Succinate Dehydrogenase Inhibitor Research Articles

Comparative antioxidant and metabolomic analysis for the identification of differential response of mussel (Mytilus coruscus) to four succinate dehydrogenase inhibitor fungicides.

Succinate dehydrogenase inhibitor fungicides (SDHIs) are frequently detected in the marine environment. However, studies on the toxicity of SDHIs to marine organisms, Mytilus coruscus (M. coruscus), are poorly reported. Therefore, the antioxidant activities and metabolomic response of four SDHIs, namely, boscalid (BC), thifluzamide (TF), fluopyram (FO), and bixafen (BIX), to (M. coruscus), were comprehensively investigated. The antioxidant activity of BC and TF was significantly increased (p<0.05), whereas those of FO and BIX were significantly decreased. Furthermore, metabolite discriminations among M. coruscus to four SDHIs were illustrated by an untargeted metabolomics approach. A total of 52, 50, 93, and 129 differential metabolites were obtained for BC, TF, FO, and BIX. KEGG of the different metabolites show that the four SDHIs had differential effects on the metabolic pathways of M. coruscus. The current study demonstrated four SDHIs triggered glucose metabolism, lipid metabolism, tricarboxylic acid cycle, and oxidative phosphorylation processes and caused the disruption of nutrient and energy conversion processes in mussels. Finally, five biomarkers were screened by analyzing common differential metabolites that emerged from the four SDHI exposures, which could be used for risk assessment of marine ecosystem exposure to SDHIs. Our results demonstrated the use of metabolomics to understand the potential mechanisms of toxicity of four SDHIs to mussels and to identify potential targets for future targeted risk assessment.

Design and Synthesis of Novel Diphenyl Ether Carboxamide Derivatives To Control the Phytopathogenic Fungus Sclerotinia sclerotiorum.

Sclerotinia stem rot (SSR) caused by the phytopathogenic fungus Sclerotinia sclerotiorum has led to serious losses in the yields of oilseed rape and other crops every year. Here, we designed and synthesized a series of carboxamide derivatives containing a diphenyl ether skeleton by adopting the scaffold splicing strategy. From the results of the mycelium growth inhibition experiment, inhibition rates of compounds 4j and 4i showed more than 80% to control S. sclerotiorum at a dose of 50 μg/mL, which is close to that of the positive control (flubeneteram, 95%). Then, the results of a structure-activity relationship study showed that the benzyl scaffold was very important for antifungal activity and that introducing a halogen atom on the benzyl ring would improve antifungal activity. Furthermore, the results of an in vitro activity test suggested that these novel compounds can inhibit the activity of succinate dehydrogenase (SDH), and the binding mode of 4j with SDH was basically similar to that of the flutolanil derivative. Morphological observation of mycelium revealed that compound 4j could cause a damage on the mycelial morphology and cell structure of S. sclerotiorum, resulting in inhibition of the growth of mycelia. Furthermore, in vivo antifungal activity assessment of 4j displayed a good control of S. sclerotiorum (>97%) with a result similar to that of the positive control at a concentration of 200 mg/L. Thus, the diphenyl ether carboxamide skeleton is a new starting point for the discovery of new SDH inhibitors and is worthy of further development.

Anandamide and WIN 55212–2 Afford Protection in Rat Brain Mitochondria in a Toxic Model Induced by 3-Nitropropionic Acid: an In Vitro Study

