Non-target Site Research Articles

Metproxybicyclone, a Novel Carbocyclic Aryl-dione Acetyl-CoA Carboxylase-Inhibiting Herbicide for the Management of Sensitive and Resistant Grass Weeds.

Postemergence control of grass weeds has become problematic due to the evolution of resistance to 5-enolpyruvylshikimate-3-phosphate synthase, acetyl-CoA carboxylase (ACCase), and acetolactate synthase-inhibiting herbicides. Herein we describe the invention and synthesis journey toward metproxybicyclone, the first commercial carbocyclic aryl-dione ACCase-inhibiting herbicide for the cost-effective management of grass weeds in dicotyledonous crops and in preplant burndown applications. Glasshouse and field experiments have shown that metproxybicyclone is safe for use on soybean, cotton, and sugar beet, among other crops. It is effective on a variety of key grass weeds including Eleusine indica, Digitaria insularis, Sorghum halepense, and Echinochloa crus-galli. Importantly, metproxybicyclone was more efficacious at killing resistant grass weed populations than current ACCase herbicides. Metproxybicyclone controlled the main ACCase target-site and nontarget site resistant mechanisms in characterized Lolium multiflorum and E. indica populations under glasshouse conditions. Excellent control of a broad resistance-causing D2078G target-site mutant E. indica population was also observed under field conditions.

Fungicide Sensitivity and Non-Target Site Resistance in Rhizoctonia zeae Isolates Collected from Corn and Soybean Fields in Nebraska.

Rhizoctonia zeae was recently identified as the major Rhizoctonia species in corn and soybean fields in Nebraska and was shown to be pathogenic on corn and soybean seedlings. Fungicide seed treatments commonly used to manage seedling diseases include prothioconazole (demethylation inhibitor), fludioxonil (phenylpyrrole), sedaxane (succinate dehydrogenase inhibitor), and azoxystrobin (quinone outside inhibitor; QoI). To establish the sensitivity of R. zeae to these fungicides, we isolated this pathogen from corn and soybean fields in Nebraska during 2015 to 2017 and estimated the relative effective concentration for 50% inhibition (EC50) of a total of 91 R. zeae isolates from Nebraska and Illinois. Average EC50 for prothioconazole, fludioxonil, sedaxane, and azoxystrobin was 0.219, 0.099, 0.078, and > 100 µgml-1, respectively. In planta assays showed that azoxystrobin did not significantly reduce the disease severity on soybean (P > 0.05). The cytochrome b gene of R. zeae did not harbor any mutation known to confer QoI resistance and had a type-I intron directly after codon 143 suggesting that a G143A mutation is unlikely to evolve in this pathogen. For prothioconazole, fludioxonil, and sedaxane, EC50 of isolates did not differ significantly among years of collection (P > 0.05) and their single discriminatory concentrations were identified as 0.1 µgml-1. This is the first study to establish non-target site resistance of R. zeae to azoxystrobin and the sensitivity of R. zeae to commonly used seed treatment fungicides in Nebraska. This information will help to guide strategies for chemical control of R. zeae and monitor sensitivity shifts in future.

Involvement of P450s in the metabolic resistance of Digitaria sanguinalis (L.) Scop. To ALS-inhibiting herbicides

Weed resistance to a range of herbicides has rapidly evolved, often with different mechanisms of action. The resulting uninhibited growth of weeds poses demonstrable threats to crop production and sustainable agriculture. Digitaria sanguinalis (L.) Scop., a troublesome weed in corn and other agricultural fields, has developed resistance to herbicides that inhibiting ALS (Acetolactate Synthase), such as nicosulfuron. Understanding the weed's resistance patterns and mechanisms is crucial. However, little is known of the non-target site resistance (NTSR) mechanisms of D. sanguinalis owing to a lack of relevant genome sequences and other materials. Therefore, in this study, a population of D.sanguinalis presenting multiple resistance was tested and found that its high level of resistance to ALS-inhibiting herbicides was not associated with target-related alterations.Administration of P450 inhibitors reversed the resistance to ALS-inhibiting herbicides. Following the application of ALS-inhibiting herbicides, the activities of NADPH-P450 reductase and p-nitroanisole O-demethylase (PNOD) were notably greater in the resistant population of D. sanguinalis than those in the susceptible population. The results suggested P450 enzyme familyplays a major role in the metabolic resistance mechanism, that increased P450 enzyme activity promote cross-resistance in D. sanguinalis to ALS-inhibiting herbicides. RNA-seq analysis showed that five genes from the P450 family (CYP709B2, CYP714C2, CYP71A1, CYP76C2, and CYP81E8) were upregulated in resistant D. sanguinalis. In conclusion, the upregulation of several P450 genes is responsible for establishing resistance to ALS-inhibiting herbicides in D. sanguinalis.

