Succinate Dehydrogenase Inhibitor Research Articles

Discovery of New Benzohydrazide Derivatives Containing 4-Aminoquinazoline as Effective Agricultural Fungicides, the Related Mechanistic Study, and Safety Assessment.

A total of 38 new benzohydrazide derivatives bearing the 4-aminoquinazoline moiety were designed and synthesized based on the active subunit combination approach and tested in detail for their inhibition activities against eight agricultural phytopathogenic fungi. The bioassay results indicated that many of the synthesized compounds exhibited extraordinary fungicidal activities in vitro against the tested fungi. For example, compounds A5, A6, A11, and A17 had EC50 (half-maximal effective concentration) values of 0.66, 0.71, 0.40, and 0.42 μg/mL against Colletotrichum gloeosporioides, respectively, comparable to that of boscalid (0.36 μg/mL) and much superior to that of carbendazim (6.96 μg/mL). Of particular importance was that compound A6 with a 3,4-difluorophenyl group was found to possess good broad-spectrum antifungal effects, with EC50 values ranging from 0.63 to 3.82 μg/mL against the tested eight fungi. In vivo antifungal assays also revealed that compound A6 had good curative and protective efficacies of 72.6% and 78.9% at 200 μg/mL against Rhizoctonia solani-caused rice sheath blight, higher than those of boscalid (70.7 and 65.2%, respectively). Moreover, the mechanism-of-action studies revealed that compound A6 disrupted the cell membrane integrity of R. solani, as proved by relative conductivity measurements, leakage of cellular contents, fluorescence microscopy, and scanning electron microscopy observations. Significantly, this compound also exhibited an effective inhibition of succinate dehydrogenase (SDH) from R. solani (half-maximal inhibitory concentration/IC50 = 11.02 μM), slightly weaker than that of the SDH inhibitor boscalid (5.17 μM). Further molecular docking analysis revealed that compound A6 could form strong interactions with the key residues of SDH enzyme via hydrogen bond, electrostatic, and π-cation interactions, holding promise for acting as new fungicide leads targeting SDH. Finally, the safety assessments indicated that compound A6 was safe for rice and honeybees.

Ecotoxicological impact of succinate dehydrogenase inhibitor (SDHI) fungicides on non-targeted organisms: a review.

As the global population continues to grow, the use of pesticides to increase food production is projected to escalate. Pesticides are critical in plant protection, offering a powerful defense against fungal diseases such as apple scab, leaf spot, sclerotinia rot, damping off, sheath blight, and root rot, which threaten crops like cereals, corn, cotton, soybean, sugarcane, tuberous vegetables, and ornamentals. Succinate Dehydrogenase Inhibitor (SDHI) fungicides represent a novel class essential for controlling fungal pathogens and bolstering food security. However, the impact of SDHIs on non-target organisms, including freshwater and terrestrial invertebrates, crustaceans, and oligochaetes, remains insufficiently understood. Empirical studies indicate that SDHIs can induce mortality, mitochondrial dysfunction, oxidative stress, and developmental delays in non-target organims. Additionally, the environmental persistence of these compounds raises concerns about their potential for ecological disruption. The effects of SDHIs on pollinating species and the possible transgenerational transmission of harmful effects warrant further investigation. Comprehensive transcriptomic analyses are necessary to elucidate the molecular disturbances and adverse outcome pathways triggered by SDHIs. Furthermore, there are emerging concerns about the endocrine-disrupting potential of SDHIs in aquatic organisms. For the first time, this review aims to synthesize existing knowledge on the ecotoxicological impacts of SDHIs on non-target organisms and identify critical research directions to address the ecological challenges posed by their use.

Synthesis, antifungal activity, and molecular simulation study of nootkatone-based thiazole-hydrazone compounds as novel succinate dehydrogenase inhibitor.

