target site resistance (NTSR) (Petit et al. 2010;Yuan et al. 2007). TSR is due to a deletion of an amino acid or substitutions of different amino acids in the herbicide target protein, which may prevent the occurrence of herbicide interactions (Dayan et al. 2018;Kukorelli et al. 2013;Petit et al. 2010). ...
... Herbicide resistance can be conferred by two general mechanisms: target-site resistance (TSR) and non-target site resistance (NTSR) (Petit et al. 2010;Yuan et al. 2007). TSR is due to a deletion of an amino acid or substitutions of different amino acids in the herbicide target protein, which may prevent the occurrence of herbicide interactions (Dayan et al. 2018;Kukorelli et al. 2013;Petit et al. 2010). Target-site mutations contribute to P. annua resistance to ACCase, ALS, microtubule-assembly, PSII, and EPSPS inhibitors (Barua et al. 2020;Cross et al. 2015;Délye and Michel 2005;McElroy et al. 2013;Svyantek et al. 2016;Tseng et al. 2019). ...
The mitotic-inhibiting herbicide pronamide controls susceptible annual bluegrass ( Poa annua L.) pre- and post-emergence, but in some resistant populations, post-emergence activity is compromised, hypothetically due to a target-site mutation, lack of root uptake, or an unknown resistance mechanism. Three suspected pronamide-resistant (LH-R, SC-R, and SL-R) and two pronamide-susceptible (BS-S and HH-S) populations were collected from Mississippi golf courses. Dose-response experiments were conducted to confirm and quantify pronamide resistance, as well as resistance to flazasulfuron and simazine. Target-sites known to confer resistance to mitotic-inhibiting herbicides were sequenced, as were target-sites for herbicides inhibiting acetolactate synthase (ALS) and photosystem II (PSII). Pronamide absorption, and translocation was investigated following foliar and soil applications. Dose-response experiments confirmed pronamide resistance of LH-R, SC-R, and SL-R populations, as well as instances of multiple resistance to ALS and PSII inhibiting herbicides. Sequencing of the α-tubulin gene confirmed the presence of a mutation that substituted isoleucine for threonine at position 239 (Thr239-Ile) in LH-R, SC-R, SL-R, and BS-S populations. Foliar application experiments failed to identify differences in pronamide absorption and translocation between the five populations, regardless of harvest time. All populations had limited basipetal translocation—only 3–13% of the absorbed pronamide—across harvest times. Soil application experiments revealed that pronamide translocation was similar between SC-R, SL-R, and both susceptible populations across harvest times. The LH-R population translocated less soil-applied pronamide than susceptible populations, 24, 72, and 168 HAT, suggesting that reduced acropetal translocation may contribute to pronamide resistance. This study reports three new pronamide-resistant populations, two of which are resistant to two modes-of-action (MOA), and one of which is resistant to three MOA. Results suggest that both target-site- and translocation-based mechanisms may be associated with pronamide resistance. Further research is needed to confirm the link between pronamide resistance and the Thr239-Ile mutation of the α-tubulin gene.
... 7 NTSR is mostly selected by ACCase-inhibiting chemical groups and in some cases also by herbicides with other modes of action. 8,9 The enhanced herbicide metabolism is a major NTSR mechanism, which involves the activation of expression of multiple genes and gene families including cytochrome P450 monooxygenases (CYP450s), glutathione S-transferases (GSTs), ABC transporters (ABCs), glycosyltransferases (GTs), oxidases, and esterases. Additionally, the role of transcriptional control by transcription factors and the regulation at the post-translational level involving protein-activating proteins (kinases or phosphatases) was raised. ...
... TSR mechanism was also reported to contribute to a lesser extent to the resistance against pinoxaden. 9 The mechanisms underlying NTSR associated with gene expression changes have been studied in several weed species by nextgeneration sequencing (RNA-Seq), e.g. Alopecurus myosuroides, Lolium rigidum, Cicer arietinum, or Echinochloa crus-galli. ...
Background
The continuous use of the herbicides contributes to the emergence of the resistant populations of numerous weed species that are tolerant to multiple herbicides with different modes of action (multiple resistance) which is provided by non‐target‐site resistance mechanisms. In this study, we addressed the question of rapid acquisition of herbicide resistance to pinoxaden (acetyl CoA carboxylase inhibitor) in Apera spica‐venti, which endangers winter cereal crops and has high adaptation capabilities to inhabit many rural locations. To this end, de novo transcriptome of Apera spica‐venti was assembled and RNA‐sequencing analysis of plants resistant and susceptible to pinoxaden treated with this herbicide was performed.
Results
The obtained data showed that the prime candidate genes responsible for herbicide resistance were those encoding 3‐ketoacyl‐CoA synthase 12‐like, UDP‐glycosyltransferases (UGT) including UGT75K6, UGT75E2, UGT83A1‐like, and glutathione S‐transferases (GSTs) such as GSTU1 and GSTU6. Also, such highly accelerated herbicide resistance emergence may result from the enhanced constitutive expression of a wide range of genes involved in detoxification already before herbicide treatment and may also influence response to biotic stresses, which was assumed by the detection of expression changes in genes encoding defence‐related proteins, including receptor kinase‐like Xa21. Moreover, alterations in the expression of genes associated with methylation in non‐treated herbicide‐resistant populations were identified.
Conclusion
The obtained results indicated genes that may be involved in herbicide resistance. Moreover, they provide valuable insight into the possible effect of resistance on the weed interaction with the other stresses by indicating pathways associated with both abiotic and biotic stresses. © 2023 Society of Chemical Industry.
... In this study, the AH93 A. myosuroides population could survive the pinoxaden application at 4× the field rate (240 g ha −1 ) and the Trp-2027-Cys and Arg-2088-Cys amino acid mutations were identified. The Trp-2027-Cys mutation has been reported in many grass weed species, such as Digitaria insularis [21] and Rottboellia cochinchinensis [22]. A. myosuroides with Trp-2027-Cys mutation from France could withstand pinoxaden application in the field rate (60 g ha −1 ) and showed cross-resistance to fenoxaprop and clodinafop [23]. In addition, The Cys-2088- ...
... In this study, the AH93 A. myosuroides population could survive the pinoxaden application at 4× the field rate (240 g ha −1 ) and the Trp-2027-Cys and Arg-2088-Cys amino acid mutations were identified. The Trp-2027-Cys mutation has been reported in many grass weed species, such as Digitaria insularis [21] and Rottboellia cochinchinensis [22]. A. myosuroides with Trp-2027-Cys mutation from France could withstand pinoxaden application in the field rate (60 g ha −1 ) and showed crossresistance to fenoxaprop and clodinafop [23]. In addition, The Cys-2088-Arg mutation is consistent with the findings of Papapanagiotou et al. [24], who reported that Cys-2088-Arg amino acid substitutions conferred resistance to ACCase herbicides in Avena sterilis. ...
Black grass (Alopecurus myosuroides Huds.) is a highly competitive weed in winter wheat fields of China. Due to repeated use of acetolactate synthase (ALS) inhibitors, many A. myosuroides populations have evolved resistance to pyroxsulam in some wheat fields. Research was conducted to determine the molecular basis of herbicide resistance in the AH93 A. myosuroides population. Whole-plant dose–response assay confirmed that the AH93 population was resistant to pyroxsulam with a resistance index of 4.2. Cross- and multiple-resistance assays indicated that the AH93 population was cross-resistant to mesosulfuron-methyl and multiple-resistant to pinoxaden. Sequencing of the ALS and ACCase gene revealed that there was no target-site mutation in ALS, but Trp-2027-Cys and Cys-2088-Arg amino acid mutations in ACCase in the AH93 population. A malathion pretreatment study indicated that the AH93 population might have cytochrome P450–mediated herbicide metabolic resistance. This is the first report of pyroxsulam resistance in a multiple-resistant A. myosuroides population in China, and the Cys-2088-Arg mutation is the first reported case of an ACCase mutant conferring herbicide resistance in A. myosuroides.
... Some forms of wintering Avena ludoviciana L. (Uludag et al., 2008;Sasanfar et al., 2009) and of Alopecurus myosuroides Huds. (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
... (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
The action of some foliar herbicides and herbicide combinations for control of common wheat (Triticum aestivum L.) weeds was studied. To that end against the background of soil applied Stomp 330EK New at a dose of 5 l/ha the herbicides Axial 050EK, Granstar 75DF, Derby Super WG, Sekator OD, Lintur 70WG, and the tank mixtures of Axial with the other herbicides applied in the tillering phenophase of the crop were studied. The species composition and density of weeds was assessed using the quantitative method prior to treatment and after herbicide treatment on days 5, 15 and 30, by constant metering. The herbicide Lintur 70WG and its combination with Axial 050EK had the fastest initial effect. The highest herbicidal effect (99.5%) against annual monocotyledon and dicotyledon weeds showed the combination of Derby Super WG 33 g/ha + Axial 050EK-900 ml/ha. Very good was the effect of the other herbicidal mixtures between anti-broadleaf herbicides and the graminaceous herbicide Axial 050. All applied herbicides and herbicide mixtures showed a very good after-action on weeds.
... Some forms of wintering Avena ludoviciana L. (Uludag et al., 2008;Sasanfar et al., 2009) and of Alopecurus myosuroides Huds. (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
... (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
The action of some foliar herbicides and herbicide combinations for control of common wheat (Triticum aestivum L.) weeds was studied. To that end against the background of soil applied Stomp 330EK New at a dose of 5 l/ha the herbicides Axial 050EK, Granstar 75DF, Derby Super WG, Sekator OD, Lintur 70WG, and the tank mixtures of Axial with the other herbicides applied in the tillering phenophase of the crop were studied. The species composition and density of weeds was assessed using the quantitative method prior to treatment and after herbicide treatment on days 5, 15 and 30, by constant metering. The herbicide Lintur 70WG and its combination with Axial 050EK had the fastest initial effect. The highest herbicidal effect (99.5%) against annual monocotyledon and dicotyledon weeds showed the combination of Derby Super WG 33 g/ha + Axial 050EK-900 ml/ha. Very good was the effect of the other herbicidal mixtures between anti-broadleaf herbicides and the graminaceous herbicide Axial 050. All applied herbicides and herbicide mixtures showed a very good after-action on weeds.
... To reduce the probability of evolution of resistance to auxinic herbicides, proper crop rotation, as well as other components of integrated weed management, should be applied. As was shown before, the over-use of one herbicide can eventually lead to resistance to several other herbicides from the same MOA [36,37]. According to the records of herbicide applications received from the farmers, extensive and prolonged use of tribenuron-methyl and iodosulfuron was documented in fields were DER and EHR populations were found. ...
... This report should increase the awareness and alert farmers and researchers in the region and beyond in order to proactively challenge the evolution of herbicide resistance in D. erucoides and E. hispanica in arable crops. As was shown before, the over-use of one herbicide can eventually lead to resistance to several other herbicides from the same MOA [36,37]. According to the records of herbicide applications received from the farmers, extensive and prolonged use of tribenuron-methyl and iodosulfuron was documented in fields were DER and EHR populations were found. ...
Diplotaxis erucoides and Erucaria hispanica are common weeds of the Mediterranean region; they infest various habitats including cultivated fields and roadsides. In several fields across Israel, farmers have reported on poor control of D. erucoides and E. hispanica plants using acetolactate synthase (ALS) inhibitors. Greenhouse experiments were conducted to determine the effect of various ALS inhibitors on plants from two potentially resistant D. erucoides and E. hispanica populations. Additionally, alternative management strategies using auxinic herbicides were studied. Plants from both populations exhibited resistance to all tested ALS inhibitors, up to 20-fold the label field rate, as compared with ALS sensitive populations of D. erucoides and E. hispanica. Sequencing of the ALS gene revealed Trp574 to Leu substitution in ALS-resistant D. erucoides plants, whereas a Pro197 to Ser substitution was detected in ALS-resistant E. hispanica plants. Although high levels of resistance were observed in individuals from both putative resistant populations, sensitive individuals were also detected, suggesting the evolution of resistance in these two populations is still in progress. Auxinic herbicides, 2,4-D, and mecoprop-P, provided excellent control of plants from both ALS-resistant populations. This study documents and confirms the first case of evolution of resistance to ALS inhibitors in D. erucoides and E. hispanica populations.
... Some forms of wintering Avena ludoviciana L. (Uludag et al., 2008;Sasanfar et al., 2009) and of Alopecurus myosuroides Huds. (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
... (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
The action of some foliar herbicides and herbicide combinations for control of common wheat (Triticum aestivum L.) weeds was studied. To that end against the background of soil applied Stomp 330EK New at a dose of 5 l/ha the herbicides Axial 050EK, Granstar 75DF, Derby Super WG, Sekator OD, Lintur 70WG, and the tank mixtures of Axial with the other herbicides applied in the tillering phenophase of the crop were studied. The species composition and density of weeds was assessed using the quantitative method prior to treatment and after herbicide treatment on days 5, 15 and 30, by constant metering. The herbicide Lintur 70WG and its combination with Axial 050EK had the fastest initial effect. The highest herbicidal effect (99.5%) against annual monocotyledon and dicotyledon weeds showed the combination of Derby Super WG 33 g/ha + Axial 050EK-900 ml/ha. Very good was the effect of the other herbicidal mixtures between anti-broadleaf herbicides and the graminaceous herbicide Axial 050. All applied herbicides and herbicide mixtures showed a very good after-action on weeds.