Mitochondrial dysfunction plays a key role in the development of neurodegenerative disorders. In contrast, the regulation of the endocannabinoid system has been shown to promote neuroprotection in different neurotoxic paradigms. The existence of an active form of the cannabinoid receptor 1 (CB1R) in mitochondrial membranes (mitCB1R), which might exert its effects through the same signaling mechanisms as the cell membrane CB1R, has been shown to regulate mitochondrial activity. Although there is evidence suggesting that some cannabinoids may induce protective effects on isolated mitochondria, substantial evidence on the role of cannabinoids in mitochondria remains to be explored. In this work, we developed a toxic model of mitochondrial dysfunction induced by exposure of brain mitochondria to the succinate dehydrogenase inhibitor 3-nitropropionic acid (3-NP). Mitochondria were also pre-incubated with the endogenous agonist anandamide (AEA) and the synthetic CB1R agonist WIN 55212–2 to evaluate their protective effects. Mitochondrial reduction capacity, reactive oxygen species (ROS) formation, and mitochondrial swelling were assessed as toxic markers. While 3-NP decreased the mitochondrial reduction capacity and augmented mitochondrial ROS formation and swelling, both AEA and WIN 55212–2 ameliorated these toxic effects. To explore the possible involvement of mitCB1R activation on the protective effects of AEA and WIN 55212–2, mitochondria were also pre-incubated in the presence of the selective CB1R antagonist AM281, which completely reverted the protective effects of the cannabinoids to levels similar to those evoked by 3-NP. These results show partial protective effects of cannabinoids, suggesting that mitCB1R activation may be involved in the recovery of compromised mitochondrial activity, related to reduction of ROS formation and further prevention of mitochondrial swelling.

Succinate dehydrogenase inhibitors (SDHi): focus on mitotoxic pesticides

Succinate dehydrogenase inhibitors (SDHi): focus on mitotoxic pesticides

Abstract WMP12: Acid-Formulated Malonate Improves Neuroprotection Ischemia-Selective in a Mouse Model of Ischemic Stroke

Background: Malonate, a competitive inhibitor of succinate dehydrogenase, has shown much promise in ameliorating ischemia/reperfusion injury (IRI) in various diseases, including ischemic stroke. Its uptake via the monocarboxylate transporter 1 (MCT1) is enhanced by a decrease in local pH, enabling it to be preferentially taken up by ischemic tissue. We investigated whether an acid-formulated malonate could enhance uptake of malonate and, consequently, protection against stroke IRI. Methods: C57BL/6J mice were treated intravenously with either saline or malonate (640/320 mg/kg) at physiological (7.4) or low pH (6.0). Brain malonate levels were assessed by liquid chromatography-tandem mass spectrometry LC-MS/MS. For the transient middle cerebral artery occlusion (tMCAO) stroke model, mice were subjected to 30 mins ischaemia followed by either 2 hour reperfusion. Brain infarct size was assessed by TTC (2,3,5-triphenyl-2H-tetrazolium chloride) staining. Results: Malonate was acutely protective against stroke IRI with a reduction in brain infarct size from 21.98% to 6.57% after 2 hours of reperfusion. Malonate uptake into the brain in vivo dramatically increased when infused at pH 6 compared to neutral malonate. Furthermore, acid-formulation greatly enhanced the neuroprotective potency of malonate, enabling protection at a much lower dose compared to its non-acidic counterpart. Conclusions: Malonate is neuroprotective against stroke IRI. Its uptake via MCT1 and, ultimately its neuroprotective potency can be enhanced by acid formulation of the drug.

ROS-Suppression Nanoplatform Combined Activation of STAT3/Bcl-2 Pathway for Preventing Myocardial Infarction in Mice.

Myocardial infarction (MI) is the leading cause of death worldwide. The most effective way to treat myocardial infarction is to rescue ischemic cardiomyocytes. After an ischemic event, the overproduction of reactive oxygen species (ROS) is a key driver of myocardial injury. The produced ROS affects mitochondrial function and induces apoptosis in cardiomyocytes. This was accomplished by constructing platelet-membrane-encapsulated ROS-responsive drug-releasing nanoparticles (PMN@NIC-MalNPs) to deliver malonate and niclosamide (NIC). The results revealed that PMN@NIC-MalNPs degraded and released malonate and niclosamide in a high-level ROS microenvironment, effectively reducing the oxidative stress and apoptosis rate. By enhancing basal mitochondrial oxygen consumption rate (OCR), adenosine triphosphate (ATP) production, and spare respiratory capacity (SRC) in vitro, reduced the oxidative stress levels and restored mitochondrial function. In vivo studies revealed that the PMN@NIC-MalNPs improved cardiac dysfunction, inhibited succinate dehydrogenase (SDH) activity, increased ATP production, and reduced the myocardial infarct size in myocardial infarction model mice. Further, transcriptome analysis and Western blot revealed that PMN@NIC-MalNPs prevented apoptosis by activating the expressions of the signal transducer and activator of transcription 3 (STAT3) and Bcl-2, and inhibiting the expression of Bax. Thus, this study provides a novel therapeutic solution for treating myocardial infarction and predicting the viability of an antioxidant and antiapoptotic therapeutic solution in the treatment of myocardial injury.