Plant diseases cause huge losses in agriculture worldwide every year, but the prolonged use of current commercial fungicides has led to the development of resistance in plant pathogenic fungi. Therefore, there is an urgent need to develop new, efficient, and green fungicides. Twenty-three nootkatone-based thiazole-hydrazone compounds were designed, synthesized, and characterized by Fourier-transform infrared (FTIR), proton (1H) nuclear magnetic resonance (NMR), carbon-13 (13C) NMR, and high-resolution mass spectrometry (HRMS). The antifungal activities results showed that all the target compounds displayed certain antifungal activity against eight tested fungi. Among them, target compounds 3a (88.7%), 3b (92.5%), 3d (88.7%), 3f (84.9%), 3j (88.7%), and 3l (92.5%) were comparable or superior to the positive control boscalid (88.7%) in their inhibitory activities against Physalospora piricola. Meanwhile, target compound 3l had half maximal effective concentration (EC50) values of 18.0172, 18.8236, 16.5914, 18.5044, and 16.5660 μg/mL against Fusarium oxysporum f. sp. cucumerinum, Alternaria solani, Gibberella zeae, Bipolaris maydis, and Colleterichum orbicalare, respectively, exhibiting outstanding and broad-spectrum fungicidal activity. Moreover, a three-dimensional quantitative structure-activity relationship (3D-QSAR) study was carried out to investigate the relationship between the molecular structures of target compounds 3a-3w and their antifungal activity. Furthermore, the target compound 3l [half maximal inhibitory concentration (IC50) = 4.936 μmol/L] showed significantly better inhibitory activity against succinate dehydrogenase (SDH) than boscalid (IC50 = 6.631 μmol/L). The possible binding mode between target compound 3l and homology-modeling built SDH, was also explored by molecular docking. Target compound 3l deserved further study as the promising candidate for the development of novel SDH inhibitor. © 2025 Society of Chemical Industry.

Fluopyram analogues containing an indole moiety: synthesis, biological activity and molecular docking study.

Succinate dehydrogenase (SDH) has been identified as one of the ideal targets for the development of novel nematicides. However, the resistance of nematodes to fluopyram, one of the commercialized SDH inhibitors, is becoming a growing concern. Since expanding the structural diversity around an active scaffold is a useful strategy for drug development, herein a series of fluopyram analogues with a broad, biologically relevant indole moiety were synthesized and evaluated for nematicidal activity against C. elegans. Fifty-six novel target compounds were synthesized and characterized by 1H NMR, 13C NMR, and HRMS. The bioscreen results revealed that a few compounds such as C16 and D21 with LC50/72h values of 8.65mg/L and 6.83mg/L, respectively, showed compatible activity to that of the commercial nematicide tioxazafen (LC50/72h = 5.98mg/L). Molecular docking indicated that these compounds could effectively bind to the active site of SDH by forming hydrogen bonds with Trp215 and Tyr96, and causing a cation-π interaction with Arg74.The work suggests that indole-containing derivatives may represent a promising template for the development of new nematicides.

Fungicide Sensitivity and Nontarget 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 µg ml-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, the EC50 of the isolates did not differ significantly among the years of collection (P > 0.05), and their single discriminatory concentrations were identified as 0.1 µg ml-1. This is the first study to establish nontarget 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 the future.

Inhibition of Mitochondrial Succinate Dehydrogenase with Dimethyl Malonate Promotes M2 Macrophage Polarization by Enhancing STAT6 Activation.

Macrophages exhibit diverse phenotypes depending on environment status, which contribute to physiological and pathological processes of immunological diseases, including sepsis, asthma, multiple sclerosis and colitis. The alternative activation of macrophages is tightly regulated to avoid excessive activation and damage of tissues and organs. Certain works characterized that succinate dehydrogenase (SDH) altered function of macrophages and promoted inflammatory response in M1 macrophages via mitochondrial reactive oxygen species (ROS). However, the effect of succinate dehydrogenase on M2 macrophage polarization remains incompletely understood. We employed dimethyl malonate (DMM) to inhibit succinate dehydrogenase activity and took use of RNA-seq to analyze the changes of inflammatory response of LPS-activated M1 macrophages or IL 4-activated M2 macrophages. Our data revealed that inhibition of SDH with DMM increased expression of M2 macrophages-associated signature genes, including Arg1, Ym1 and Mrc1. Consistent with previous work, we also observed that inhibition of SDH decreased the expression of IL-1β and enhanced the levels of IL-10 in M1 macrophages. Additionally, inhibition of SDH with DMM inhibited the production of chemokines, such as Cxcl3, Cxcl12, Ccl20 and Ccl9. DMM also amplified the M2 macrophages-related signature genes in IL-13-activated M2 macrophages. Mechanistic studies revealed that DMM promoted M2 macrophages polarization through mitochondrial ROS dependent STAT6 activation. Blocking ROS with mitoTEMPO or inhibiting STAT6 activation with ruxolitinib abrogated the promotion effect of DMM on M2 macrophages. Finally, dimethyl malonate treatment promoted peritoneal M2 macrophages differentiation and exacerbated OVA-induced allergy asthma in vivo. Collectively, we identified SDH as a braker to suppress M2 macrophage polarization via mitochondrial ROS, suggesting a novel strategy to treatment of M2 macrophages-mediated inflammatory diseases.