Preliminary monitoring of knockdown resistance (kdr) mutation in Anopheles stephensi: insights from a malarious area in Southeastern Iran

BackgroundAnopheles stephensi is recognized as the main malaria vector in Iran. In recent years, resistance to several insecticide classes, including organochlorine, pyrethroids, and carbamate compounds, has been reported for this medically important malaria vector. The main objective of the present study was to evaluate the insecticide susceptibility status of An. stephensi collected from the southern part of Iran, and to clarify the mechanism of resistance, using bioassay tests and molecular methods comparing the sequence of susceptible and resistant mosquitoes.MethodsMosquito larvae were collected from various larval habitats across six different districts (Gabrik, Sardasht, Tidar, Dehbarez, Kishi and Bandar Abbas) in Hormozgan Provine, located in the southern part of Iran. From each district standing water areas with the highest densities of Anopheles larvae were selected for sampling, and adult mosquitoes were reared from them. Finally, the collected mosquito species were identified using valid keys. Insecticide susceptibility of An. stephensi was tested using permethrin 0.75%, lambdacyhalothrin 0.05%, deltamethrin 0.05%, and DDT 4%, following the World Health Organization (WHO) test procedures for insecticide resistance monitoring. Additionally, knockdown resistance (kdr) mutation in the voltage-gated sodium channel (vgsc) gene was sequenced and analysed among resistant populations to detect possible molecular mechanisms of observed resistance phenotypes.ResultsThe susceptibility status of An. stephensi revealed that resistance to DDT and permethrin was found in all districts. Furthermore, resistance to all tested insecticides in An. stephensi was detected in Gabrik, Sardasht, Tidar, and Dehbarez. Analysis of knockdown resistance (kdr) mutations at the vgsc did not show evidence for the presence of this mutation in An. stephensi.ConclusionBased on the results of the current study, it appears that in An. stephensi from Hormozgan Province (Iran), other resistance mechanisms such as biochemical resistance due to detoxification enzymes may be involved due to the absence of the kdr mutation or non-target site resistance. Further investigation is warranted in the future to identify the exact resistance mechanisms in this main malaria vector across the country.

Sublethal dosing exposure risk of kochia (Bassia scoparia (L.) A.J. Scott) to carfentrazone-ethyl

Kochia is a troublesome, multiple herbicide-resistant tumbleweed which infests Prairie field crops. Kochia has developed resistance to systemic, foliar-applied herbicides from groups 2, 4, and 9, leaving only contact herbicides for post-emergence control. Group 14 chemistry is an important mode of action for resistance management. Weed staging considerations are important as recurrent sub-lethal herbicide exposure can increase risk of nontarget site resistance evolution. The study objective was to evaluate loss-of-control and estimate sublethal dosing exposure risk (SLDER) with a contact-type herbicide (carfentrazone-ethyl) based on initial kochia height, leaf number, and branch number. The SLDER from a single application to a single plant was conceptualized to increase due to escaping plant “volume” or immediate flowering. Kochia was only consistently controlled (100% injury) when dosed at ≤5 cm in height. The estimated maximum size for treated kochia was 21 cm in height, 18 branches plant−1, and the maximum accumulated biomass was between 2.6 and 5.1 g plant−1 for models developed using the initial plant height, branch number, or leaf number as predictors. These estimates represent the largest plant escapes, which would be associated with 100% risk through vegetative considerations into SLDER. Kochia plant size for a 5% risk scenario using the SLDER model was 4 cm in height, 0 branches plant−1, and 11 leaves plant−1 when carfentrazone-ethyl was applied at the labeled dosing. Caution is advised when spraying kochia above 5 cm as incorrect staging may lead to sublethal exposure, escape, reproduction, and escalated risk of nontarget site resistance evolution.