Novel Pyrazole Acyl(thio)urea Derivatives Containing a Biphenyl Scaffold as Potential Succinate Dehydrogenase Inhibitors: Design, Synthesis, Fungicidal Activity, and SAR.

As part of a program to discover novel succinate dehydrogenase inhibitor fungicides, a series of new pyrazole acyl(thio)urea compounds containing a diphenyl motif were designed and synthesized. Their structures were confirmed by 1H NMR, HRMS, and single X-ray crystal diffraction analysis. Most of these compounds possessed excellent activity against 10 fungal plant pathogens at 50 μg mL-1, especially against Rhizoctonia solani, Alternaria solani, Sclerotinia sclerotiorum, Botrytis cinerea, and Cercospora arachidicola. Interestingly, compounds 3-(difluoromethyl)-1-methyl-N-((3',4',5'-trifluoro-[1,1'-biphenyl]-2-yl)carbamoyl)-1H-pyrazole-4-carboxamide (9b, EC50 = 0.97 ± 0.18 μg mL-1), 1,3-dimethyl-N-((3',4',5'-trifluoro-[1,1'-biphenyl]-2-yl)carbamoyl)-1H-pyrazole-4-carboxamide (9a, EC50 = 2.63 ± 0.41 μg mL-1), and N-((4'-chloro-[1,1'-biphenyl]-2-yl)carbamoyl)-1,3-dimethyl-1H-pyrazole-4-carboxamide (9g, EC50 = 1.31 ± 0.15 μg mL-1) exhibited activities against S. sclerotiorum that were better than the commercial fungicide bixafen (EC50 = 9.15 ± 0.05 μg mL-1) and similar to the positive control fluxapyroxad (EC50 = 0.71 ± 0.11 μg mL-1). These compounds were not significantly phytotoxic to monocotyledonous and dicotyledonous plants. Structure-activity relationships (SAR) are discussed by substituent effects/molecular docking, and density functional theory analysis indicated that these compounds are succinate dehydrogenase inhibitors.

A universal metabolite repair enzyme removes a strong inhibitor of the TCA cycle

A prevalent side-reaction of succinate dehydrogenase oxidizes malate to enol-oxaloacetate (OAA), a metabolically inactive form of OAA that is a strong inhibitor of succinate dehydrogenase. We purified from cow heart mitochondria an enzyme (OAT1) with OAA tautomerase (OAT) activity that converts enol-OAA to the physiological keto-OAA form, and determined that it belongs to the highly conserved and previously uncharacterized Fumarylacetoacetate_hydrolase_domain-containing protein family. From all three domains of life, heterologously expressed proteins were shown to have strong OAT activity, and ablating the OAT1 homolog caused significant growth defects. In Escherichia coli, expression of succinate dehydrogenase was necessary for OAT1-associated growth defects to occur, and ablating OAT1 caused a significant increase in acetate and other metabolites associated with anaerobic respiration. OAT1 increased the succinate dehydrogenase reaction rate by 35% in in vitro assays with physiological concentrations of both succinate and malate. Our results suggest that OAT1 is a universal metabolite repair enzyme that is required to maximize aerobic respiration efficiency by preventing succinate dehydrogenase inhibition.

Sensitivity of Meloidogyne incognita, Fusarium oxysporum f. sp. niveum, and Stagonosporopsis citrulli to Succinate Dehydrogenase Inhibitors Used for Control of Watermelon Diseases.