... Some forms of wintering Avena ludoviciana L. (Uludag et al., 2008;Sasanfar et al., 2009) and of Alopecurus myosuroides Huds. (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
... (Petit et al., 2010;Delye, 2011) were reported to be resistant to pinoxaden. In a study of Alopecurus myosuroides Huds., resistance was reported to fenoxaprop-P-ethyl 99%, to clodinafop -68% and to pinoxaden -64%, respectively (Petit et al., 2010). ...
The action of some foliar herbicides and herbicide combinations for control of common wheat (Triticum aestivum L.) weeds was studied. To that end against the background of soil applied Stomp 330EK New at a dose of 5 l/ha the herbicides Axial 050EK, Granstar 75DF, Derby Super WG, Sekator OD, Lintur 70WG, and the tank mixtures of Axial with the other herbicides applied in the tillering phenophase of the crop were studied. The species composition and density of weeds was assessed using the quantitative method prior to treatment and after herbicide treatment on days 5, 15 and 30, by constant metering. The herbicide Lintur 70WG and its combination with Axial 050EK had the fastest initial effect. The highest herbicidal effect (99.5%) against annual monocotyledon and dicotyledon weeds showed the combination of Derby Super WG 33 g/ha + Axial 050EK-900 ml/ha. Very good was the effect of the other herbicidal mixtures between anti-broadleaf herbicides and the graminaceous herbicide Axial 050. All applied herbicides and herbicide mixtures showed a very good after-action on weeds.
... Due to the availability of molecular biology techniques and publications of ACCase target genes, as well as the availability of DNA markers related to the most commercially valuable weeds, the resistance mechanism of target loci to ACCase herbicides has been extensively studied in the past decade (Délye and Michel, 2005;Kaundun, 2006). Until now, seven amino acid substitutions in the CT domain of ACCase have been documented to endow ACCase-inhibitor herbicide resistance in grass weed: Ile1781 to Leu or Val (Délye et al., 2001;Delye et al., 2002;Delye, 2003;Collavo et al., 2011;Mohamed, 2012;Li et (Kaundun et al., 2013;Liu et al., 2007), Trp2027 to Cys (Delye, 2005;Yu et al., 2007;Petit et al., 2010;Beckie and Sauder, 2012;Xu et al., 2013), Ile2041 to Asn or Val (Delye, 2003;Liu et al., 2007;Cruz-Hipolito et al., 2011;Tang et al., 2012), Asn2078 to Gly (Liu et al., 2007;Delye, 2005;Petit et al., 2010;Hochberg and Rubin, 2009;Kaundun, 2010), Cys2088 to Arg (Delye, 2005;Yu et al., 2007;Beckie and Sauder, 2012;Scarabel et al., 2011;Kaundun et al., 2012) and Gly2096 to Ala or Ser (Delye, 2005;Beckie and Sauder, 2012;Kaundun et al., 2012). ...
... Due to the availability of molecular biology techniques and publications of ACCase target genes, as well as the availability of DNA markers related to the most commercially valuable weeds, the resistance mechanism of target loci to ACCase herbicides has been extensively studied in the past decade (Délye and Michel, 2005;Kaundun, 2006). Until now, seven amino acid substitutions in the CT domain of ACCase have been documented to endow ACCase-inhibitor herbicide resistance in grass weed: Ile1781 to Leu or Val (Délye et al., 2001;Delye et al., 2002;Delye, 2003;Collavo et al., 2011;Mohamed, 2012;Li et (Kaundun et al., 2013;Liu et al., 2007), Trp2027 to Cys (Delye, 2005;Yu et al., 2007;Petit et al., 2010;Beckie and Sauder, 2012;Xu et al., 2013), Ile2041 to Asn or Val (Delye, 2003;Liu et al., 2007;Cruz-Hipolito et al., 2011;Tang et al., 2012), Asn2078 to Gly (Liu et al., 2007;Delye, 2005;Petit et al., 2010;Hochberg and Rubin, 2009;Kaundun, 2010), Cys2088 to Arg (Delye, 2005;Yu et al., 2007;Beckie and Sauder, 2012;Scarabel et al., 2011;Kaundun et al., 2012) and Gly2096 to Ala or Ser (Delye, 2005;Beckie and Sauder, 2012;Kaundun et al., 2012). ...
... They observed cross-resistance between haloxyfop and pinoxaden, but not to clethodim. This is not an uncommon cross-resistance pattern, and it has been observed in other species such as A. myosuroides (Petit et al. 2010) and L. multiflorum (Brunharo and Tranel 2023). This pattern is different from the one we observed in our project, in that cross-resistance across all chemical classes of ACCase inhibitors was detected. ...
Sourgrass [ Digitaria insularis (L.) Mez ex Ekman] is considered the most troublesome weed in agronomic crops in South America. Overreliance on glyphosate has selected for resistant populations, although the resistance mechanisms remain unknown. Recently, populations were identified that exhibited multiple resistance to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and acetyl-CoA carboxylase (ACCase) inhibitors, posing a significant challenge due to the lack of alternative control options. This project aimed to identify the resistance patterns and levels to glyphosate and ACCase inhibitors of three suspected resistant populations (P1, P2, and P3), and elucidate the resistance mechanisms. We performed dose–response experiments with clethodim, fluazifop-P-butyl, glyphosate, and pinoxaden to identify the possibility of cross- and multiple resistance and to quantify the resistance levels. We sequenced the ACCase and EPSPS genes to test the hypothesis that target-site mutations were involved in the resistance mechanisms, given the resistance patterns observed. Our results indicated that two of the tested populations, P1 and P2, were multiple resistant to glyphosate and all ACCase-inhibitor classes, while P3 was resistant to glyphosate only. Resistance levels varied by herbicide, with resistance indices ranging from 2.7- to nearly 2,000-fold. We identified an amino acid substitution in ACCase at position 2078 (Asp-2078-Gly), homozygous for both P1 and P2, corroborating the resistance patterns observed. Interestingly, EPSPS sequencing identified multiple heterozygous DNA polymorphisms that resulted in amino acid substitutions at positions 106 (P1 and P2) or at both 102 and 106 (P3), indicating multiple evolutionary origins of glyphosate-resistance evolution. We show for the first time the genetic mechanisms of multiple resistance to glyphosate and ACCase in D. insularis , and provide a thorough discussion of the evolutionary and management implications of our work.
... Of particular importance is the extent to which prior selection with other actives might have pre-selected for resistance to the newer chemistry. As an example, Petit et al. 8 identified pinoxaden resistance in French populations of A. myosuroides before pinoxaden was released in France, while quinclorac resistance was observed in Californian populations of Echinochloa phyllopogon without any prior exposure to this herbicide. 9 Non-target-site resistance (NTSR) mechanisms are of particular concern in this regard, due to their potential to result in broad and unpredictable cross-resistance, across structurally different herbicide groups. ...
BACKGROUND
Cinmethylin is an inhibitor of plant fatty acid biosynthesis, with in‐plant activity caused by its binding to fatty acid thioesterases (FATs). The recent registration of cinmethylin for pre‐emergence herbicidal use in the UK represents a new mode‐of‐action (MOA) for control of the grassweed blackgrass (Alopecurus myosuroides). To date there is little published information on the extent of blackgrass' inter‐population variability in sensitivity to cinmethylin, nor on any potential effect of existing non‐target‐site resistance (NTSR) mechanisms on cinmethylin efficacy.
RESULTS
Here we present a study of variability in cinmethylin sensitivity amongst 97 UK blackgrass populations. We demonstrate that under controlled conditions, a UK field‐rate dose of 500 g ha⁻¹ provides effective control of the tested populations. Nevertheless, we reveal significant inter‐population variability at doses below this rate, with populations previously characterised as strongly NTSR displaying the lowest sensitivity to cinmethylin. Assessment of paired resistant ‘R’ and sensitive ‘S’ lines from standardised genetic backgrounds confirms that selection for NTSR to the acetyl‐CoA‐carboxylase inhibitor fenoxaprop, and the microtubule assembly inhibitor pendimethalin, simultaneously results in reduced sensitivity to cinmethylin at doses below 500 g ha⁻¹. Whilst we find no resistance to the field‐rate dose, we reveal that cinmethylin sensitivity can be further reduced through experimental selection with cinmethylin.
CONCLUSION
Cinmethylin therefore represents a much‐needed further MOA for blackgrass control, but needs to be carefully managed within a resistance monitoring and integrated weed management (IWM) framework to maximise the effective longevity of this compound. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... In some cases, there is a co-existence of both TSRs and NTSRs, such as in Lolium multiflorum involvement of cytochrome P450 and presence of single point mutation, enhanced metabolism, and target gene overexpression in Bromus sterilis and P450s-involved enhanced metabolism and target-site gene mutation in ACCase resistant Rapistrum rugosum (Hatami et al. 2016, Sen et al. 2021, Wu et al. 2022. The coexistence of TSR and NTSR mechanisms in black grass has also been anticipated by Petit et al. (2010). Among the TSR mutations, to date, eight functional sites within the ALS enzyme (Ala122, Pro197, Ala205, Asp376, Arg377, Trp574, Ser653 and Gly654) have been identified in weed species that are known to confer resistance against ALS-inhibiting herbicides (Powles and Yu 2010). ...
... NTSR mechanisms can be the result of physiological and biochemical alterations such as reduced herbicide absorption and translocation, enhanced herbicide metabolism, and herbicide vacuolar sequestration (Jugulam and Shyam 2019;Yuan et al. 2007). NTSR is of particular concern, because it can confer resistance to herbicides from different chemical families across multiple sites of action (SOAs), including herbicides not commercially available (Ma et al. 2013;Petit et al. 2010;Preston 2003), thus limiting the herbicide options for weed control. ...
This review summarizes what is currently known about herbicide resistance in Bromus spp. worldwide. Additional information on the biology and genetics of Bromus spp. is provided to further the understanding of resistance evolution and dispersal of the different species. Cases of herbicide resistance have been confirmed in Bromus catharticus Vahl., Bromus commutatus Schrad.; syn. Bromus racemosus L., Bromus diandrus Roth, Bromus japonicus Thunb.; syn. Bromus arvensis L., Bromus madritensis L., Bromus rigidus Roth; syn. Bromus diandrus Roth ssp. diandrus , Bromus rubens L., Bromus secalinus L., Bromus sterilis L., and Bromus tectorum L. in 11 countries. Bromus spp. populations have evolved cross and multiple-resistance to six herbicide sites of action: acetyl-coenzyme A carboxylase, acetolactate synthase, photosystem II, very long-chain fatty acid, 5-enolpyruvylshikimate-3-phosphate synthase, and 4-hydroxyphenylpyruvate dioxygenase inhibitors. Resistance mechanisms varied from target-site to non-target-site or a combination of both. Bromus spp. are generally highly self-pollinated, but outcrossing can occur at low levels in some species. Bromus spp. have different ploidy levels, ranging from diploid (2 n = 2 x = 14) to duodecaploid (2 n = 12 x = 84). Herbicide resistance in Bromus spp. is a global issue, and the spread of herbicide resistance alleles primarily occurs via seed-mediated gene flow. However, the transfer of herbicide resistance alleles via pollen-mediated gene flow is possible.
... This applies to the ACCase inhibitor clodinafop-propargyl and its active metabolite clodinafop-acid, which more frequently lose efficacy due to target site resistance e.g., in American sloughgrass (Beckmannia syzigachne) 59 and in black-grass. 60 Fenoxaprop-ethyl, on the other hand, was also previously described to be conjugated to GSH in black-grass, 61 late watergrass (Echinochloa phyllopogon) 62 and in monocotyledonous crops. 24 The degradation rates of the active metabolite fenoxaprop-acid were in all cases lower than for the prodrug fenoxaprop-ethyl. ...
BACKGROUND
Black‐grass (Alopecurus myosuroides Huds.) has become a problematic weed in cereals in Europe. Besides resistance to post‐emergent herbicides becoming increasingly widespread, enhanced metabolism of inhibitors of the synthesis of very‐long‐chain fatty acids (VLCFAs), such as flufenacet, is evolving. Yet, cross‐resistance patterns and evolution of this resistance remains poorly understood.
RESULTS
The cDNA sequences of five glutathione transferases (GSTs) upregulated in flufenacet resistant black‐grass were identified and used for recombinant protein expression. Moderate to slow detoxification of flufenacet was verified for all candidate GSTs expressed in E. coli, and the most active protein produced flufenacet‐alcohol instead of a glutathione conjugate, in the presence of reduced glutathione (GSH). Moreover, cross‐resistance to other VLCFA‐inhibitors e.g., acetochlor and pyroxasulfone and the ACCase inhibitor fenoxaprop was verified in vitro. Various other herbicides of different modes of action including VLCFA‐inhibitors were not detoxified by the candidate GSTs.