Occurrence and Mechanisms Conferring Multiple Resistance to ALS-Inhibiting and Auxins Mimics Herbicides in Papaver rhoeas from Tunisia

Herbicide-resistant corn poppy (Papaver rhoeas L.) is one of the most important broadleaved weeds and the number of resistant cases is still growing. The aims of this study were to confirm the resistance of P. rhoeas from Tunisia to ALS inhibitors and auxin mimics and investigate the mechanisms of Target-Site Resistance (TSR) and Non-Target Site Resistance (NTSR) involved. Dose–response trials to determine cross-resistance patterns for ALS inhibitors and auxin mimics were conducted in a greenhouse. In this study, multiple resistance to tribenuron-methyl and dicamba but not to 2,4-D was found in P. rhoeas populations. Cross-resistance to imazamox was confirmed as well. Sequence analysis of the ALS gene detected target-site mutations in codon 197 of the ALS gene, namely, Pro197His, Pro197Thr, Pro197Leu, and Pro197Asn. In this study, the metabolism experiments with malathion (a cytochrome P450 inhibitor) showed that malathion reduced resistance to imazamox, indicating that P450 is involved in the resistance. TSR and NTSR mechanisms to ALS inhibitors likely coexist. The findings of this study revealed a significant synergistic interaction between malathion and dicamba in particular populations, suggesting that the resistance to auxin mimics can be conferred by enhanced metabolism.

Current Status of Auxin‐Mimic Herbicides

The challenge of managing pesticide resistance in modern agriculture has become increasingly daunting. Herbicide resistance presents a complex scenario due to the continuous selection pressure from synthetic herbicides in global agricultural systems. Auxin‐mimic herbicides (AMHs) have traditionally served as a dependable tool for managing resistant weed populations in crop systems. However, overreliance on AMHs because of the lower incidence of resistance compared to other herbicide classes has intensified selection pressure on weed populations. Resistance to AMHs primarily arises from generalist mechanisms such as non-target site resistance (NTSR), involving reduced translocation, absorption, and enhanced metabolism. Nevertheless, specific mechanisms like target site resistance have also emerged in certain problematic weed species. These resistance mechanisms are complex to manage because some of them can confer resistance to single, cross, or multiple herbicide groups with diverse chemical and action mechanisms.

Mechanistic understanding and sustainable management of non-target site herbicide resistance in modern day agriculture

Mechanistic understanding and sustainable management of non-target site herbicide resistance in modern day agriculture

Metabolic Resistance to Protoporphyrinogen Oxidase-Inhibitor Herbicides in a Palmer amaranth Population from Kansas.

Palmer amaranth has evolved target and nontarget site resistance to protoporphyrinogen oxidase-inhibitor herbicides in the United States. Recently, a population (KCTR) from a long-term conservation tillage study in Kansas was found to be resistant to herbicides from six sites of action, including to PPO-inhibitors, even with this herbicide group being minimally used in this field. This research investigated the level of resistance to postemergence PPO-inhibitors, target- and nontarget-site resistance mechanism(s), and efficacy of pre-emergence chemistries. The greenhouse experiments confirmed 6.1- to 78.9-fold resistance to lactofen in KCTR, with the level of resistance increasing when KCTR was purified for the resistance trait. PPO2 sequences alignment revealed the absence of known mutations conferring resistance to PPO-inhibitors in KCTR Palmer amaranth, and differential expression of the PPO2 gene did not occur. KCTR metabolized fomesafen faster than the susceptible population, indicating that herbicide detoxification is the mechanism conferring resistance in this population. Further, treatment with the cytochrome P450-inhibitor malathion followed by lactofen restored the sensitivity of KCTR to this herbicide. Despite being resistant to POST applied PPO-inhibitors, KCTR Palmer amaranth was completely controlled by the labeled rate of the PRE applied PPO-inhibitors fomesafen, flumioxazin, saflufenacil, sulfentrazone, and oxadiazon. The overall results suggest that P450-mediated metabolism confers resistance to PPO-inhibitors in KCTR, rather than alterations in the PPO2, which were more commonly found in other Palmer amaranth populations. Future work will focus on identifying the fomesafen metabolites and on unravelling the genetic basis of metabolic resistance to PPO-inhibitor herbicides in KCTR Palmer amaranth.