Watermelon is affected by diseases such as Fusarium wilt, gummy stem blight, and root-knot nematode (RKN). Succinate dehydrogenase inhibitors (SDHIs) with potential fungicide and nematicide activity provide the opportunity to control multiple diseases with one compound. In this study, we aimed to determine the sensitivity of Meloidogyne incognita race 4 (MI4), Fusarium oxysporum f. sp. niveum (FON), and Stagonosporopsis citrulli (SCIT) to existing SDHIs: benzovindiflupyr, fluopyram, cyclobutrifluram, and pydiflumetofen. All SDHIs had fungicidal activity against 19 SCIT isolates in mycelial growth assays, but isolates were most sensitive to pydiflumetofen (median EC50 = 0.41 μg/ml). Most of the 50 FON isolates tested were sensitive to cyclobutrifluram for mycelial growth (median EC50 = 4.04 μg/ml) and conidial germination (median EC50 = 0.2 μg/ml) assays but were not sensitive to fluopyram. MI4 was most sensitive to cyclobutrifluram for egg hatch (mean EC50 = 0.0019 μg/ml) and J2 motility (mean EC50 = 1.16 μg/ml) assays but was not sensitive to pydiflumetofen. Significant positive correlations between the sensitivity of SCIT (mycelial growth) and FON (mycelial growth and conidial germination) for cyclobutrifluram and benzovindiflupyr (SCIT r = 0.88; FON r = 0.7; P < 0.0001) and cyclobutrifluram and pydiflumetofen (SCIT r = 0.83; FON r = 0.67 and 0.77; P < 0.0001) indicate a potential for cross-resistance between these SDHIs for these fungal pathogens. Overall, results suggest that cyclobutrifluram may be used for managing RKN, whereas it should be used judiciously for Fusarium wilt of watermelon and gummy stem blight due to the existence of insensitive isolates to the fungicide.

Workflows for detecting fungicide resistance in net form and spot form net blotch pathogens.

Fungicide resistance in Pyrenophora teres f. maculata and P. teres f. teres has become an important disease management issue. Control of the associated barley foliar diseases, spot form and net form net blotch, respectively, relies on three major groups of fungicides, demethylation inhibitors (DMIs), succinate dehydrogenase inhibitors (SDHIs) and quinone outside inhibitors (QoIs). However, resistance has been reported for the DMI and SDHI fungicides in Australia. To enhance detection of different resistance levels, phenotyping and genotyping workflows were designed. The phenotyping workflow generated cultures directly from lesions and compared growth on discriminatory doses of tebuconazole (DMI) and fluxapyroxad (SDHI). Genotyping real-time polymerase chain reaction (PCR) assays were based on alleles associated with sensitivity or resistance to the DMI and SDHI fungicides. These workflows were applied to spot form and net form net blotch collections from 2019 consisting predominantly of P. teres f. teres from South Australia and P. teres f. maculata from Western Australia. For South Australia the Cyp51A L489-3 and SdhC-R134 alleles, associated with resistance to tebuconazole and fluxapyroxad, respectively, were the most prevalent. These alleles were frequently found in single isolates with dual resistance. This study also reports the first detection of a 134 base pair insertion located at position-66 (PtTi-6) in the Cyp51A promoter of P. teres f. maculata from South Australia. For Western Australia, the PtTi-1 insertion was the most common allele associated with resistance to tebuconazole. The workflow and PCR assays designed in this study have been demonstrated to efficiently screen P. teres collections for both phenotypic and genetic resistance to DMI and SDHI fungicides. The distribution of reduced sensitivity and resistance to DMI and SDHI fungicides varied between regions in south-western Australia, suggesting the emergence of resistance was impacted by both local pathogen populations and disease management programmes. The knowledge of fungicide resistance in regional P. teres collections will be important for informing appropriate management strategies. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Resistance risk, resistance mechanism and the effect on DON production of a new SDHI fungicide cyclobutrifluram in Fusarium graminearum