Synthesis and Fungicidal Activities of Coumarin Derivatives as Succinate Dehydrogenase Inhibitors.

Succinate dehydrogenase inhibitors (SDHIs) have been developed to the fastest growing family of fungicides. To develop novel succinate dehydrogenase (SDH) inhibitors, 27 novel non-amides coumarin derivatives were designed, synthesized, and characterized. The bioassay revealed that most of the target compounds exhibited significant antifungal activity against Botrytis cinerea in vitro. Notably, compounds 1a and 2c with EC50 values of 0.92 and 0.52µg/mL, respectively, which were better than that of positive control chlorothalonil (EC50=3.14µg/mL). Moreover, in vivo antifungal assay results showed that compound 2c could observably inhibit the growth of B. cinerea on Kuerla pears with remarkable protective at a dosage of 200µg/mL. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigation indicated that compound 2c significantly damaged the cell structures of B. cinerea mycelium. Three-dimensional quantitative structure-activity relationship (3D-QSAR) models were analyzed for structure-activity relationships of all target compounds. Furthermore, molecular docking revealed that compound 2c was able to bind closely to the receptor protein of SDH. Enzyme activity analysis also further verified its inhibitory effect. These results demonstrated that compound 2c may be potential candidate for novel SDH inhibitors, and these results afforded further valuable reference for SDHIs discovery.

Fluopyram SDHI pesticide alters fish physiology and behaviour despite low in vitro effects on mitochondria

Pollution from pesticides is an increasing concern for human health and biodiversity conservation. However, there is lack of knowledge about some emerging molecules such as SDHI fungicides (succinate dehydrogenase inhibitors) that are widely used but potentially highly toxic for vertebrates. Boscalid, fluopyram, and bixafen are 3 frequent SDHI molecules commonly detected in surface waters, which may pose risks to aquatic species. This study aimed to (1) test the in vitro effects of SDHI on mitochondrial activities (inhibition of succinate dehydrogenase SDH, also named respiratory chain complex II) and (2) assess the in vivo effects of sublethal SDHI concentrations on fish physiology and behaviour over 96 hours of exposure, using Carassius auratus fish as a model species. Results show that bixafen and boscalid inhibited complex II activities in vitro as expected (bixafen > boscalid), while fluopyram had no in vitro effects. In contrast, in vivo studies showed that fluopyram strongly altered fish behaviour (enhanced activity, social and feeding behaviours), likely explained by reduced AChE enzymatic activity. In addition, fluopyram increased muscle lipid content, suggesting metabolic disruption. These findings raise serious concern about the toxic effects of SDHI pesticides, especially fluopyram, although its underpinning molecular mechanisms remain to be explored. We thus encourage further research on the long-term impacts of SDHI pesticides to improve existing regulation and prevent adverse effects on wildlife.

Analysis of the stereoselective fate and toxicity of penflufen in the water-sediment system for risk reduction

Chiral succinate dehydrogenase inhibitor (SDHI) fungicides are widely used in agricultural production, but there is insufficient research on their environmental risk in water–sediment ecosystems. Here, the stereoselective fate and toxic effects of the chiral SDHI fungicide, penflufen, in the water–sediment system were investigated. The results showed that S-penflufen is more persistent in water, sediment, and zebrafish. Additionally, the sorption coefficient (Koc) in sediment and uptake rate constant (Ku) in zebrafish of S-penflufen were higher than those of R-penflufen. The acute toxicity of S-penflufen to zebrafish, Daphnia magna and Chironomus kiiensis were 32-, 6.1-, and 8.9-fold higher than those of R-penflufen. The AlphaFold2 and molecular docking results showed that S-penflufen had stronger binding capability with SDH in the three water–sediment organisms than R-penflufen. Therefore, S-penflufen induced stronger sub-chronic toxic effects on zebrafish than R-penflufen, even at 0.05 mg/L. The results of multi-omics analysis showed that S-penflufen affected the tricarboxylic acid cycle in zebrafish and induced antioxidant, detoxification, and immune system responses, ultimately affecting zebrafish metabolic processes and cellular function. The overall results indicate that S-penflufen has a higher risk in water–sediment systems. Moreover, combining multi-omics and AlphaFold2 techniques facilitates the elucidation of the molecular mechanism of the stereoselective toxic effects of chiral pesticides.