CONCLUSIONS
As several in planta upregulated GSTs detoxified flufenacet in vitro, the shift in sensitivity observed in black‐grass populations, is likely a result of an additive effect. The polygenic character and the relatively low turnover rate of the individual GSTs may explain the slow evolution of flufenacet resistance. In addition, flufenacet resistance was accompanied by cross‐resistance with some, but not all, herbicides of the same mode of action, and furthermore to the ACCase inhibitor fenoxaprop‐ethyl. Hence, not only the rotation of herbicide modes of action, but also of individual active ingredients is important for resistance management. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... Also, as various mutations in ACCase and/or ALS could confer resistance, it would be very costly and time consuming to develop methods and to identify each and every one of these mutations [20]. Furthermore, it could not be used to detect non-target site-based resistance, which had appeared to be a more dominant mechanism for resistance to ACCase and ALS inhibitors in grass weeds [53]. Novel techniques have emerged in herbicide resistance detection. ...
In this study, rapid resistance in-season quick (RISQ) tests were developed for detecting the resistance in Echinochloa spp. to penoxsulam, metamifop, and quinclorac, which are widely used in rice fields to control E. spp. biotypes. Seedlings in 1–2 leaf stages from nine biotypes of E. crusgalli, E. crusgalli var. zelayensis, and E. glabrescens, with different susceptibility to the three herbicides tested, were transplanted to plates containing nutrient agar and different rates of herbicides. The survival rates were recorded at 8 days after treatment when no more new roots emerged for all the treatments. By comparing the results from RISQ tests and whole-plant pot bioassays statistically, discrimination rates could be determined to distinguish resistant plants from susceptible plants. For penoxsulam, metamifop, and quinclorac, the discrimination rates were 0.3, 0.6, and 2.4 µmol/L, respectively. Two additional biotypes of E. crusgalli collected in rice fields were used to confirm the validation of the RISQ test and the obtained results by the RISQ test were consistent with that of the whole-plant pot bioassay. Therefore, the developed RISQ test would be a possible alternative method to determine the susceptibility of E. spp. to certain herbicides.
... Depending on the mutation, amino acid substitutions confer resistance to one or several of the three different classes of ACCase inhibitor herbicides, Ile1781Leu and Asp2078Gly being resistant to all three classes (Beckie and Tardif, 2012). In A. myosuroides, plants with the Trp2027Cys and Ile2041Asn mutations survive treatments with FOPs and DENs, while Gly2096 confers resistance exclusively to FOPs (Délye, 2005;Délye et al., 2008;Petit et al., 2010). The degree of cross-resistance provided by TSRs is thought to be one of the factors that determine the frequency at which they are found (Gaines et al., 2020;Powles and Yu, 2010). ...
Rapid adaptation of weeds to herbicide applications in agriculture through resistance development is a widespread phenomenon. In particular, the grass Alopecurus myosuroides is an extremely problematic weed in cereal crops with the potential to manifest resistance in only a few generations. Target‐site resistances (TSRs), with their strong phenotypic response, play an important role in this rapid adaptive response. Recently, using PacBio's long‐read amplicon sequencing technology in hundreds of individuals, we were able to decipher the genomic context in which TSR mutations occur. However, sequencing individual amplicons is costly and time consuming, thus impractical to implement for other resistance loci or applications. Alternatively, pool‐based approaches overcome these limitations and provide reliable allele frequencies, albeit at the expense of not preserving haplotype information. In this proof‐of‐concept study, we sequenced with PacBio High Fidelity (HiFi) reads long‐range amplicons (13.2 kb) encompassing the entire ACCase gene in pools of over hundred individuals, and resolved them into haplotypes using the clustering algorithm PacBio amplicon analysis (pbaa), a new application for pools in plants and other organisms. From these amplicon pools, we were able to recover most haplotypes from previously sequenced individuals of the same population. In addition, we analyzed new pools from a Germany‐wide collection of A. myosuroides populations and found that TSR mutations originating from soft sweeps of independent origin were common. Forward‐in‐time simulations indicate that TSR haplotypes will persist for decades even at relatively low frequencies and without selection, highlighting the importance of accurate measurement of TSR haplotype prevalence for weed management.
... In comparison to TSR, NTSR is more complex and frequently involves several enzyme superfamilies, such as cytochrome P450s (P450s), glucosyltransferases (GTs), glutathione S-transferases (GSTs), aldo-keto reductases, transporters and esterases [11][12][13]. Furthermore, TSR and NTSR can coevolve in response to herbicide selective pressure; hence, the two systems may coexist in the same species, population, or individual [14][15][16]. ...
Silene conoidea L. is an annual troublesome broadleaf weed in winter wheat fields in China. In recent years, field applications of tribenuron-methyl have been ineffective in controlling S. conoidea in Hebei Province, China. The aim of this study was to determine the molecular basis of tribenuron-methyl resistance in S. conoidea. Whole-plant response assays revealed that the resistant population (R) exhibited a higher level of resistance (382.3-fold) to tribenuron-methyl. The R population also showed high cross-resistance to other acetolactate synthase (ALS) inhibitors, including imazethapyr, bispyribac-sodium and florasulam. However, the R population could be controlled by the field-recommended rates of bentazone, MCPA, fluroxypyr, carfentrazone-ethyl and bromoxynil. In vitro ALS activity assays indicated that the tribenuron-methyl I50 value for the R population was 18.5 times higher than those for the susceptible population (S). ALS gene sequencing revealed an amino acid mutation, Trp-574-Leu, in the R population. Pretreatment with the P450 inhibitor malathion indicated that the R population might have cytochrome P450-mediated metabolic resistance. These results suggest that the Trp-574-Leu mutation and P450-mediated enhanced metabolism coexist in S. conoidea to generate tribenuron-methyl resistance. This is the first time that target-site and non-target-site resistance to tribenuron-methyl has been reported in S. conoidea.
... The cereal-safe FOP herbicide diclofop-methyl and clodinafop-propargyl were the most affected followed by the less metabolisable FOP herbicides haloxyfop-methyl fluazifop-butyl, and quizalofop-ethyl. On the other hand, clethodim and tepraloxydim were not impacted, similar to what has been observed so far for grass weed populations containing NTSR [21,57]. Pinoxaden, which is also cereal-safe, was partially affected, with 33% of wild-type WW2027-HGR plants surviving the treatment. ...
Herbicides that inhibit acetyl-CoA carboxylase (ACCase) are among the few remaining options for the post-emergence control of Lolium species in small grain cereal crops. Here, we determined the mechanism of resistance to ACCase herbicides in a Lolium multiflorum population (HGR) from France. A combined biological and molecular approach detected a novel W2027L ACCase mutation that affects aryloxyphenoxypropionate (FOP) but not cyclohexanedione (DIM) or phenylpyraxoline (DEN) subclasses of ACCase herbicides. Both the wild-type tryptophan and mutant leucine 2027-ACCase alleles could be positively detected in a single DNA-based-derived polymorphic amplified cleaved sequence (dPACS) assay that contained the targeted PCR product and a cocktail of two discriminating restriction enzymes. Additionally, we identified three well-characterised I1781L, I2041T, and D2078G ACCase target site resistance mutations as well as non-target site resistance in HGR. The non-target site component endowed high levels of resistance to FOP herbicides whilst partially impacting on the efficacy of pinoxaden and cycloxydim. This study adequately assessed the contribution of the W2027L mutation and non-target site mechanism in conferring resistance to ACCase herbicides in HGR. It also highlights the versatility and robustness of the dPACS method to simultaneously identify different resistance-causing alleles at a single ACCase codon.
... The cereal-safe FOP herbicide diclofop-methyl and clodinafop-propargyl were the most affected followed by the less metabolisable FOP herbicides haloxyfop-methyl uazifop-butyl, and quizalofop-ethyl. On the other hand, clethodim and tepraloxydim were not impacted, similar to what has been observed so far for grass weed populations containing NTSR [21,57]. Pinoxaden, which is also cereal-safe, was partially affected with 33% of wild type WW2027-HGR plants surviving the treatment. ...
Herbicides that inhibit acetyl-CoA carboxylase (ACCase) are among the few remaining options for the post-emergence control of Lolium species in small grain cereal crops. Here we have determined the mechanism of resistance to ACCase herbicides in a Lolium multiflorum population (HGR) from France. A combined biological and molecular approach detected a novel W2027L ACCase mutation that affects aryloxyphenoxypropionate (FOP) but not cyclohexanedione (DIM) or phenylpyraxoline (DEN) subclasses of ACCase herbicides. Both the wild type tryptophan and mutant leucine 2027-ACCase alleles could be positively detected in a single DNA-based derived Polymorphic amplified cleaved sequence (dPACS) assay that contained the targeted PCR product and a cocktail of two discriminating restriction enzymes. Additionally, we have identified three well-characterised I1781L, I2041T and D2078G target site resistance mutations as well as non-target site resistance in HGR. The non-target site component endowed high levels of resistance to FOP herbicides whilst partially impacting on the efficacy of pinoxaden and cycloxydim. This study adequately assessed the contribution of the W2027L mutation and non-target site mechanism in conferring resistance to ACCase herbicides in HGR. It also highlights the versatility and robustness of the dPACS method to simultaneously identify different resistance-causing alleles at a single ACCase codon.
... There are three distinct chemical families known to inhibit ACCase, namely aryloxyphenoxypropionate (APP), cyclohexanedione (CHD), and phenylpyrazolin (PPZ) (Hofer, Muehlebach, Hole, & Zoschke, 2006;Yu et al., 2007). Resistance alleles present in the newly identified donor plants contained a mutation at residue 2,027 of the ACCase protein, resulting in replacement of tryptophan by cysteine (Trp-2027-Cys) (Petit, Bay, Pernin, & Delye, 2010;Raghav, Singh, Chhokar, Sharma, & Kumar, 2016;Yu et al., 2007). Each of these mutations likely confers herbicide resistance by reducing the binding affinity of their respective target enzymes to the active ingredient, reducing their toxicity. ...
Acreage under grain sorghum [Sorghum bicolor (L.) Moench] in the United States has sharply declined over the past several decades. Among the major causes are the lack of better postemergence weed control options. Farmers opt for crops and tools that allow better management of weeds, and sorghum is not one of them. The discovery of sources of resistance to acetolactate synthase (ALS) and acetyl‐coenzyme A carboxylase (ACCase) inhibitor herbicides in feral relatives of sorghum opened a new horizon for development of a resistance‐based weed control option for the crop. The objective of this study is to demonstrate the agronomic potential of sorghum hybrids resistant to ALS and ACCase inhibitor herbicides and shed light on concerns that deployment of resistance traits may cause yield drags. A total of 186 hybrids involving homozygous ALS resistant, homozygous ACCase resistant, heterozygous ALS and ACCase resistance, and conventional hybrids plus commercial checks were grown in three sets consisting of 68, 62 and 56 entries for Set I, Set II, and Set III, respectively. The experiments were conducted during the 2014 and 2015 season in three replications at Kansas State University Agronomy Research Farm near Manhattan, KS. Data were collected on plant height, maturity, yield, and yield components, as well as grain nutritional traits. The analysis of the data revealed that the resistance technology has no negative effect on agronomic adaptability, yield potential, and nutritional traits of grain sorghum.
... To determine the importance of TSR mechanisms on the observed herbicide resistance phenotypes, we used the genotype sequencing (above) to calculate the proportion of individuals in each population which would be expected to survive each of the three tested herbicides, based on presence of TSR mutations alone. Whilst different ALS and ACCase mutations in A. myosuroides may vary in their protective efficacy, previously published information, e.g., 20,[57][58][59] suggests that they can be considered dominant in conveying survival at field-relevant herbicide doses. Using this information, the proportion of individuals carrying TSR resistance to each herbicide was calculated, hereafter referred to as the ALS, Fop and Dim TSR frequencies. ...
Intense selection by pesticides and antibiotics has resulted in a global epidemic of evolved resistance. In agriculture and medicine, using mixtures of compounds from different classes is widely accepted as optimal resistance management. However, this strategy may promote the evolution of more generalist resistance mechanisms. Here we test this hypothesis at a national scale in an economically important agricultural weed: blackgrass (Alopecurus myosuroides), for which herbicide resistance is a major economic issue. Our results reveal that greater use of herbicide mixtures is associated with lower levels of specialist resistance mechanisms, but higher levels of a generalist mechanism implicated in enhanced metabolism of herbicides with diverse modes of action. Our results indicate a potential evolutionary trade-off in resistance management, whereby attempts to reduce selection for specialist resistance traits may promote the evolution of generalist resistance. We contend that where specialist and generalist resistance mechanisms co-occur, similar trade-offs will be evident, calling into question the ubiquity of resistance management based on mixtures and combination therapies.