Fusarium head blight in wheat is caused by Fusarium graminearum, resulting in significant yield losses and grain contamination with deoxynivalenol (DON), which poses a potential threat to animal health. Cyclobutrifluram, a newly developed succinate dehydrogenase inhibitor, has shown excellent inhibition of Fusarium spp. However, the resistance risk of F. graminearum to cyclobutrifluram and the molecular mechanism of resistance have not been determined. In this study, we established the average EC50 of a range of F. graminearum isolates to cyclobutrifluram to be 0.0110 μg/mL. Six cyclobutrifluram-resistant mutants were obtained using fungicide adaptation. All mutants exhibited impaired fitness relative to their parental isolates. This was evident from measurements of mycelial growth, conidiation, conidial germination, virulence, and DON production. Interestingly, cyclobutrifluram did not seem to affect the DON production of either the sensitive isolates or the resistant mutants. Furthermore, a positive cross-resistance was observed between cyclobutrifluram and pydiflumetofen. These findings suggest that F. graminearum carries a moderate to high risk of developing resistance to cyclobutrifluram. Additionally, point mutations H248Y in FgSdhB and A73V in FgSdhC1 of F. graminearum were observed in the cyclobutrifluram-resistant mutants. Finally, an overexpression transformation assay and molecular docking indicated that FgSdhBH248Y or FgSdhC1A73V could confer resistance of F. graminearum to cyclobutrifluram.

Design, synthesis, antifungal activity and molecular docking of novel pyrazole-4-carboxamides containing tertiary alcohol and difluoromethyl moiety as potential succinate dehydrogenase inhibitors.

Resistance problems with the long-term and frequent use of existing fungicides, and the lack of structure diversity of traditional pyrazole-4-carboxamide succinate dehydrogenase inhibitors, it is highly required to design and develop new fungicides to address the resistance issue. Different from previous pyrazole-4-carboxamide succinate dehydrogenase inhibitors by breaking the norm of difluoromethyl at the C-3 position of pyrazole and introducing a tertiary alcohol group at the C-3 position, 27 novel pyrazole-4-carboxamide derivatives were designed, synthesized and characterized by proton (1 H) nuclear magnetic resonance (NMR), carbon-13 (13 C) NMR, fluorine-19 (19 F) NMR and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). The crystal structures of compounds A14 and C5 were analyzed by single crystal X-ray diffraction. Their in vitro antifungal activities were evaluated against phytopathogen Fusarium graminearum, Botrytis cinerea, Phytophthora capsica, Sclerotinia sclerotiorum, Thanatephorus cucumeris. The results displayed that most of them exhibited significant antifungal activities against S. sclerotiorum at 50 mg/L, the half maximal effective concentration (EC50 ) data of A8 and A14 were 3.96 and 2.52 mg/L, respectively. Their in vivo antifungal activities were evaluated against Pseudoperonospora cubensis, Puccinia sorghi Schw, Colletotrichum gloeosporioides, F. graminearum, Erysiphe graminis, Thanatephorus cucumeris, the control efficacies of A6, B3, C3, and C6 against E. graminis reached 100% at a concentration of 400 mg/L. The molecular docking results showed that the binding mode of the target compounds containing tertiary alcohols were similar to that of fluxapyroxad in succinate dehydrogenase. In addition, tertiary alcohols were involved in the formation of hydrogen bonds. The excellent in vitro and in vivo inhibitory activities of novel pyrazole-4-carboxamide derivatives against succinate dehydrogenase were reported for the first time, and they could be used as the potential lead compounds. © 2023 Society of Chemical Industry.

The influence of carbon dioxide on cerebral metabolism and oxygen consumption: combining multimodal monitoring with dynamic systems modelling.

Hypercapnia increases cerebral blood flow. The effects on cerebral metabolism remain incompletely understood although studies show an oxidation of cytochrome c oxidase, Complex IV of the mitochondrial respiratory chain. Systems modelling was combined with previously published non-invasive measurements of cerebral tissue oxygenation, cerebral blood flow, and cytochrome c oxidase redox state to evaluate any metabolic effects of hypercapnia. Cerebral tissue oxygen saturation and cytochrome oxidase redox state were measured with broadband near infrared spectroscopy and cerebral blood flow velocity with transcranial Doppler ultrasound. Data collected during 5-min hypercapnia in awake human volunteers were analysed using a Fick model to determine changes in brain oxygen consumption and a mathematical model of cerebral hemodynamics and metabolism (BrainSignals) to inform on mechanisms. Either a decrease in metabolic substrate supply or an increase in metabolic demand modelled the cytochrome oxidation in hypercapnia. However, only the decrease in substrate supply explained both the enzyme redox state changes and the Fick-calculated drop in brain oxygen consumption. These modelled outputs are consistent with previous reports of CO2 inhibition of mitochondrial succinate dehydrogenase and isocitrate dehydrogenase. Hypercapnia may have physiologically significant effects suppressing oxidative metabolism in humans and perturbing mitochondrial signalling pathways in health and disease.