RNA and protein biomarkers for detecting enhanced metabolic resistance to herbicides mesosulfuron-methyl and fenoxaprop-ethyl in black-grass (Alopecurus myosuroides).

The evolution of non-target site resistance (NTSR) to herbicides leads to a significant reduction in herbicide control of agricultural weed species. Detecting NTSR in weed populations prior to herbicide treatment would provide valuable information for effective weed control. While not all NTSR mechanisms have been fully identified, enhanced metabolic resistance (EMR) is one of the better studied, conferring tolerance through increased herbicide detoxification. Confirming EMR towards specific herbicides conventionally involves detecting metabolites of the active herbicide molecule in planta, but this approach is time-consuming and requires access to well-equipped laboratories. In this study, we explored the potential of using molecular biomarkers to detect EMR before herbicide treatment in black-grass (Alopecurus myosuroides). We tested the reliability of selected biomarkers to predict EMR and survival after herbicide treatments in both reference and 27 field-derived black-grass populations collected from sites across the UK. The combined analysis of the constitutive expression of biomarkers and metabolism studies confirmed three proteins, namely, AmGSTF1, AmGSTU2 and AmOPR1, as differential biomarkers of EMR toward the herbicides fenoxaprop-ethyl and mesosulfuron in black-grass. Our findings demonstrate that there is potential to use molecular biomarkers to detect EMR toward specific herbicides in black-grass without reference to metabolism analysis. However, biomarker development must include testing at both transcript and protein levels in order to be reliable indicators of resistance. This work is a first step towards more robust resistance biomarker development, which could be expanded into other herbicide chemistries for on-farm testing and monitoring EMR in uncharacterised black-grass populations. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genomic characterisation and dissection of the onset of resistance to acetyl CoA carboxylase-inhibiting herbicides in a large collection of Digitaria insularis from Brazil.

An in-depth genotypic characterisation of a diverse collection of Digitaria insularis was undertaken to explore the neutral genetic variation across the natural expansion range of this weed species in Brazil. With the exception of Minas Gerais, populations from all other states showed high estimates of expected heterozygosity (HE > 0.60) and genetic diversity. There was a lack of population structure based on geographic origin and a low population differentiation between populations across the landscape as evidenced by average Fst value of 0.02. On combining haloxyfop [acetyl CoA carboxylase (ACCase)-inhibiting herbicide] efficacy data with neutral genetic variation, we found evidence of presence of two scenarios of resistance evolution in this weed species. Whilst populations originating from north-eastern region demonstrated an active role of gene flow, populations from the mid-western region displayed multiple, independent resistance evolution as the major evolutionary mechanism. A target-site mutation (Trp2027Cys) in the ACCase gene, observed in less than 1% of resistant populations, could not explain the reduced sensitivity of 15% of the populations to haloxyfop. The genetic architecture of resistance to ACCase-inhibiting herbicides was dissected using a genome wide association study (GWAS) approach. GWAS revealed association of three SNPs with reduced sensitivity to haloxyfop and clethodim. In silico analysis of these SNPs revealed important non-target site genes belonging to families involved in herbicide detoxification, including UDPGT91C1 and GT2, and genes involved in vacuolar sequestration-based degradation pathway. Exploration of five genomic prediction models revealed that the highest prediction power (≥0.80) was achieved with the models Bayes A and RKHS, incorporating SNPs with additive effects and epistatic interactions, respectively.

Revisiting the origins of glyphosate-resistant giant ragweed (Ambrosia trifida L.) in Canada

Glyphosate-resistant giant ragweed ( Ambrosia trifida L.) was first identified in Canada in 2008. Although early studies attributed resistance in this species solely to non-target site mechanisms, the presence of a proline (P) to serine (S) mutation at position 106 of EPSPS2 in common and giant ragweed has recently been reported. The objective of this research was (i) to determine whether a P106S mutation is present in historical samples of giant ragweed seed collected from the site of the first report of glyphosate resistance, and (ii) to determine the frequency and distribution of P106S in resistant and susceptible biotypes collected as part of historical surveys throughout southwestern Ontario.