... L'usage systématique et unique d'un seul type d'herbicides est connu pour être depuis 30 ans à l'origine de la sélection rapide de résistants à travers le monde (Vacher et al., 2003;Moss, 2006). De nouveaux herbicides, comme le pinoxa-den, inhibiteur de l'ACCase appartenant à une nouvelle famille chimique (phénylpyrazolines), ne peuvent pas prétendre être une solution à la résistance (Moss, 2006;Petit et al., 2010). En effet, de nouvelles solutions, dont l'introduction de nouveaux modes d'action, particulièrement le prosulfocarbe, ont été développées pour la bonne gestion intégrée des adventices résistantes (Swanton et Weise, 1991;Buhler et al., 2000). ...
Abstract
Ryegrass (Lolium rigidum Gaud.) developed resistance to Acetolactate Synthase (ALS) and Acetyl-CoA Carboxylase (ACCase)
inhibiting herbicides. The objective is to evaluate the effect of the active substance ‘Prosulfocarb’, sprayed in post-sowing preemergence at different rates and associated with S-metolachlor on ryegrass resistant to registered rate (3200 g ha-1) and according to the
stages of application (SAP1: 1 day after sowing of wheat, SAP2: 7 days after sowing and SAP3: 2 to 3 leaves after emergence).
The study also evaluated the effect of Prosulfocarb and post-emergence herbicides on durum wheat yield and its components. To
meet these objectives, field trials were carried out in northern Tunisia (Mateur/Bizerte), with a Randomized Complete Bloc Design
(RCBD). The evaluation was carried out over three successive seasons (2012/13 to 2014/15). The results revealed that the efficacy
of prosulfocarb improved with increasing application rate. The S-metolachlor favored the improvement of prosulfocarb efficacy
by 6 to 15%. Results also showed that the efficacy of prosulfocarb was better in the first two growth stages of the application
(SAP1 and SAP2) and low when applied after emergence (SAP3). Prosulfocarb allowed a gain of 7.3% of durum wheat yield. The
ryegrass infestation (92.5 plants/m²) affected the number of grains per spike and caused durum wheat yield losses of up to 39%.
... These mechanisms selected by ACCase inhibitors can confer cross-resistance to pinoxaden. For instance, resistance selected by the fenoxaprop ACCase inhibiting herbicide conferred crossresistance to pinoxaden (Yu et al., 2007;Petit et al., 2010). However, the low frequency of resistance to pinoxaden solely (one population) suggests that resistance to pinoxaden may be the result of cross-resistance selected by other ACCase inhibiting herbicides or other modes of action used in the past. ...
A survey of the prevalence of rigid ryegrass ( Lolium rigidum ) resistant to ACCase and ALS herbicides was conducted in major-cereal growing regions in the north of Tunisia. Randomly collected ryegrass populations were assessed, using the Syngenta RISQ ® test, for resistance to clodinafop-propargyl, iodosulphuron + mesosulphuron and pinoxaden. Of the 177 tested populations, 58% exhibited resistance to clodinafop-propargyl and 52% to iodosulphuron + mesosulphuron, with 40% exhibiting resistance to both herbicides. Significant variations in the frequencies of rigid ryegrass resistant to clodinafop-propargyl and/or iodosulphuron + mesosulphuron were observed between surveyed regions which may be the result of differences in the history of herbicide use. Over 50% of resistant populations contained 60% of resistant plants or more, indicating the extent of resistance evolution in these regions. Our study demonstrates that the extent of resistance to ACCase and ALS-inhibiting herbicides in rigid ryegrass is widespread in major cereal-growing regions of Tunisia. Therefore, weed management must be focused on reducing the frequency of herbicide application, using multiple herbicide mechanisms of action, rotating different modes of action and integrating alternative control options.
... These herbicides inhibit plastidic ACCase enzyme, a key enzyme for fatty acid synthesis in all plants. However, their repeated and extensive use for many years has led to the evolution of herbicide resistant populations in many important grass weed species such as black grass (Alopecurus myosuroides) (Délye et al., 2005;Petit et al., 2010), wild oat (Avena fatua) (Cruz-Hipolito et al., 2011), sterile oat (Avena sterilis) (Papapanagiotou et al., 2012(Papapanagiotou et al., , 2015 and L. rigidum (Scarabel et al., 2011). Until now there have been reported 48 grass weed species with resistance to these herbicides (Heap, 2019). ...
Three putative resistant (R1, R2, R3) and one susceptible (S) Lolium rigidum populations originating from Greece were studied for resistance to ALS and ACCase inhibiting herbicides, using whole plant, sequencing of als and accase gene, and in vitro ALS activity assays. The S and two R (R1, R2) populations were also evaluated for fitness in competition with wheat. The whole plant assay indicated unsatisfactory control of the R populations with mesosulfuron-methyl + iodosulfuron-methyl or pinoxaden application, whereas sequencing of the als gene revealed that all ALS-resistant individuals had a Pro-197 substitution by Leu, Glu, Ser, Ala, Thr, or Gln. In addition, the accase gene of all pinoxaden resistant individuals had an Ile-2041 substitution by Asn or Thr. Furthermore, sequencing of the individuals surviving mesosulfuron-methyl + iodosulfuron-methyl or pinoxaden treatment revealed co-existence of point mutations in the accase or als genes, respectively, demonstrating multiple resistance. The in vitro activity of the ALS enzyme confirmed that resistance to mesosulfuron-methyl + iodosulfuron-methyl was due altered target-site. The recorded higher vigor and greater competitive ability of S population against wheat as compared with that of the R populations suggests an associated fitness cost with multiple resistance.
... These herbicides, which inactivate ACCase, block fatty acid biosynthesis and reduce the production of phospholipids are major constituents of cell membranes [8]. APP and CHD herbicides have been used to control weeds since they were introduced in the 1970s and 1980s, respectively [9]. Furthermore, pinoxaden, which belongs to the PPZ group, was introduced in 2006 to control grass weeds during wheat cultivation [10]. ...
The weed Phalaris brachystachys Link. severely affects winter cereal production. Acetyle-CoA Carboxylase (ACCase)-inhibiting herbicides are commonly used to control this weed in wheat fields. Thirty-six populations with suspected resistance to ACCase-inhibiting herbicides were collected from wheat fields in the Golestan Province in Iran. A rapid test performed in Petri dishes and whole-plant dose–response experiments were conducted to confirm and investigate the resistance level of P. brachystachys to ACCase-inhibiting herbicides. The seed bioassay results showed that 0.02 mg ai L⁻¹ clodinafop-propargyl (CP) and 1.36 mg ai L⁻¹ of the diclofop-methyl (DM) solution were the optimal amounts for reliably screening resistant and susceptible P. brachystachys populations. In the whole plant bioassay, all populations were found to be resistant to CP, resistance ratios ranging from 2.7 to 11.6, and all of the CP-resistant populations exhibited resistance to DM. Fourteen populations showed low resistance to cycloxydim, and thirteen of these populations were also 2-fold resistant to pinoxaden. The results showed that DM resistance in some P. brachystachys populations is likely due to their enhanced herbicide metabolism, which involves Cytochrome P450 monooxygenases, as demonstrated by the indirect assay. This is the first report confirming the cross-resistance of ACCase-inhibiting herbicides in P. brachystachys in Iran.
... NTSR is hard to manage because weeds have unpredictable resistance to herbicides with different chemical structures and/or target proteins (Délye, 2013). Furthermore, recent studies have demonstrated that weeds with NTSR can transmit cross-resistance to other herbicides with different modes of action, even to those not yet marketed (Petit et al., 2010). This is because NTSR is much more of a general adaptive response to herbicides (Yuan et al., 2007). ...
We report the first plastome sequence of giant ragweed (Ambrosia trifida); with this new genome information, we assessed the phylogeny of Asteraceae and the transcriptional profiling against glyphosate resistance in giant ragweed. Assembly and genic features show a normal angiosperm quadripartite plastome structure with no signatures of deviation in gene directionality. Comparative analysis revealed large inversions across the plastome of giant ragweed and the previously sequenced members of the plant family. Asteraceae plastid genomes contain two inversions of 22.8 and 3.3 kb; the former is located between trnS-GCU and trnG-UCC genes, and the latter between trnE-UUC and trnT-GGU genes. The plastid genome sequences of A. trifida and the related species, Ambrosia artemisiifolia, are identical in gene content and arrangement, but they differ in length. The phylogeny is well-resolved and congruent with previous hypotheses about the phylogenetic relationship of Asteraceae. Transcriptomic analysis revealed divergence in the relative expressions at the exonic and intronic levels, providing hints toward the ecological adaptation of the genus. Giant ragweed shows various levels of glyphosate resistance, with introns displaying higher expression patterns at resistant time points after the assumed herbicide treatment.
... In recent past, herbicide resistance has emerged as the greatest concern of contemporary agriculture which relies primarily on synthetic inputs for its sustainability (Petit et al., 2010). Littleseed canarygrass (Phalaris minor Retz.), the most troublesome weed of wheat crop has developed resistance against isoproturon in North-Western Indo-Gangetic plains of India. ...
Widespread resistance in Phalaris minor is a major challenge for sustainable productivity.
Recent increases in the development of herbicide resistance in Phalaris minor worldwide
demand a high up strategies to control this weed. Herbicide-resistant weeds are a
constraint to weed management. The use of potential management strategies is crucial in
assuring sustainable production. A pot-culture experiment was conducted during the winter
season of 2017-18 with the objective to evaluate the herbicidal efficacy for management of
isoproturon-resistant Phalaris minor. Post-emergence herbicides used in this study were
clodinafop –propargyl, metribuzin, sulfosulfuron, pinoxaden and Halauxifen methyl
+Pyroxsulam. Increased doses (up to 1.5X &2.0X) of herbicide provided effective control
of P. minor. However, application of recommended dose (1.0X) of metribuzin provides a
satisfactory control of P. minor. These findings suggest that post-emergence herbicide
controls resistant P. minor and delay further herbicide resistance in this weed.
The selective chemical control of wild grasses in wheat is primarily determined by the relative rates of herbicide metabolism, with the superfamily of cytochromes P450 (CYPs) playing a major role in catalyzing phase 1 detoxification reactions. This selectivity is enhanced by herbicide safeners, which induce CYP expression in cereals, or challenged by the evolution of nontarget site resistance (NTSR) in weeds such as blackgrass. Using transcriptomics, proteomics, and functional expression in recombinant yeast, CYPs linked to safener treatment and NTSR have been characterized in wheat and blackgrass. Safener treatment resulted in the induction of 13 families of CYPs in wheat and 5 in blackgrass, with CYP71, CYP72, CYP76, and CYP81 members active toward selective herbicides in the crop. Based on their expression and functional activities, three inducible TaCYP81s were shown to have major roles in safening in wheat. In contrast, a single AmCYP81 that was enhanced by NTSR, but not by safening, was found to dominate herbicide detoxification in blackgrass.
Herbicides have been placed in global Herbicide Resistance Action Committee (HRAC) herbicide groups based on their sites of action (e.g., acetolactate synthase–inhibiting herbicides are grouped in HRAC Group 2). A major driving force for this classification system is that growers have been encouraged to rotate or mix herbicides from different HRAC groups to delay the evolution of herbicide-resistant weeds, because in theory, all active ingredients within a herbicide group physiologically affect weeds similarly. Although herbicide resistance in weeds has been studied for decades, recent research on the biochemical and molecular basis for resistance has demonstrated that patterns of cross-resistance are usually quite complicated and much more complex than merely stating, for example, a certain weed population is Group 2-resistant. The objective of this review article is to highlight and describe the intricacies associated with the magnitude of herbicide resistance and cross-resistance patterns that have resulted from myriad target-site and non–target site resistance mechanisms in weeds, as well as environmental and application timing influences. Our hope is this review will provide opportunities for students, growers, agronomists, ag retailers, regulatory personnel, and research scientists to better understand and realize that herbicide resistance in weeds is far more complicated than previously considered when based solely on HRAC groups. Furthermore, a comprehensive understanding of cross-resistance patterns among weed species and populations may assist in managing herbicide-resistant biotypes in the short term by providing growers with previously unconsidered effective control options. This knowledge may also inform agrochemical company efforts aimed at developing new resistance-breaking chemistries and herbicide mixtures. However, in the long term, nonchemical management strategies, including cultural, mechanical, and biological weed management tactics, must also be implemented to prevent or delay increasingly problematic issues with weed resistance to current and future herbicides.
Weeds in agricultural settings continually adapt to stresses from ecological and anthropogenic sources, in some cases leading to resistant populations. However, consequences of repeated sub‐lethal exposure of these stressors on fitness and stress “memory” over generations remain poorly understood. We measured plant performance over a transgenerational experiment with Arabidopsis thaliana where plants were exposed to sub‐lethal stress induced by the herbicides glyphosate or trifloxysulfuron, stresses from clipping or shading in either one (G1) or four successive generations (G1–G4), and control plants that never received stress. We found that fourth‐generation (G4) plants that had been subjected to three generations of glyphosate or trifloxysulfuron stress produced higher post‐stress biomass, seed weight, and rosette area as compared to that produced by plants that experienced stress only in the first generation (G1). By the same measure, clipping and shade were more influential on floral development time (shade) and seed weight (clipping) but did not show responsive phenotypes for vegetative metrics after multiple generations. Overall, we found that plants exhibited more rapid transgenerational vegetative “stress memory” to herbicides while reproductive plasticity was stressor dependent and similar between clipping/shade and anthropogenic stressors. Our study suggests that maternal plant stress memory aids next‐generation plants to respond and survive better under the same stressors.