A systematic workflow of data mining confirms widespread ecological risks of SDHIs fungicides contamination in aquatic environment

Succinate dehydrogenase inhibitors (SDHIs) are widely utilized fungicides that have been detected in various environments, raising significant concerns regarding their toxicity to aquatic organisms. A comprehensive analysis of SDHIs contamination and associated ecological risks has been challenging due to scattered data and varying scale. This study consolidated residue data from 194 aquatic environments across six regions, up to June 2024, providing an overview of SDHIs distribution and conducting a global-scale aquatic ecological risk assessment. We analyzed 20 SDHIs, with boscalid, fluopyram, flutolanil, fluxapyroxad, mepronil, and thifluzamide being the most frequently detected across Asia, Europe, North America, South America, Africa, and Australia. The concentrations and types of SDHIs varied significantly among continents, with data sourced from water, sediment and aquatic organisms. Utilizing a web-based Interspecies Correlation Estimation-Species Sensitivity Distribution (ICE-SSD) model, we identified substantial sensitivity differences among species, with benzovindiflupyr showing the lowest LC50 of 3.5 μg/L, indicating a high risk when concentrations exceed 0.035 μg/L (Maximum Acceptable Concentration, MAC). Risk quotient (RQ) values revealed that flutolanil posed high risks to eight aquatic ecosystems and medium risks to five, while boscalid presented medium risk to one ecosystem. Our findings also demonstrated a significant correlation between the aquatic ecotoxicity of SDHIs and their characteristics (log Kow, solubility, and pKa). Collectively, we advocate for the restricted use of SDHIs and emphasize the necessity for further evaluation of their environmental behavior and integrated risks within the “One Health” framework.

Comprehensive Overview of the Amide Linker Modification in the Succinate Dehydrogenase Inhibitors.

Succinate dehydrogenase inhibitors (SDHIs) have become one of the most important classes of agrochemical fungicides. According to the data from FRAC, the resistance risk for SDHIs had reached up to medium and even to high. In general, the chemical structure of SDHIs mainly contained three fragments: an acid core, a hydrophobic tail, and an amide linker, corresponding to three modification directions for each fragment. Among them, amide linker modification (ALM) has become a research hotspot for the design of novel SDHIs fungicides in recent years. We presented here a detailed review on the ALM strategy in the past decade, and some of them had entered the market. According to their chemical structures, ALM strategy were classified into four parts: (1) linked aliphatic chain between amide bond and hydrophobic tail, (2) introducing substituents to replacing hydrogen atom in the amide bond, (3) reverse extending the amide linker, and (4) changed with other bioisosteres. Moreover, the structure-activity relationship and the interaction mechanism of ALM-SDHI with SDH were discussed. This review aims to provide a global perspective on research and development of novel SDHIs, as well as suggestions for food safety management.

Mitochondrial dysfunction induced in human hepatic HepG2 cells exposed to the fungicide kresoxim-methyl and to a mixture kresoxim-methyl/boscalid

ABSTRACT The fungicides strobilurins and succinate dehydrogenase inhibitors (SDHIs) are blockers of the electron transport chain (ETC) in fungi. Here, we show that the exposure for 24 h to kresoxym-methyl, a fungicide from the class of strobilurins, alters the mitochondrial respiration in human HepG2 hepatocytes. In addition, we demonstrate an increase in production of mitochondrial superoxide radical anion, a reduction in ATP level, a decrease in the ratio reduced/oxidized glutathione and a decrease in cell viability (assessed by the LDH assay, Presto Blue assay, and Crystal Violet assay). As kresoxym-methyl is associated to boscalid (SDHI) in commercial formulations, we analyzed a potential exacerbation of the induced mitochondrial dysfunction for this combination. For the highest dose at which kresoxym-methyl (5 µM) and boscalid (0.5 µM) did not induce changes in mitochondrial function when used separately, in contrast, when both fungicides were used in combination at the same concentration, we observed a significant alteration of the mitochondrial function of hepatocytes: there was a decrease in oxygen consumption rate, in the ATP level. In addition, the level of mitochondrial superoxide radical anion was increased leading to a decrease in the ratio reduced/oxidized glutathione, and an increase in viability.

Synthesis and Antifungal Activity Evaluation of Novel L-Carvone-Based 1,3,4-Thiadiazole-amide Derivatives as a Potential Succinate Dehydrogenase Inhibitor.