Inhibitory activity to Fusarium spp. and control potential for wheat Fusarium crown rot of a novel succinate dehydrogenase inhibitor cyclobutrifluram.

Wheat Fusarium crown rot (FCR) is a serious problem primarily caused by Fusarium pseudograminearum, a pathogenic agent known to produce mycotoxins, including deoxynivalenol (DON). Cyclobutrifluram, a novel succinate dehydrogenase inhibitor devised by Syngenta, has immense potential to control both nematodes and Fusarium diseases. However, its efficacy in combating Fusarium species, its ability to prevent and reverse the detrimental effects of FCR, and its impact on the production of DON by F. pseudograminearum are yet to be fully ascertained. Cyclobutrifluram exhibited substantial inhibitory activity against Fusarium species, with half-maximal effective concentration values ranging from 0.0021-0.0647 μg mL-1 . It demonstrated significant inhibitory activity toward three developmental stages of F. pseudograminearum, F. graminearum and F. asiaticum. Furthermore, cyclobutrifluram showed both protective and curative activities against FCR and was rapidly absorbed by roots and transported to wheat stems and leaves. Cyclobutrifluram could also decrease DON production by F. pseudograminearum. This investigation has revealed the potential of cyclobutrifluram as a formidable candidate fungicide, particularly in its ability to effectively combat FCR and other Fusarium-related ailments. This novel compound has exceptional pathogen-fighting capabilities, coupled with remarkable systemic translocation properties and a notable ability to reduce the production of DON. © 2023 Society of Chemical Industry.

Protective Role of MAVS Signaling for Murine Lipopolysaccharide-Induced Acute Kidney Injury.

Despite treatment advances, acute kidney injury (AKI)-related mortality rates are still high in hospitalized adults, often due to sepsis. Sepsis and AKI could synergistically worsen the outcomes of critically ill patients. TLR4 signaling and mitochondrial antiviral signaling protein (MAVS) signaling are innate immune responses essential in kidney diseases, but their involvement in sepsis-associated AKI (SA-AKI) remains unclear. We studied the role of MAVS in kidney injury related to the TLR4 signaling pathway using a murine LPS-induced AKI model in wild-type and MAVS-knockout mice. We confirmed the importance of M1 macrophage in SA-AKI through invivo assessment of inflammatory responses. The TLR4 signaling pathway was upregulated in activated bone marrow-derived macrophages, in which MAVS helped maintain the LPS-suppressed TLR4 mRNA level. MAVS regulated redox homeostasis via NADPH oxidase Nox2 and mitochondrial reverse electron transport in macrophages to alleviate the TLR4 signaling response to LPS. Hypoxia-inducible factor 1α (HIF-1α) and AP-1 were key regulators of TLR4 transcription and connected MAVS-dependent reactive oxygen species signaling with the TLR4 pathway. Inhibition of succinate dehydrogenase could partly reduce inflammation in LPS-treated bone marrow-derived macrophages without MAVS. These findings highlight the renoprotective role of MAVS in LPS-induced AKI by regulating reactive oxygen species generation-related genes and maintaining redox balance. Controlling redox homeostasis through MAVS signaling may be a promising therapy for SA-AKI.

Activity of fungicide cyclobutrifluram against Fusarium fujikuroi and mechanism of the pathogen resistance associated with point mutations in FfSdhB, FfSdhC2 and FfSdhD