Recently, the herbicide fomesafen has frequently failed to control the troublesome weed Ipomoea nil in soybean fields in Liaoning Province, China. Hence, we collected 10 suspected resistant populations and evaluated their sensitivity to fomesafen. The results revealed various degrees of Ipomoea nil resistance to fomesafen, with a resistance index of 2.88 to 22.43; the highest value occurred in the LN3 population. Therefore, the mechanisms of the resistance in LN3 to fomesafen were explored. After fomesafen treatment, the expression levels of InPPX1 and InPPX2 genes were 4.19- and 9.29-fold higher, respectively, in LN3 than those in the susceptible (LN1) population. However, mutations and copy number variations were not detected between the two populations. Additionally, malathion pretreatment reduced the dose necessary to halve the growth rate of LN3 by 58%. Liquid chromatography with tandem mass spectrometry demonstrated that metabolism of fomesafen was significantly suppressed by malathion. Moreover, LN3 displayed increased reactive oxygen species scavenging capacity, which was represented by higher superoxide dismutase and peroxidase activities after fomesafen application than those in LN1. An orthogonal partial least squares-discriminant analysis revealed that the high resistance in LN3 could be attributed mainly to enhanced metabolism. Fortunately, the fomesafen-resistant I. nil remained sensitive to 2,4-D-ethylhexylester and bentazon, providing methods for its control.
Black-grass (Alopecurus myosuroides Huds.) is a common weed in Chinese wheat fields, and has become troublesome due to its evolution of herbicide resistance. One black-grass population (HN-14) collected from a wheat field where herbicides were applied was suspected to be resistant (R) to mesosulfuron-methyl. This study aims to establish a cross-resistance pattern and explore potential resistance mechanisms. The results of a whole-plant dose response assay showed that the resistant (R) population had a high of resistance to mesosulfuron-methyl (33-fold); meanwhile, no synergism of P450s activity inhibitor malathion was observed. The sequencing results revealed that ALS resistance mutation Trp-574-Leu occurred in R plants. The results of in vitro ALS enzyme activity assays also supported that the extractable ALS from R plants were 23.22-fold resistant to mesosulfuron-methyl. In the light of the “R” resistance rating system, HN-14 has evolved RRR and RR resistance to fenoxaprop-P-ethyl, clodinafop-propargyl, haloxyfop-methyl, and fluazifop-P-butyl and R? (resistance may be developing) to pinoxaden, however remains sensitive to imazethapyr, quizalofop-P-ethyl, tralkoxydim, and isoproturon. These results indicated that the mesosulfuron-methyl resistance in the black-grass population HN-14 was driven by a target-site mechanism rather than a nontarget (at least P450s-mediated) mechanism.
Research was conducted using a functional malachite green colorimetric assay to evaluate acetyl-coenzyme A carboxylase (ACCase) activity previously identified as resistant to sethoxydim and select aryloxyphenoxypropionate (FOPs) herbicides, fenoxaprop, and fluazifop. Two resistant southern crabgrass [ Digitaria ciliaris (Retz.) Koeler] biotypes, R1 and R2, containing an Ile-1781-Leu amino acid substitution and previously identified as resistant to sethoxydim, pinoxaden, and fluazifop but not clethodim was utilized as the resistant chloroplastic ACCase source compared with known susceptible (S) ACCase. Dose-response studies with sethoxydim, clethodim, fluazifop- p -butyl, and pinoxaden (0.6 to 40 µM) were conducted to compare the ACCase–herbicide interactions of R1, R2, and S using the malachite green functional assay. Assay results indicated that R biotypes required more ACCase-targeting herbicides to inhibit ACCase activity compared with S. IC 50 values of all four herbicides for R biotypes were consistently an order of magnitude greater than those of S. No sequencing differences in the carboxyltransferase domain was observed for R1 and R2; however, R2 IC 50 values were greater across all herbicides. These results indicate the malachite green functional assay is effective in evaluating ACCase activity of R and S biotypes in the presence of ACCase-targeting herbicides, which can be used as a replacement for the ¹⁴ C-based radiometric functional assays.
Rice is one of the most important food crops in the world. Weeds seriously affect the rice yield and grain quality. In recent years, there are tremendous progresses in the research and application of herbicide-resistant genes in rice worldwide. This article reviews the working mechanisms of six herbicides (glyphosate, glufosinate, acetolactate synthase inhibitor herbicides, acetyl-CoA carboxylase inhibitor herbicides, hydroxyhenylpyruvate dioxygenase (HPPD) inhibitor herbicides and dinitroaniline herbicides), the resistance mutations of the corresponding herbicide-target genes, and the herbicide detoxification mechanisms by non-target genes. Examples are provided on herbicide-resistant rice materials obtained by transformation of exogenous resistance genes, by artificial mutagenesis and mutant screening, and by modifying the target genes through gene editing. This paper also introduces the current application of herbicide-resistant rice, points out problems that may be caused by utilization of herbicide resistant rice and solutions to the problems, and discusses the future prospects for the development of herbicide-resistant rice.
Capsella bursa-pastoris (L.) Medik. has evolved resistance to ALS-inhibiting herbicides on a large scale. Previous studies primarily focused on the target-site resistance (TSR), and the non-TSR (NTSR) is not well characterized. In this study, pre-treatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion clearly reduced the tribenuron-methyl resistance in the resistant (R) population. After tribenuron-methyl treatment, the glutathione S-transferase (GST) activity of R plants was significantly higher than that of susceptible (S) plants. The higher tribenuron-methyl metabolism in R plants was also confirmed by using LC-MS/MS analysis. Isoform sequencing (Iso-Seq) combined with RNA sequencing (RNA-Seq) was used to identify candidate genes involved in non-target metabolic resistance in this population. A total of 37 differentially expressed genes were identified, 11 of them constitutively upregulated in R plants, including three P450s, one GST, two glycosyltransferases, two ATP-binding cassette transporters, one oxidase, and two peroxidases. This study confirmed the metabolic tribenuron-methyl resistance in C. bursa-pastoris, and the transcriptome data obtained by Iso-Seq combined with RNA-Seq provide gene resources for understanding the molecular mechanism of NTSR in C. bursa-pastoris.
The occurrence of multiple herbicide resistant weeds has increased considerably in glyphosate-resistant soybean fields in Brazil; however, the mechanisms governing this resistance have not been studied. In this study, the target-site and nontarget-site mechanisms were characterized in an Eleusine indica population (R-15) with multiple resistance to the acetyl-CoA carboxylase (ACCase) inhibitors, glyphosate, imazamox and paraquat. Absorption and translocation rates of 14C-diclofop-methyl, 14C-imazamox and 14C-glyphosate of the R-15 population were similar to those of a susceptible (S-15) population; however, the R-15 population translocated ~38% less 14C-paraquat to the rest of plant and roots than the S-15 population. Furthermore, the R-15 plants metabolized (by P450 cytochrome) 55 and 88% more diclofop-methyl (conjugate) and imazamox (imazamox-OH and conjugate), respectively, than the S-15 plants. In addition, the Pro-106-Ser mutation was found in the EPSPS gene of this population. This report describes the first characterization of the resistance mechanisms in a multiple herbicide resistant weed from Brazil.
Fenoxaprop-P-ethyl is widely used to control the Italian ryegrass (Lolium multiflorum Lam.) in China. Recently, Italian ryegrass populations have been reported with resistance to fenoxaprop-P-ethyl in two provinces (Jiangsu and Henan) of China. It was important to clarify the resistance patterns of these populations which had evolved resistance to fenoxaprop-P-ethyl. In this study, we investigated three Italian ryegrass populations (HZGX-2, HZYC-4, and HZYC-5) that were involved with high resistance to fenoxaprop-P-ethyl. The HZGX-2 population showed low cross-resistance to clethodim, haloxyfop-R-methyl, clodinafop-propargyl, and quizalofop-P-ethyl, but was still susceptible to sethoxydim and pinoxaden. The HZYC-4 and HZYC-5 populations showed cross resistance to all tested acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides. We examined the genetic changes in three Italian ryegrass populations and identified four mutations, named D2078G, C2088R, I1781L, and I2041N and occurring within different frequencies in these populations. These mutations have been reported to underlie resistance to ACCase-inhibiting herbicides. In the HZGX-2 population wild type frequency was 73%, and the mutation frequencies at positions 1781, 2041, and 2078 were 13%, 7%, and 7%, respectively. In the HZYC-4 population, the mutation frequencies were 93% at 1781 and 7% at 2041. In the HZYC-5 population, the mutation frequencies were 72% at 1781, 16% at 2041, and 12% at 2088. There was no wild type found in the HZYC-4 and HZYC-5 populations, either. The cytochrome P450 inhibitors was shown to slightly reduce the ED50 values of fenoxaprop-P-ethyl-resistant populations, which implied a combination of target-site resistance and non-target-site resistance was involved in resistance. This study can help the weed management of agricultural activities in China and other countries.
In Argentina, Lolium spp. occurs in 40% of winter cereal crops from the Pampas. Several years ago, cases of glyphosate resistant perennial ryegrass ( Lolium perenne L.) were detected and in order to kill these plants, the use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides has been considered. The aim of this study was to evaluate the sensitivity of a putative pinoxaden-resistant L. perenne population to ACCase inhibitor herbicides. Around 80% of plants from the putative resistant population survived at a recommended dose of pinoxaden, and they produced viable seeds. The resistance indices (RIs) to pinoxaden were 5.1 and 2.8 for plant survival and seed production, respectively. A single-point mutation which conferred a D2078G substitution in ACCase was the source of the resistance. In order to match the plant control achieved in the susceptible population, the resistant population required 5.4- and 10.4-fold greater doses of clethodim and quizalofop, respectively. RIs for viable seed production when treated with clethodim and quizalofop were 3.3 and 6.6, respectively. The D2078G mutation endowed significant levels of resistance to pinoxaden, clethodim and quizalofop. For three herbicides, the level of resistance of a pinoxaden-resistant L. perenne population to ACCase inhibitors was evaluated, based on an evaluation of dose-response for plant survival and seed production. The RIs were higher for plant survival than for seed production. In Argentina, the selection pressure associated with clethodim and haloxifop preplant application, and pinoxaden use on wheat and barley crops, would have favoured the propagation of the D2078G mutation with its associated resistance.
Bearded sprangletop [ Diplachne fusca (L.) P. Beauv. ex Roem. & Schult. ssp. fascicularis (Lam.) P. M. Peterson & N. Snow] is a noxious annual grass weed of paddy fields, distributed in coastal regions of the Jiangsu and Hebei provinces in China. Cyhalofop-butyl has been widely used to control grass weeds since 2006 in China. Overreliance on cyhalofop-butyl has led to the evolution of resistant weeds. In this study, the resistance level and cyhalofop-butyl resistance mechanisms were investigated in the putative resistant (JSHH) population. The dose–response experiments showed that the JSHH D . fusca population had evolved 8.9-fold resistance to cyhalofop-butyl. Acetyl-CoA carboxylase (ACCase) sequencing revealed a point mutation (GGC to GCC) at amino acid position 2096, resulting in a Gly-2096-Ala substitution in the resistant population. To our knowledge, this is the first case of cyhalofop-butyl resistance in D . fusca and the first report of a target-site mutation conferring resistance to ACCase-inhibiting herbicides in D . fusca . In addition, the resistant D . fusca population (JSHH) with the Gly-2096-Ala mutation was cross-resistant to the aryloxyphenoxypropionate herbicide metamifop, the cyclohexanedione herbicide sethoxydim, and the phenylpyrazolin herbicide pinoxaden.
A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
Acetyl-coenzyme A carboxylase (ACCase) assays and absorption, translocation, and metabolism experiments were conducted to investigate the mechanism(s) responsible for resistance in a johnsongrass biotype that exhibited low levels of resistance to the cyclohexanedione (CHD) herbicide sethoxydim and the aryloxyphenoxypropionate (APP) herbicides quizalofop-P and fluazifop-P. The rate of [14C]quizalofop-ethyl absorption was significantly higher in the resistant compared to the susceptible biotype 8, 24, and 48 h after treatment (HAT), but by 72 HAT, there was no significant difference in the amount of [14C]quizalofop-ethyl detected in either biotype. Additionally, little or no differences in the translocation of [14C]quizalofop-ethyl were observed in the resistant and susceptible biotypes at any time interval after application. In [14C]quizalofop-ethyl metabolism experiments, similar levels of quizalofop-ethyl and quizalofop metabolites were observed in the resistant and susceptible biotypes 8, 24, 48, and 72 HAT, but slightly higher levels of quizalofop acid were detected in the resistant biotype 48 and 72 HAT. In ACCase assays, the concentrations of quizalofop-P, clethodim, and sethoxydim that inhibited ACCase activity by 50% (I50) were statistically similar in the two biotypes, indicating that the resistant johnsongrass biotype contains an ACCase that is sensitive to the APP and CHD herbicides. In the absence of APP or CHD herbicides, however, the specific activity of ACCase in the resistant biorype was two to three times greater than that of the susceptible biotype. The specific activity of ACCase in the resistant biotype was also significantly greater than that of the susceptible biotype in the presence of all concentrations of quizalofop-P and sethoxydim and in the presence of 0.1, 1, and 10 μ.M clethodim. These results suggest that resistance to quizalofop-P and sethoxydim is conferred by an overproduction of ACCase in the resistant johnsongrass biotype.