Enhanced metabolic detoxification is associated with fluroxypyr resistance in Bassia scoparia.

Auxin-mimic herbicides chemically mimic the phytohormone indole-3-acetic-acid (IAA). Within the auxin-mimic herbicide class, the herbicide fluroxypyr has been extensively used to control kochia (Bassia scoparia). A 2014 field survey for herbicide resistance in kochia populations across Colorado identified a putative fluroxypyr-resistant (Flur-R) population that was assessed for response to fluroxypyr and dicamba (auxin-mimics), atrazine (photosystem II inhibitor), glyphosate (EPSPS inhibitor), and chlorsulfuron (acetolactate synthase inhibitor). This population was resistant to fluroxypyr and chlorsulfuron but sensitive to glyphosate, atrazine, and dicamba. Subsequent dose-response studies determined that Flur-R was 40 times more resistant to fluroxypyr than a susceptible population (J01-S) collected from the same field survey (LD50 720 and 20 g ae ha-1, respectively). Auxin-responsive gene expression increased following fluroxypyr treatment in Flur-R, J01-S, and in a dicamba-resistant, fluroxypyr-susceptible line 9,425 in an RNA-sequencing experiment. In Flur-R, several transcripts with molecular functions for conjugation and transport were constitutively higher expressed, such as glutathione S-transferases (GSTs), UDP-glucosyl transferase (GT), and ATP binding cassette transporters (ABC transporters). After analyzing metabolic profiles over time, both Flur-R and J01-S rapidly converted [14C]-fluroxypyr ester, the herbicide formulation applied to plants, to [14C]-fluroxypyr acid, the biologically active form of the herbicide, and three unknown metabolites. The formation and flux of these metabolites were faster in Flur-R than J01-S, reducing the concentration of phytotoxic fluroxypyr acid. One unique metabolite was present in Flur-R that was not present in the J01-S metabolic profile. Gene sequence variant analysis specifically for auxin receptor and signaling proteins revealed the absence of non-synonymous mutations affecting auxin signaling and binding in candidate auxin target site genes, further supporting our hypothesis that non-target site metabolic degradation is contributing to fluroxypyr resistance in Flur-R.

A high diversity of non-target site resistance mechanisms to acetolactate-synthase (ALS) inhibiting herbicides has evolved within and among field populations of common ragweed (Ambrosia artemisiifolia L.)

BackgroundNon-target site resistance (NTSR) to herbicides is a polygenic trait that threatens the chemical control of agricultural weeds. NTSR involves differential regulation of plant secondary metabolism pathways, but its precise genetic determinisms remain fairly unclear. Full-transcriptome sequencing had previously been implemented to identify NTSR genes. However, this approach had generally been applied to a single weed population, limiting our insight into the diversity of NTSR mechanisms. Here, we sought to explore the diversity of NTSR mechanisms in common ragweed (Ambrosia artemisiifolia L.) by investigating six field populations from different French regions where NTSR to acetolactate-synthase-inhibiting herbicides had evolved.ResultsA de novo transcriptome assembly (51,242 contigs, 80.2% completeness) was generated as a reference to seek genes differentially expressed between sensitive and resistant plants from the six populations. Overall, 4,609 constitutively differentially expressed genes were identified, of which none were common to all populations, and only 197 were shared by several populations. Similarly, population-specific transcriptomic response was observed when investigating early herbicide response. Gene ontology enrichment analysis highlighted the involvement of stress response and regulatory pathways, before and after treatment. The expression of 121 candidate constitutive NTSR genes including CYP71, CYP72, CYP94, oxidoreductase, ABC transporters, gluco and glycosyltransferases was measured in 220 phenotyped plants. Differential expression was validated in at least one ragweed population for 28 candidate genes. We investigated whether expression patterns at some combinations of candidate genes could predict phenotype. Within populations, prediction accuracy decreased when applied to an additional, independent plant sampling. Overall, a wide variety of genes linked to NTSR was identified within and among ragweed populations, of which only a subset was captured in our experiments.ConclusionOur results highlight the complexity and the diversity of NTSR mechanisms that can evolve in a weed species in response to herbicide selective pressure. They strongly point to a non-redundant, population-specific evolution of NTSR to ALS inhibitors in ragweed. It also alerts on the potential of common ragweed for rapid adaptation to drastic environmental or human-driven selective pressures.