Rice bakanae disease (RBD) is a devastating plant disease caused by Fusarium fujikuroi. This study aimed to evaluate the potential of cyclobutrifluram, a novel succinate dehydrogenase inhibitor (SDHI), to control RBD, and determine the risk and mechanism of resistance to cyclobutrifluram in F. fujikuroi. In vitro experiments showed that cyclobutrifluram significantly inhibited mycelial growth and spore germination, and altered the morphology of mycelia and conidia. Treatment with cyclobutrifluram significantly decreased mycotoxin production and increased cell membrane permeability in F. fujikuroi. The baseline sensitivity of 72 F. fujikuroi isolates to cyclobutrifluram was determined using mycelial growth and spore germination inhibition assays, which revealed EC50 values of 0.0114 – 0.1304 μg mL-1 and 0.0012 – 0.016 μg mL-1, with mean EC50 values of 0.0410 ± 0.0470 μg mL-1 and 0.0038 ± 0.0015 μg mL-1, respectively. Pot experiments demonstrated that the protective effect of cyclobutrifluram against F. fujikuroi was more significant than that of phenamacril and azoxystrobin, indicating that cyclobutrifluram is a promising antifungal agent for the control of RBD. Six cyclobutrifluram-resistant mutants of F. fujikuroi were obtained via fungicide adaptation. Moreover, these mutants exhibited weaker fitness than their parental isolate and positive cross-resistance with other SDHI fungicides, including pydiflumetofen and penflufen; however, no cross-resistance was detected with other classes of fungicides, including phenamacril, fludioxonil, prochloraz, or azoxystrobin. These results indicated that the resistance risk of F. fujikuroi to cyclobutrifluram might be moderate. Sequencing analysis revealed that mutations, including H248D in FfSdhB, A83V in FfSdhC2, and S106F and E166K in FfSdhD, contributed to resistance, which was confirmed by molecular docking and homologous replacement experiments. The results suggest a high potential for cyclobutrifluram to control RBD and a moderate resistance risk of F. fujikuroi to cyclobutrifluram, which are meaningful findings for the scientific application of cyclobutrifluram.

Evaluation of foliar fungicides for frogeye leaf spot control and yield protection in soybean in Arkansas

The efficacy of fifteen foliar fungicides to control frogeye leaf spot (caused by Cercospora sojina K. Hara) and protect soybean grain yield was investigated over three years (2014–2016) in two field experiments. Experiments were divided into two fungicide groups: premix fungicides, which included combinations of quinone outside inhibitors (QoI), demethylation inhibitors (DMI), succinate dehydrogenase inhibitors (SDHI), or methyl benzimidazole carbamates (MBC), and solo fungicides, all DMI fungicides. Fungicides were applied once at the full pod (R4) in 2014 and 2015 and at the beginning seed (R5) growth stage in 2016. A very susceptible frogeye leaf spot cultivar, Armor 48R40, was used. Frogeye leaf spot severity at fungicide application timing average 1.0, 0.5, and 8.0% in 2014, 2015, and 2016, respectively. Final disease severity averaged 21.7, 14.5, and 15.1% in 2014, 2015, and 2016, respectively on the non-treated control. Azoxystrobin provided no disease control, suggesting the presence of QoI-resistant C. sojina. Three fungicides: azoxystrobin + difenoconazole, flutriafol, and thiophanate-methyl + tebuconazole applied at R4 provided effective disease control compared to the non-treated control. Fungicides applied at R5 provided no disease control. No fungicide provided significant grain yield protection in either experiment. Overall, the average yield protection trend by fungicides applied at R4 and R5 was 6.8 and 3.0%, respectively compared to the non-treated control. These data suggest that although foliar fungicides can provide effective frogeye leaf spot control, yield protection may be limited when applied at the R4 growth stage, particularly when disease severity exceeds 0.5% on a very susceptible soybean cultivar.

Anti-fungal activity of a novel succinate dehydrogenase inhibitor pydiflumetofen against Bipolaris maydis