Diclofop-resistant Italian ryegrass is a major weed problem in wheat production. This study aimed to determine the resistance pattern of diclofop-resistant Italian ryegrass accessions from the southern United States to the latest commercialized herbicides for wheat production, pinoxaden and mesosulfuron, and to other acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors. Twenty-nine of 36 accessions were resistant to the commercial dose of diclofop. The majority (80%) of diclofop-resistant accessions were also resistant to clodinafop. Of 25 diclofop-resistant accessions, 5 were resistant to pinoxaden. All accessions tested were susceptible to the commercial dose of clethodim and sethoxydim. The cross-resistance pattern of diclofop-resistant Italian ryegrass to other ACCase inhibitors was 20% for pinoxaden and none with clethodim or sethoxydim. One accession was resistant to mesosulfuron but not to diclofop. This mesosulfuron-resistant accession was cross-resistant to sulfometuron but not to imazamox. All diclofop-resistant accessions tested were susceptible to ALS inhibitors, mesosulfuron, sulfometuron, and imazamox. Therefore, diclofop-resistant Italian ryegrass in Arkansas can be controlled with imazamox (in Clearfield wheat) and can mostly be controlled with mesosulfuron and pinoxaden. It could also be controlled by other selective grass herbicides in broadleaf crops. Nomenclature: Clethodim; clodinafop; diclofop; imazamox; mesosulfuron; pinoxaden; sethoxydim; sulfometuron; Italian ryegrass, Lolium multiflorum Lam., wheat, Triticum aestivum L.
Understanding pesticide metabolism in plants and microorganisms is necessary for pesticide development, for safe and efficient use, as well as for developing pesticide bioremediation strategies for contaminated soil and water. Pesticide biotransforma- tion may occur via multistep processes known as metabolism or cometabolism. Co- metabolism is the biotransformation of an organic compound that is not used as an energy source or as a constitutive element of the organism. Individual reactions of degradation-detoxification pathways include oxidation, reduction, hydrolysis, and conjugation. Metabolic pathway diversity depends on the chemical structure of the xenobiotic compound, the organism, environmental conditions, metabolic factors, and the regulating expression of these biochemical pathways. Knowledge of these enzymatic processes, especially concepts related to pesticide mechanism of action, resistance, selectivity, tolerance, and environmental fate, has advanced our under- standing of pesticide science, and of plant and microbial biochemistry and physi- ology. There are some fundamental similarities and differences between plant and microbial pesticide metabolism. In this review, directed to researchers in weed sci- ence, we present concepts that were discussed at a symposium of the American Chemical Society (ACS) in 1999 and in the subsequent book Pesticide Biotransfor- mation in Plants and Microorganism: Similarities and Divergences, edited by J. C. Hall, R. E. Hoagland, and R. M. Zablotowicz, and published by Oxford University Press, 2001. Nomenclature: American Chemical Society; fenchlorazole-ethyl; glutathione; glu- tathione-S-transferase; naphthalic anhydride; polyaromatic hydrocarbons; polychlor- inated biphenyls; reductive dehalogenation; trichloroethylene.
In 2005, a random survey was conducted across 14 million hectares of the Western Australian grain belt to establish the frequency and distribution of herbicide-resistant wild oat (Avena spp.) in cropping fields. In total, 677 cropping fields were visited, with wild oat populations collected from 150 fields. These wild oat populations were screened with several herbicides commonly used to control this weed. Most of the wild oat populations (71%) were found to contain individuals resistant to the ACCase-inhibiting herbicide diclofop-methyl. Resistance to other ACCase-inhibiting herbicides was markedly lower. Herbicides of alternative modes of action were effective on all wild oat populations. Overall, wild oat resistance to diclofop-methyl was found to be widespread across the Western Australian grain belt, but resistance to other herbicides was relatively low. Therefore, through diversity in herbicide use and with cultural management, it is possible to maintain wild oat populations at a low level and/or minimise herbicide resistance evolution.
A 3,300-bp DNA fragment encoding the carboxyl-transferase domain of the multidomain, chloroplastic acetyl-coenzyme A carboxylase (ACCase) was sequenced in aryloxyphenoxypropionate (APP)-resistant and -sensitive Alopecurus myosuroides (Huds.). No resistant plant contained an Ile-1,781-Leu substitution, previously shown to confer resistance to APPs and cyclohexanediones (CHDs). Instead, an Ile-2,041-Asn substitution was found in resistant plants. Phylogenetic analysis of the sequences revealed that Asn-2,041 ACCase alleles derived from several distinct origins. Allele-specific polymerase chain reaction associated the presence of Asn-2,041 with seedling resistance to APPs but not to CHDs. ACCase enzyme assays confirmed that Asn-2,041 ACCase activity was moderately resistant to CHDs but highly resistant to APPs. Thus, the Ile-2,041-Asn substitution, which is located outside a domain previously shown to control sensitivity to APPs and CHDs in wheat (Triticum aestivum), is a direct cause of resistance to APPs only. In known multidomain ACCases, the position corresponding to the Ile/Asn-2,041 residue in A. myosuroides is occupied by an Ile or a Val residue. In Lolium rigidum (Gaud.), we found Ile-Asn and Ile-Val substitutions. The Ile-Val change did not confer resistance to the APP clodinafop, whereas the Ile-Asn change did. The position and the particular substitution at this position are of importance for sensitivity to APPs.
In grasses, residues homologous to residues Ile-1,781 and Ile-2,041 in the carboxyl-transferase (CT) domain of the chloroplastic acetyl-coenzyme A (CoA) carboxylase (ACCase) from the grass weed black-grass (Alopecurus myosuroides [Huds.]) are critical determinants for sensitivity to two classes of ACCase inhibitors, aryloxyphenoxypropionates (APPs) and cyclohexanediones. Using natural mutants of black-grass, we demonstrated through a molecular, biological, and biochemical approach that residues Trp-2,027, Asp-2,078, and Gly-2,096 are also involved in sensitivity to ACCase inhibitors. In addition, residues Trp-2,027 and Asp-2,078 are very likely involved in CT activity. Using three-dimensional modeling, we found that the side chains of the five residues are adjacent, located at the surface of the inside of the cavity of the CT active site, in the vicinity of the binding site for APPs. Residues 1,781 and 2,078 are involved in sensitivity to both APPs and cyclohexanediones, whereas residues 2,027, 2,041, and 2,096 are involved in sensitivity to APPs only. This suggests that the binding sites for these two classes of compounds are overlapping, although distinct. Comparison of three-dimensional models for black-grass wild-type and mutant CTs and for CTs from organisms with contrasted sensitivity to ACCase inhibitors suggested that inhibitors fitting into the cavity of the CT active site of the chloroplastic ACCase from grasses to reach their active sites may be tight. The three-dimensional shape of this cavity is thus likely of high importance for the efficacy of ACCase inhibitors.
Grass weed populations resistant to aryloxyphenoxypropionate (APP) and cyclohexanedione herbicides that inhibit acetyl-CoA carboxylase (ACCase; EC 6.4.1.2) represent a major problem for sustainable agriculture. We investigated the molecular basis of resistance to ACCase-inhibiting herbicides for nine wild oat (Avena sterilis ssp. ludoviciana Durieu) populations from the northern grain-growing region of Australia. Five amino acid substitutions in plastid ACCase were correlated with herbicide resistance: Ile-1,781-Leu, Trp-1,999-Cys, Trp-2,027-Cys, Ile-2,041-Asn, and Asp-2,078-Gly (numbered according to the Alopecurus myosuroides plastid ACCase). An allele-specific PCR test was designed to determine the prevalence of these five mutations in wild oat populations suspected of harboring ACCase-related resistance with the result that, in most but not all cases, plant resistance was correlated with one (and only one) of the five mutations. We then showed, using a yeast gene-replacement system, that these single-site mutations also confer herbicide resistance to wheat plastid ACCase: Ile-1,781-Leu and Asp-2,078-Gly confer resistance to APPs and cyclohexanediones, Trp-2,027-Cys and Ile-2,041-Asn confer resistance to APPs, and Trp-1,999-Cys confers resistance only to fenoxaprop. These mutations are very likely to confer resistance to any grass weed species under selection imposed by the extensive agricultural use of the herbicides.
The acetyl-coenzyme A carboxylase (ACCase)-inhibiting cyclohexanedione herbicide clethodim is used to control grass weeds infesting dicot crops. In Australia clethodim is widely used to control the weed Lolium rigidum. However, clethodim-resistant Lolium populations have appeared over the last 5 years and now are present in many populations across the western Australian wheat (Triticum aestivum) belt. An aspartate-2078-glycine (Gly) mutation in the plastidic ACCase enzyme has been identified as the only known mutation endowing clethodim resistance. Here, with 14 clethodim-resistant Lolium populations we revealed diversity and complexity in the molecular basis of resistance to ACCase-inhibiting herbicides (clethodim in particular). Several known ACCase mutations (isoleucine-1781-leucine [Leu], tryptophan-2027-cysteine [Cys], isoleucine-2041-asparagine, and aspartate-2078-Gly) and in particular, a new mutation of Cys to arginine at position 2088, were identified in plants surviving the Australian clethodim field rate (60 g ha(-1)). Twelve combination patterns of mutant alleles were revealed in relation to clethodim resistance. Through a molecular, biochemical, and biological approach, we established that the mutation 2078-Gly or 2088-arginine endows sufficient level of resistance to clethodim at the field rate, and in addition, combinations of two mutant 1781-Leu alleles, or two different mutant alleles (i.e. 1781-Leu/2027-Cys, 1781-Leu/2041-asparagine), also confer clethodim resistance. Plants homozygous for the mutant 1781, 2078, or 2088 alleles were found to be clethodim resistant and cross resistant to a number of other ACCase inhibitor herbicides including clodinafop, diclofop, fluazifop, haloxyfop, butroxydim, sethoxydim, tralkoxydim, and pinoxaden. We established that the specific mutation, the homo/heterozygous status of a plant for a specific mutation, and combinations of different resistant alleles plus herbicide rates all are important in contributing to the overall level of herbicide resistance in genetically diverse, cross-pollinated Lolium species.
Herbicides targeting grass plastidic acetyl coenzyme A carboxylase (ACC) are effective
selective graminicides. Their intensive use worldwide has selected for resistance genes
in a number of grass weed species. Biochemistry and molecular biology have been
the means of determining the herbicidal activity and selectivity toward crop plants
of ACC-inhibiting herbicides. In recent years, elucidation of the tridimensional structure
of ACC and identification of five amino acid residues within the ACC carboxyl
transferase domain that are critical determinants for herbicide sensitivity shed light
on the basis of ACC-based resistance to herbicides. However, metabolism-based resistance
to ACC-inhibiting herbicides is much less well known, although this type
of resistance seems to be widespread. A number of genes thus endow resistance to
ACC-inhibiting herbicides, with the possibility for various resistance genes that confer
dominant resistance at the herbicide field rate to accumulate within a single weed
population or plant. This, together with a poor knowledge of the genetic parameters
driving resistance, renders the evolution of resistance to ACC-inhibiting herbicides
unpredictable. Future research should consider developing tactics to slow the spread
of resistance. For this purpose, it is crucial that our understanding of metabolismbased
resistance improves rapidly because this mechanism is complex and can confer
resistance to herbicides with different target sites.
Pinoxaden is a new grass active compound discovered by Syngenta Crop Protection AG, Basel, Switzerland. The innovative molecule belongs to the phenlypyrazolin chemistry and is being developed for global use in cereal crops. Pinoxaden is applied post-emergence at use rates of 30-60 g ai/ha and active against a wide range of important grass weed species (Alopecurus myosuroides, Apera spica-venti, Avena spp., Lolium spp, Phalaris spp. and Setaria spp.). Tolerance in key cereal crops - including both wheat and barley - is obtained by incorporating the proprietary safener cloquintocet-mexyl into an easy-to-use liquid formulation, which delivers maximal performance when used with a specially optimized adjuvant. Due to its high level of activity against most important grass weeds, its tolerance in wheat and barley crops combined with a wide application window from early to late post-emergence and rotational freedom to following crops, pinoxaden will set a new standard in grass weed control in cereals. Starting from 2006, pinoxaden will be introduced as AXIAL® into cereal markets globally.