Comprehensive insights into herbicide resistance mechanisms in weeds: a synergistic integration of transcriptomic and metabolomic analyses.

Omics techniques, including genomics, transcriptomics, proteomics, and metabolomics have smoothed the researcher's ability to generate hypotheses and discover various agronomically relevant functions and mechanisms, as well as their implications and associations. With a significant increase in the number of cases with resistance to multiple herbicide modes of action, studies on herbicide resistance are currently one of the predominant areas of research within the field of weed science. High-throughput technologies have already started revolutionizing the current molecular weed biology studies. The evolution of herbicide resistance in weeds (particularly via non-target site resistance mechanism) is a perfect example of a complex, multi-pathway integration-induced response. To date, functional genomics, including transcriptomic and metabolomic studies have been used separately in herbicide resistance research, however there is a substantial lack of integrated approach. Hence, despite the ability of omics technologies to provide significant insights into the molecular functioning of weeds, using a single omics can sometimes be misleading. This mini-review will aim to discuss the current progress of transcriptome-based and metabolome-based approaches in herbicide resistance research, along with their systematic integration.

Sequence Characterization of Extra-Chromosomal Circular DNA Content in Multiple Blackgrass (Alopecurus myosuroides) Populations.

Alopecurus myosuroides (blackgrass) is a problematic weed of Western European winter wheat, and its success is largely due to widespread multiple-herbicide resistance. Previous analysis of F2 seed families derived from two distinct blackgrass populations exhibiting equivalent non-target site resistance (NTSR) phenotypes shows resistance is polygenic and evolves from standing genetic variation. Using a CIDER-seq pipeline, we show that herbicide-resistant (HR) and herbicide-sensitive (HS) F3 plants from these F2 seed families as well as the parent populations they were derived from carry extra-chromosomal circular DNA (eccDNA). We identify the similarities and differences in the coding structures within and between resistant and sensitive populations. Although the numbers and size of detected eccDNAs varied between the populations, comparisons between the HR and HS blackgrass populations identified shared and unique coding content, predicted genes, and functional protein domains. These include genes related to herbicide detoxification such as Cytochrome P450s, ATP-binding cassette transporters, and glutathione transferases including AmGSTF1. eccDNA content was mapped to the A. myosuroides reference genome, revealing genomic regions at the distal end of chromosome 5 and the near center of chromosomes 1 and 7 as regions with a high number of mapped eccDNA gene density. Mapping to 15 known herbicide-resistant QTL regions showed that the eccDNA coding sequences matched twelve, with four QTL matching HS coding sequences; only one region contained HR coding sequences. These findings establish that, like other pernicious weeds, blackgrass has eccDNAs that contain homologs of chromosomal genes, and these may contribute genetic heterogeneity and evolutionary innovation to rapidly adapt to abiotic stresses, including herbicide treatment.

Divergence in Glyphosate Susceptibility between Steinchisma laxum Populations Involves a Pro106Ser Mutation.

The characterization of the mechanisms conferring resistance to herbicides in weeds is essential for developing effective management programs. This study was focused on characterizing the resistance level and the main mechanisms that confer resistance to glyphosate in a resistant (R) Steinchisma laxum population collected in a Colombian rice field in 2020. The R population exhibited 11.2 times higher resistance compared to a susceptible (S) population. Non-target site resistance (NTSR) mechanisms that reduced absorption and impaired translocation and glyphosate metabolism were not involved in the resistance to glyphosate in the R population. Evaluating the target site resistance mechanisms by means of enzymatic activity assays and EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene sequencing, the mutation Pro106Ser was found in R plants of S. laxum. These findings are crucial for managing the spread of S. laxum resistance in Colombia. To effectively control S. laxum in the future, it is imperative that farmers use herbicides with different mechanisms of action in addition to glyphosate and adopt Integrate Management Programs to control weeds in rice fields of the central valleys of Colombia.