Southern corn leaf blight (SCLB) is a disease caused by Bipolaris maydis. Pydiflumetofen is a novel succinate dehydrogenase inhibitor (SDHI) fungicide. However, its inhibitory activity against B. maydis has not been investigated in depth. In this study, mycelial growth rate and spore germination methods were used to establish a baseline for the sensitivity of 102 B. maydis strains collected from five regions of China to pydiflumetofen. The results showed that pydiflumetofen exhibited strong inhibitory activity against B. maydis. The EC50 values ranged from 0.0292 to 0.5207 μg/mL and from 0.0115 to 0.4883 μg/mL, with the average EC50 values of 0.2050 ± 0.1779 μg/mL and 0.1858 ± 0.0994 μg/mL for inhibition of mycelial growth and spore germination, respectively. After treatment with pydiflumetofen, the apical branching of mycelia increased significantly, and morphological changes such as twisting, deformation, rupture, and shriveling of mycelia and spores were observed. In addition, it significantly increased cell membrane permeability and decreased succinate dehydrogenase (SDH) activity and adenosine triphosphate (ATP) content. Moreover, the SDH gene expressions were changed, in which MbSdhB, MbSdhC and MbSdhD expressions were significantly upregulated, except for MbSdhA expression, which was significantly downregulated. In detached leaf experiments, pydiflumetofen showed strong protective and curative effects against B. maydis, superior to the same concentration of prochloraz and pyraclostrobin, and its protective effect was better than its curative effect. The field trials showed that the control efficacy of pydiflumetofen at 225 g/hm2 was >70% and its control efficacy at 300 g/hm2 reached 81.77%, which was significantly higher than that of pyraclostrobin and epoxiconazole at the same dosage. After 1:1 mixing of pydiflumetofen with the above control agents, the control efficacies of these mixtures at the same dosage increased compared to the use of a single agent. All the above results demonstrated that pydiflumetofen exhibits excellent inhibitory activity against B. maydis and good control of SCLB, suggesting that it could be used as an alternative fungicide for the control of SCLB.

Design, Synthesis, Nematicidal Activity, and Mechanism of Novel Amide Derivatives Containing an 1,2,4-Oxadiazole Moiety.

To discover new nematicides, a series of novel amide derivatives containing 1,2,4-oxadiazole were designed and synthesized. Several compounds showed excellent nematicidal activity. The LC50 values of compounds A7, A18, and A20-A22 against pine wood nematode (Bursaphelenchus xylophilus), rice stem nematode (Aphelenchoides besseyi), and sweet potato stem nematode (Ditylenchus destructor) were 1.39-3.09 mg/L, which were significantly better than the control nematicide tioxazafen (106, 49.0, and 75.0 mg/L, respectively). Compound A7 had an outstanding inhibitory effect on nematode feeding, reproductive ability, and egg hatching. Compound A7 effectively promoted the oxidative stress of nematodes and caused intestinal damage to nematodes. Compound A7 significantly inhibited the activity of succinate dehydrogenase (SDH) in nematodes, leading to blockage of electron transfer in the respiratory chain and thereby hindering the synthesis of adenosine triphosphate (ATP), which consequently affects the entire oxidative phosphorylation process to finally cause nematode death. Therefore, compound A7 can be used as a potential SDH inhibitor in nematicide applications.

Suppression of Leaf Spot Disease in Peanut (Arachis hypogaea) with Chlorothalonil, Copper Salts of Fatty Acid Rosins, and Microionized Sulfur

Concern over evolved resistance to fungicides that are quinone outside inhibitors (QOI), demethylation inhibitors (DMI), and succinate dehydrogenase inhibitors (SDHI) and possible restrictions on the use of the multi-site fungicide chlorothalonil for resistance management have increased the need to develop alternatives to current fungicide programs designed to protect peanut (Arachis hypogaea L.) from late leaf spot disease [caused by Nothopassalora personata (Berk. &amp; M.A. Curtis) U. Braun, C. Nakash., Videira &amp; Crous]. Research was conducted in North Carolina to determine the effectiveness of copper salts of fatty acid rosins and microionized sulfur in protecting peanut yield from canopy defoliation caused by late leaf spot disease. In one experiment, chlorothalonil was more effective in protecting peanut from leaf spot disease than copper salts of fatty acid rosins when these fungicides were applied five times on 14-day intervals during the cropping cycle when the pathogen was active. Chlorothalonil decreased defoliation caused by late leaf spot disease when co-applied with a diverse fungicide program consisting of prothioconazole plus tebuconazole, azoxystrobin, and pyraclostrobin compared with these fungicides without chlorothalonil. Copper salts of fatty acid rosins did not affect defoliation with the diverse fungicide program. In a second experiment, defoliation was similar when azoxystrobin or prothioconazole plus tebuconazole were applied alone or with microionized sulfur. Microionized sulfur provided similar protection from canopy defoliation compared with the more diverse fungicide programs.