A reliable seedling bioassay was developed and tested for the rapid screening for resistance to aryloxyphenoxypropionic (APP) herbicides in Alopecurus myosuroides and Lolium spp. populations. It is based upon the difference in coleoptile length of resistant and susceptible A. myosuroides and Lolium seedlings, respectively, exposed to fenoxaprop-P acid and diclofop acid solution for 6 days in a plastic box. A 6 mg L−1 fenoxaprop-P acid solution was selected as the best concentration for a reliable screening of resistant biotypes within A. myosuroides populations. At this concentration, coleoptile lengths of susceptible and resistant seedlings were shorter and longer than 10 mm respectively. Similarly, resistant seedlings within Lolium populations were easily detected at 10 mg L−1 diclofop acid. At this concentration, coleoptile lengths of susceptible and resistant seedlings were shorter and longer than 20 mm respectively. For both populations, the coleoptile length distributions appear to discriminate between two kinds of APP-resistant biotypes (highly and slightly resistant).
Etiolated shoot segments of wheat (Triticum aestivum L. cv. Fredrick) and barley (Hordeum vulgare L. cv. Legér) were incubated in buffer amended with the herbicides fenoxaprop-ethyl (FE) or diclofop-methyl (DM) and the metabolic inhibitors tetcyclacis (Tc) or tridiphane (Tf). In the absence of the metabolic inhibitors, FE was more rapidly metabolized to polar compounds in wheat than in barley, while the rate of metabolism of DM was similar in the two grass species. Tc inhibited the metabolism of DM and FE in both wheat (98%) and barley (53%), suggesting a possible role of a cytochrome P450-dependent monooxygenase in the detoxification of the two herbicides. The inhibiting effect of Tc was stronger for DM than for FE. Tf did not affect the metabolism of FE in either barley or wheat. The metabolism of DM was reduced by Tf (27%) in wheat. However, this inhibition was significantly less than that of Tc. The herbicide safener, fenchlorazole-ethyl (FCE), enhanced the metabolism of FE in both barley and wheat without affecting the pattern of metabolism. The effect of FCE on FE metabolism was annulled by Tc and Tf in both plant species.
Microsomes isolated from shoot tissues of etiolated wheat seedlings (Triticum aestivum L. var. Olaf) oxidized the sulfonylurea herbicide prosulfuron (CGA 152005). One major and two minor enzymatic oxidation products were isolated and identified by negative ion FAB/MS and cochromatography (TLC and HPLC) with reference standards. Identification of the major oxidation product (I) as 1-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-5-hydroxyphenylsulfonyl]urea was confirmed by proton NMR spectroscopy. Minor oxidation products were tentatively identified as 1-[4-(hydroxymethyl)-6-methoxy-1,3,5-triazin-2-yl]-3-[2-(3,3,3-trifluoropropyl)phenylsulfonyl]urea (II) and an intermediate oxidation product 1-[4-[(hydroxymethyl)oxy]-6-methyl]-1,3,5-triazin-2-yl]-3-[2-(3,3,3-trifluoropropyl)phenylsulfonyl]urea (III) that degraded to 1-(4-hydroxy-6-methyl-1,3,5-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)phenylsulfonyl]urea (IV). Microsomal oxidation of prosulfuron required NADPH and molecular oxygen. Constitutive enzyme activity was increased 5−28-fold by induction with ethanol and with the herbicide safeners naphthalic anhydride or cloquintocet-mexyl (CGA 185072) and by combinations of naphthalic anhydride or cloquintocet-mexyl with ethanol. Inhibition of enzyme activity by CO in the dark was reversible by light. Other inhibitors of prosulfuron oxidation included tetcyclacis, piperonyl butoxide, cytochrome c, polyclonal antibodies raised against wheat cytochrome c (P450) reductase, and the herbicides bifenox and linuron. Kinetic studies established that the apparent Km for prosulfuron was 12.6 ± 1.1 μM and that bifenox and linuron were noncompetitive and mixed-type inhibitors of prosulfuron oxidation, respectively, with apparent Ki values of 210 and 59 μM. Keywords: Wheat; microsomes; prosulfuron oxidation; cytochrome P450
Safeners are chemical agents that reduce the phytotoxicity of herbicides to crop plants by a physiological or molecular mechanism, without compromising weed control efficacy. Commercialized safeners are used for the protection of large-seeded grass crops, such as corn, grain sorghum, and wet-sown rice, against preplant-incorporated or preemergence-applied herbicides of the thiocarbamate and chloroacetanilide families. Safeners also have been developed to protect winter cereal crops such as wheat against postemergence applications of aryloxyphenoxypropionate and sulfonylurea herbicides. The use of safeners for the protection of corn and rice against sulfonylurea, imidazolinone, cyclohexanedione, isoxazole, and triketone herbicides also is well established. A safener-induced enhancement of herbicide detoxification in safened plants is widely accepted as the major mechanism involved in safener action. Safeners induce cofactors such as glutathione and herbicide-detoxifying enzymes such as glutathione S-transferases, cytochrome P450 monooxygenases, and glucosyl transferases. In addition, safeners enhance the vacuolar transport of glutathione or glucose conjugates of selected herbicides. The safener-mediated induction of herbicide-detoxifying enzymes appears to be part of a general stress response. Nomenclature: Corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench; rice, Oryza sativa L.; wheat, Triticum aestivum L.
Seeds from five suspected acetyl-CoA carboxylase (ACCase) inhibitor-resistant wild oat biotypes (R1 to R5) were collected in wheat and lentil fields in the Pacific Northwest. Based on whole plant dose-response experiments, the five resistant biotypes were 2 to 24 times more resistant to the aryloxyphenoxypropionate (APP) herbicides (fenoxaprop, diclofop, and quizalofop) compared with the susceptible biotype. However, none of the resistant biotypes were resistant to the cyclohexanedione (CHD) herbicides, sethoxydim and clethodim. R2 was the only biotype resistant to tralkoxydim and pinoxaden, a phenylpyrazolin herbicide and an ACCase inhibitor. The R2 biotype was 35 and 16 times more resistant to tralkoxydim and pinoxaden, respectively, when compared with the susceptible biotype. The levels of resistance and cross-resistance patterns varied among biotypes indicating either more than one mechanism of resistance or different resistance mutations in these wild oat biotypes. The CHD herbicides, sethoxydim and clethodim, could be used to control these resistant biotypes. Except for the R2 biotype, pinoxaden could be used to control the resistant wild oat biotypes. The resistance patterns of these wild oat biotypes are an indication of the difficulty in predicting cross-resistance among the ACCase inhibitor herbicides.
Primers were designed to amplify two regions involved in sensitivity to herbicides inhibiting the plastidic acetyl-CoA carboxylase (ACCase) from grasses (Poaceae). The first primer pair amplified a 551-bp amplicon containing a variable Ile/Leu codon at position 1781 in Alopecurus myosuroides sequence. The second primer pair amplified a 406-bp amplicon containing four variable codons (Trp/Cys, Ile/Asn, Asp/Gly, Gly/Ala) at positions 2027, 2041, 2078 and 2096, respectively, in A. myosuroides sequence. Both primer pairs amplified the targeted fragments from genes encoding plastidic ACCases, but not from the very similar genes encoding cytosolic ACCases. Clear DNA sequences were obtained from fresh or dried plant material from the field, and from 29 various grass species. Sequences revealed that the gene encoding plastidic ACCase in Poa annua and Festuca rubra contained a Leu1781 codon, in agreement with both species being inherently tolerant to herbicides inhibiting ACCase. Sequencing confirmed the hybrid origin of P. annua. Compared with ACCase enzyme assay, polymerase chain reaction is faster, can be performed from a single plant and suppresses the need for radioactive experiments. It can be completed with basic molecular biology laboratory equipment. It is the tool of choice for diagnosing resistance caused by alteration(s) of the plastidic ACCase.
The high adoption of chemical weed control and the broad range of solutions already available to manage most weed problems are significant hurdles to the development and launch of new herbicides. Business potentials are influenced by the high technical and biological standards provided by existing herbicides, as well as the intense competition in the marketplace. Other factors adding complexity are agronomic, structural and technological changes, including the introduction of herbicide-tolerant crops, and the high costs of development for new active ingredients, mainly due to increasing regulatory requirements. In the light of increasing weed resistance to widely used herbicides, securing diversity in agronomy as well as weed management is a key to efficient crop production in future. In order to support this objective, new herbicides, preferably with new modes-of-action, will need to be discovered and developed.
The effect of the herbicide safener mefenpyr-diethyl on glutathione S-transferase (GST, EC 2.5.1.18) activities of dark-grown barley (Hordeum vulgare cv. Alexis) was examined. Mefenpyr-diethyl treatment increased the GST activity with 1-chloro-2,4-dinitrobenzene (CDNB) and the herbicide fenoxaprop as substrates. Glutathione (GSH) peroxidase activity was markedly increased. GST subunits were analysed by high performance liquid chromatography (HPLC). The quantities of two major subunits were increased by the safener treatment, while the quantities of two other major subunits remained constant. A cDNA encoding the most abundant inducible GST (HvGST6) was cloned and expressed in E. coli. The purified enzyme exhibited a low activity with herbicides as substrates. By contrast, it exhibited a strong GSH peroxidase activity.
Due to heavy reliance on herbicides and a lack of cultural control measures, herbicide-resistant populations of Alopecurus myosuroides Huds. (blackgrass) appeared in the early 1990s in winter cereal rotations in France and in Europe. The aim of the present study was to analyse the effects of different cropping systems on an aryloxy-phenoxypropionate herbicide-resistant population in a field trial. Two crop rotations, one consisting exclusively of winter crops and another including spring crops, were assessed over a six-year period. The rotations were combined with different cultural practices including mouldboard ploughing, delayed sowing, and efficient herbicides for controlling resistant plants. A. myosuroides densities decreased in all the cropping systems, but the weed management was most effective when herbicides were combined with non-chemical practices. Rotation with an alternation of spring and winter crops was the most efficient solution against A. myosuroides. Moreover, during the six years, the percentage of resistant plants in different crop rotations was estimated independently of the cropping systems. This proportion did not vary during the six years of the experiment, suggesting that the resistance gene persisted, despite the removal of selection pressure by the aryloxy-phenoxypropionate herbicides.
The process of evolution of resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides was investigated in four distinct patches of Alopecurus myosuroides Huds. (black-grass) that occur within adjacent fields on a cereal farm in Nottinghamshire, UK. In one field, there was a `main' patch containing 96% resistant plants and two `satellite' patches containing ≈2.9% and 4.4% resistant plants, and in an adjacent field another patch contained 25% resistant plants. Genome fingerprinting by simple sequence repeat (SSR)-anchored polymerase chain reaction (PCR) was used to analyse variation at 30 genetic loci in at least 20 resistant and 20 sensitive individual plants from each patch, from additional resistant populations from Essex and Lincolnshire, and from a sensitive reference population. Banding patterns were found to be highly repeatable. Each patch contained a high level of genetic diversity, regardless of its resistance status, and there was evidence for genetic differences between the patches (Gst = 0.14, Nei's distances up to 0.26). There was no evidence that resistance had spread from the `main' patch to the others, as resistant and sensitive plants in the same patch were more closely related on average than were resistant plants from neighbouring patches. The most likely explanations of this distribution, and their implications, are discussed.
We assessed the contributions of target site- and non-target site-based resistance to herbicides inhibiting acetyl-coenzyme A carboxylase (ACC) in Alopecurus myosuroides (black grass). A total of 243 A. myosuroides populations collected across France were analysed using herbicide sensitivity bioassay (24 300 seedlings analysed) and ACC genotyping (13 188 seedlings analysed). Seedlings resistant to at least one ACC-inhibiting herbicide were detected in 99.2% of the populations. Mutant, resistant ACC allele(s) were detected in 56.8% of the populations. Among the five resistant ACC alleles known in A. myosuroides, alleles containing an isoleucine-to-leucine substitution at codon 1781 were predominant (59.5% of the plants containing resistant ACC alleles). Comparison of the results from herbicide sensitivity bioassays with genotyping indicated that more than 75% of the plants resistant to ACC-inhibiting herbicides in France would be resistant via increased herbicide metabolism. Analysis of herbicide application records suggested that in 15.9% of the populations studied, metabolism-based resistance to ACC-inhibiting herbicides was mostly selected for by herbicides with other modes of action. Our study revealed the importance of non-target site-based resistance in A. myosuroides. Using herbicides with alternative modes of action to control populations resistant to ACC-inhibiting herbicides, the recommended management approach, may thus be jeopardised by the widespread occurrence of metabolism-based resistance mechanisms conferring broad-spectrum cross-resistance.