Target and non-target site mechanisms of fungicide resistance and their implications for the management of crop pathogens.

Fungicides are indispensable for high-quality crops, but the rapid emergence and evolution of fungicide resistance have become the most important issues in modern agriculture. Hence, the sustainability and profitability of agricultural production have been challenged due to the limited number of fungicide chemical classes. Resistance to site-specific fungicides has principally been linked to target and non-target site mechanisms. These mechanisms change the structure or expression level, affecting fungicide efficacy and resulting in different and varying resistance levels. This review provides background information about fungicide resistance mechanisms and their implications for developing anti-resistance strategies in plant pathogens. Here, our purpose was to review changes at the target and non-target sites of quinone outside inhibitor fungicides (QoIs), methyl-benzimidazole fungicides (MBCs), demethylation inhibitor fungicides (DMIs), and succinate dehydrogenase inhibitor fungicides (SDHIs) and to evaluate if they may also be associated with a fitness cost on crop pathogen populations. The current knowledge suggests that understanding fungicide resistance mechanisms can facilitate resistance monitoring and assist in developing anti-resistance strategies and new fungicide molecules to help solve this issue. This article is protected by copyright. All rights reserved.

Predicting the unpredictable: the regulatory nature and promiscuity of herbicide cross resistance.

The emergence of herbicide-resistant weeds is a significant threat to modern agriculture. Cross resistance, a phenomenon where resistance to one herbicide confers resistance to another, is a particular concern owing to its unpredictability. Nontarget-site (NTS) cross resistance is especially challenging to predict, as it arises from genes that encode enzymes that do not directly involve the herbicide target site and can affect multiple herbicides. Recent advancements in genomic and structural biology techniques could provide new venues for predicting NTS resistance in weed species. In this review, we present an overview of the latest approaches that could be used. We discuss the use of genomic and epigenomics techniques such as ATAC-seq and DAP-seq to identify transcription factors and cis-regulatory elements associated with resistance traits. Enzyme/protein structure prediction and docking analysis are discussed as an initial step for predicting herbicide binding affinities with key enzymes to identify candidates for subsequent in vitro validation. We also provide example analyses that can be deployed toward elucidating cross resistance and its regulatory patterns. Ultimately, our review provides important insights into the latest scientific advancements and potential directions for predicting and managing herbicide cross resistance in weeds. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Quizalofop resistance in weedy rice (Oryza sativa L.) is mainly conferred by an Ile1781Leu mutation

Weedy rice (Oryza sativa L.) is an economically important weed species in rice (Oryza sativa L.) cropping systems. Two weedy rice samples (acc7 and acc8) suspected to be resistant to quizalofop-ethyl (quizalofop) were collected in Arkansas. In this research, susceptibility to quizalofop and resistance mechanisms have been explored. Dose-response assays displayed a resistance index of 42- and 58-fold for the acc7 and acc8, respectively. Experiments with metabolism inhibitors demonstrated that NBD-Cl (4-chloro-7-nitrobenzofurazan) increased quizalofop efficacy slightly in acc8, whereas malathion did not improve effectiveness in resistant samples. Sequencing of the ACCase gene displayed an Ile1781Leu substitution in the resistant samples, like the mutation present in Provisia™ rice. In addition, an allele-specific PCR was developed to genotype the Ile1781Leu mutation. The gene copy number of ACCase showed similar values among samples. In the resistant plants, a KASP (Kompetitive Allele Specific PCR) assay to detect the ALSS653D (acetolactate synthase) and HIS1 (HPPD Inhibitor Sensitive 1) traits revealed that 37.5% of plants carried the ALSS653D trait, whereas 25% showed the HIS1 allele. In summary, a target-site mutation is the main resistance mechanism to quizalofop in weedy rice. Results also suggest the presence of herbicide metabolism (a non-target site resistance mechanism) mediated by glutathione-S-transferases (GSTs) in one resistant sample.