Phalaris paradoxa (awned canary-grass) is an aggressive annual winter weed in wheat and other arable crops that is controlled mainly by ACCase-inhibiting herbicides: cyclohexanediones (DIMs), aryloxyphenoxypropionates (FOPs) and phenylpyrazolines (DENs, e.g. pinoxaden). The selection pressure imposed on the weed populations by repeated use of these herbicides has resulted in the evolution of increased numbers of ACCase-resistant populations of P. paradoxa in Israel and other countries. Two populations, Revadim (RV) and Mishmar Ha’emek (MH) that were exposed to differing weed and crop management tactics were investigated. Both populations were highly resistant to all FOPs, pinoxaden and cycloxydim, but responded differently to some DIMs. RV plants exhibited much higher resistance to tralkoxydim than MH plants, while showing similar low levels of resistance to tepraloxydim and clethodim. Both populations were equally susceptible to graminicides with other modes of action. The mutations responsible for the observed resistance were identified using PCR-RFLP and by sequencing the carboxyl transferase domain of the chloroplastic ACCase gene. RV plants possess a substitution of Asp2078 to Gly, whereas in MH population a mixture of Ile2041 to Asn or Asp2078 to Gly was found. Our study demonstrates that lack of herbicide and crop rotation may result in the evolution of diverse target site mutations and differential response of the whole plant to ACCase inhibitors.
A blackgrass population has developed resistance to fenoxaprop-P-ethyl following field selection with the herbicide for 6
consecutive years. Within this population, 95% of the individuals are also resistant to flupyrsulfuron. Both the inheritance(s)
and the mechanism(s) of resistances were investigated by making crosses between the resistant and a susceptible biotype. The
inheritance was followed through the F1 and F2 generations either by spraying the herbicide on seedlings at the three-leaf stage or using a seedling bioassay, based on
coleoptile length. No maternal effects were evident in the fenoxaprop-P-ethyl responses of the F1 plants, suggesting that the inheritance was nuclear. Some F1 families treated with fenoxaprop-P-ethyl segregated in a 3:1 (resistant:susceptible) ratio, indicating that the resistance
was conferred by two dominant and independent nuclear genes. This was confirmed by the 15:1 (R:S) ratio observed in the F2 generation treated with fenoxaprop- P-ethyl. The use of selective inhibitors of herbicide de-toxifying enzymes (aminobenzotriazole,
pyperonylbutoxide, malathion and tridiphane) with the F2 plants suggested that each of the two genes may govern two different mechanisms of fenoxaprop-P-ethyl resistance: the ACCase
mutation previously postulated and an enhanced herbicide metabolism, mediated by cytochrome P 450 mono-oxygenases (P 450)
susceptible to malathion. The P 450 activity may also confer resistance to flupyrsulfuron. This study clearly indicates that
two distinct mechanisms of resistance may co-exist in the same plant.
Diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate) was hydrolyzd rapidly to diclofop (2-[4-(2′,4′-dichlorophenoxy)phenoxy]propionic acid) in resistant wheat and susceptible wild oat. Neither compound accumulated in the tissues of either species. The major reactions in wheat are the oxygenation of the 2,4-dichlorophenyl moiety of diclofop, followed by conjugation to an acidic aryl glycoside. In wild oat, diclofop was conjugated as a neutral glycosyl ester. The sugar moiety has not been characterized positively in either conjugate. Only limited symplastic and apoplastic translocation of diclofop-methyl and its metabolites occurred in wheat and wild oat. Herbicide selectivity between wheat and wild oat may be a function of its placement on the plant and the rate of herbicide metabolism, but the ability of wheat to irreversibly detoxify the herbicide by aryl hydroxylation may be the primary selective factor.
Black-grass (Alopecurus myosuroides) is a major weed of wheat in Europe, with several populations having acquired resistance to multiple herbicides of differing modes of action. As compared with herbicide-susceptible black-grass, populations showing herbicide cross-resistance contained greatly elevated levels of a specific type I glutathione transferase (GST), termed AmGST2, but similar levels of a type III GST termed AmGST1. Following cloning and expression of the respective cDNAs, AmGST2 differed from AmGST1 in showing limited activity in detoxifying herbicides but high activities as a glutathione peroxidase (GPOX) capable of reducing organic hydroperoxides. In contrast to AmGST2, other GPOXs were not enhanced in the herbicide-resistant populations. Treatment with a range of herbicides used to control grass weeds in wheat resulted in increased levels of hydroperoxides in herbicide-susceptible populations but not in herbicide-resistant plants, consistent with AmGST2 functioning to prevent oxidative injury caused as a primary or secondary effect of herbicide action. Increased AmGST2 expression in black-grass was associated with partial tolerance to the peroxidizing herbicide paraquat. The selective enhancement of AmGST2 expression resulted from a constitutively high expression of the respective gene, which was activated in herbicide-susceptible black-grass in response to herbicide safeners, dehydration and chemical treatments imposing oxidative stress. Our results provide strong evidence that GSTs can contribute to resistance to multiple herbicides by playing a role in oxidative stress tolerance in addition to detoxifying herbicides by catalysing their conjugation with glutathione.
A simple method based upon allele‐specific PCR was developed to detect an isoleucine‐leucine substitution in the gene encoding chloroplastic acetyl‐coenzyme A carboxylase (ACCase) in two gramineous weeds: Lolium rigidum Gaud and Alopecurus myosuroides Huds. Analysis of 1800 A myosuroides and 750 L rigidum seedlings showed that the presence of ACCase leucine allele(s) conferred cross‐resistance to the cyclohexanedione herbicide cycloxydim and to the aryloxyphenoxypropionate herbicides fenoxaprop‐P‐ethyl and diclofop‐methyl. Seedlings containing ACCase leucine allele(s) could be either sensitive or resistant to the aryloxyphenoxypropionate herbicides haloxyfop‐P‐methyl and clodinafop‐propargyl. Successful detection of resistant plants in a field population of A myosuroides was achieved using this PCR assay. Using it with basic molecular biology laboratory equipment, the presence of resistant leucine ACCase allele(s) can be detected within one working day.
© 2002 Society of Chemical Industry
The expression of glutathione S-transferase (GST) activity in wheat and maize shoots was investigated in response to treatments with the herbicide safeners benoxacor, cloquintocet-mexyl, fenchlorazole-ethyl, fenclorim, fluxofenim and oxabetrinil. These safeners significantly enhanced the GST activity towards 1-chloro-2,4-dinitrobenzene (CDNB) as a 'standard' substrate, with the exception of oxabetrinil in maize. The enhancements of GST (CDNB) activity were found to be concomitant with increases in V(max) (the reaction rate when the enzyme is fully saturated by the substrate) in wheat following cloquintocet-mexyl and fenchlorazole-ethyl treatments, and in maize following fenchlorazole-ethyl treatment. Otherwise, decreases in V(max) were observed in wheat and maize following fenclorim and fluxofenim treatments. With the exception of oxabetrinil, all the safeners significantly reduced the apparent K(M) (the substrate concentration required for 50% of maximum GST activity) of both wheat and maize GST. The V(max) and K(M) variations following safener treatments are discussed in terms of an increased expression of GST enzymes and an increased affinity for the CDNB substrate. The activity of wheat and maize GST was also assayed towards butachlor and terbuthylazine respectively; the results indicate the ability of cloquintocet-mexyl, fenchlorazole-ethyl and fluxofenim to enhance the enzyme activity in wheat and of benoxacor and fenchlorazole-ethyl to do so in maize.
Effective herbicide resistance management requires an assessment of the range of spatial dispersion of resistance genes among weed populations and identification of the vectors of this dispersion. In the grass weed Alopecurus myosuroides (black-grass), seven alleles of the acetyl-CoA carboxylase (ACCase) gene are known to confer herbicide resistance. Here, we assessed their respective frequencies and spatial distribution on two nested geographical scales (the whole of France and the French administrative district of Côte d'Or) by genotyping 13 151 plants originating from 243 fields. Genetic variation in ACCase was structured in local populations at both geographical scales. No spatial structure in the distribution of resistant ACCase alleles and no isolation by distance were detected at either geographical scale investigated. These data, together with ACCase sequencing and data from the literature, suggest that evolution of A. myosuroides resistance to herbicides occurred at the level of the field or group of adjacent fields by multiple, independent appearances of mutant ACCase alleles that seem to have rather restricted spatial propagation. Seed transportation by farm machinery seems the most likely vector for resistance gene dispersal in A. myosuroides.
Acetyl coenzyme A carboxylase (ACCase) is the target of highly effective herbicides. We investigated the nucleotide variability of the ACCase gene in a sample of 18 black-grass (Alopecurus myosuroides [Huds.]) populations to search for the signature of herbicide selection. Sequencing 3,396 bp encompassing ACCase herbicide-binding domain in 86 individuals revealed 92 polymorphisms, which formed 72 haplotypes. The ratio of nonsynonymous versus synonymous substitutions was very low, in agreement with ACCase being a vital metabolic enzyme. Within black grass, most nonsynonymous substitutions were related to resistance to ACCase-inhibiting herbicides. Differentiation between populations was strong, in contrast to expectations for an allogamous, annual plant. Significant H tests revealed recent hitchhiking events within populations. These results were consistent with recent and local positive selection. We propose that, although they have only been used since at most 15 black-grass generations, ACCase-inhibiting herbicides have exerted a positive selection targeting resistant haplotypes that has been strong enough to have a marked effect upon ACCase nucleotide diversity. A minimum-spanning network of nonrecombinant haplotypes revealed multiple, independent apparitions of resistance-associated mutations. This study provides the first evidence for the signature of ongoing, recent, pesticide selection upon variation at the gene encoding the targeted enzyme in natural plant populations.
We have witnessed a dramatic increase in the frequency and diversity of herbicide-resistant weed biotypes over the past two decades, which poses a threat to the sustainability of agriculture at both local and global levels. In addition, non-target-site mechanisms of herbicide resistance seem to be increasingly implicated. Non-target-site herbicide resistance normally involves the biochemical modification of the herbicide and/or the compartmentation of the herbicide (and its metabolites). In contrast to herbicide target site mutations, fewer non-target mechanisms have been elucidated at the molecular level because of the inherently complicated biochemical processes and the limited genomic information available for weedy species. To further understand the mechanisms of non-target-site resistance, we propose an integrated genomics approach to dissect systematically the functional genomics of four gene families in economically important weed species.
Target-site-based resistance to acetyl-CoA carboxylase (ACCase) inhibitors in Alopecurus myosuroides Huds. is essentially due to five substitutions (Isoleucine-1781-Leucine, Tryptophan-2027-Cysteine, Isoleucine-2041-Asparagine, Aspartate-2078-Glycine, Glycine-2096-Alanine). Recent studies suggested that cross-resistance patterns associated with each mutation using a seed-based bioassay may not accurately reflect field resistance. The authors aimed to connect the presence of mutant ACCase isoform(s) in A. myosuroides with resistance to five ACCase inhibitors (fenoxaprop, clodinafop, haloxyfop, cycloxydim, clethodim) sprayed at the recommended field rate.
Results from spraying experiments and from seed-based bioassays were consistent for all mutant isoforms except the most widespread, Leucine-1781. In spraying experiments, Leucine-1781 ACCase conferred resistance to clodinafop and haloxyfop. Some plants containing Leucine-1781 or Alanine-2096 ACCase, but not all, were also resistant to clethodim.
Leucine-1781, Cysteine-2027, Asparagine-2041 and Alanine-2096 ACCases confer resistance to fenoxaprop, clodinafop and haloxyfop at field rates. Leucine-1781 ACCase also confers resistance to cycloxydim at field rate. Glycine-2078 ACCase confers resistance to all five herbicides at field rates. Only Glycine-2078 ACCase confers clethodim resistance under optimal application conditions. It may be that Leucine-1781 and Alanine-2096 ACCases may also confer resistance to clethodim in the field if the conditions are not optimal for herbicide efficacy, or at reduced clethodim field rates.
Studies on induction of wheat cytochrome P450 by mefenpyr-diethyl and its spectrum characteristics
- Z Gao
- J Jiang
- X Li
- L Qiu
- Wang C Zhang
Gao Z, Jiang J, Li X, Qiu L, Wang C and Zhang W, Studies on induction
of wheat cytochrome P450 by mefenpyr-diethyl and its spectrum
characteristics. Plant Protec 31:40-44 (2005).
Single-site mutations in the carboxyltransferase domain of plastid acetyl-CoA carboxylase confer resistance to grass-specific herbicides
- W Liu
- D K Harrison
- D Chalupska
- P Gornicki
- O' Donnell
- C C Adkins
Liu W, Harrison DK, Chalupska D, Gornicki P, O'Donnell CC, Adkins SW,
et al, Single-site mutations in the carboxyltransferase domain of
plastid acetyl-CoA carboxylase confer resistance to grass-specific
herbicides. Proc Natl Acad Sci U S A 104:3627-3632 (2007).
International Survey of Herbicide Resistant Weeds
- I Heap
Heap I, International Survey of Herbicide Resistant Weeds. [Online].
Available: http://www.weedresearch.com [11 February 2009].
Studies on induction of wheat cytochrome P450 by mefenpyr‐diethyl and its spectrum characteristics
- Gao Z