In an effort to explore new-type high-efficiency antifungal agents, 25 novel L-carvone-based 1,3,4-thiadiazole-amide derivatives were designed, synthesized, and structurally characterized by IR, 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS) analyses. The antifungal activity of the target compounds was preliminarily assayed at a concentration of 50 μg/mL, and boscalid, a commercialized fungicide identified as a succinate dehydrogenase inhibitor (SDHI), was employed as the positive control. It was found that all of the target compounds showed moderate to potent antifungal activity against the tested fungi compared to boscalid. Surprisingly, compound 4b exhibited broad-spectrum and significant inhibition activity against the growth of eight phytopathogenic strains with inhibitory rates of 67-89%. Further, the results of the EC50 value test suggested that the EC50 values of compound 4b against Physalospora piricola and Colletotrichum orbiculare were 16.33 and 18.06 μg/mL, respectively, and both of them were better than those of boscalid (16.64 and >50). Therefore, compound 4b deserves further study as a lead compound for novel fungicides. In addition, the inhibitory activity of compound 4b against succinate dehydrogenase (SDH) was evaluated as well to prove that compound 4b (IC50 = 3.38 μM) displayed higher SDH-inhibition activity than boscalid (IC50 = 7.02 μM). The binding mode of compound 4b and SDH was simulated by molecular docking and found to be similar to that of boscalid. The structure-activity relationships (SARs) of the target compounds were analyzed by establishing a 3D-QSAR model. Besides, a 4b-loaded complex 4b/CSTA on a reported L-carvone-based nanochitosan carrier CSTA containing the 1,3,4-thiadiazole-amide group was constructed, and its sustained release performance was investigated in the EtOH-H2O system (1:9, v/v). The complex 4b/CSTA exhibited preferred sustained release performance, indicating its potential for developing environmentally friendly nanofungicides.

Development and Biological Evaluation of New Diphenyl Ether Formylhydrazide Compounds as Potent Inhibitors of Succinate Dehydrogenase.

Succinate dehydrogenase (SDH), also recognized as succinate ubiquinone oxidoreductase (SQR), is considered one of the most promising targets for fungicide development, garnering significant international interest. We have focused on the development of highly effective, broad-spectrum-targeted SDH inhibitors. Using an active scaffold combining strategy, we designed and synthesized a series of novel diphenyl ether formylhydrazine derivatives, and most compounds have demonstrated broad-spectrum antifungal activity. Notably, compound M8 exhibited antifungal activity of more than 93% against four tested pathogen types at a concentration of 10 μg/mL, with an EC50 value below 0.3 μg/mL for each pathogen, outperforming boscalid. Additionally, compound M8 exhibited a control efficacy of 83% against Sclerotinia sclerotiorum on rapeseed leaves at a concentration of 200 μg/mL and demonstrated an 87% efficacy in controlling Fusarium graminearum on wheat ears when applied at 400 μg/mL. Structure-activity relationship research suggested that para-substituted benzene rings are more effective, offering stronger and more extensive antifungal potency. Further investigation, including enzyme inhibition assays, mycelial morphology observations, and molecular docking studies, suggests that the antifungal potency of M8 is due to the inhibition of its SDH activity. Therefore, our research positions compound M8 as a highly promising lead compound with broad-spectrum antifungal properties, potentially introducing a new class of fungicide.

Metabolic Regulation of Inflammation: Exploring the Potential Benefits of Itaconate in Autoimmune Disorders.

Itaconic acid and its metabolites have demonstrated significant therapeutic potential in various immune diseases. Originating from the tricarboxylic acid cycle in immune cells, itaconic acid can modulate immune responses, diminish inflammation, and combat oxidative stress. Recent research has uncovered multiple mechanisms through which itaconic acid exerts its effects, including the inhibition of inflammatory cytokine production, activation of anti-inflammatory pathways, and modulation of immune cell function by regulating cellular metabolism. Cellular actions are influenced by the modulation of metabolic pathways, such as inhibiting succinate dehydrogenase (SDH) activity or glycolysis, activation of nuclear-factor-E2-related factor 2 (Nrf2), boosting cellular defences against oxidative stress, and suppression of immune cell inflammation through the NF-κB pathway. This comprehensive review discusses the initiation, progression, and mechanisms of action of itaconic acid and its metabolites, highlighting their modulatory effects on various immune cell types. Additionally, it examines their involvement in immune disease like rheumatoid arthritis, multiple sclerosis, type 1 diabetes mellitus, and autoimmune hepatitis, offering greater understanding for creating new therapies for these ailments.

Antifungal activity of chalcone derivatives containing 1,2,3,4-tetrahydroquinoline and studies on them as potential SDH inhibitors.

A large number of pathogenic fungi have caused serious damage to the global crop yield, and drug resistance is always a topic that cannot be avoided for traditional fungicides. Therefore, finding efficient, green, and low-toxic fungicides is our primary task, which brings opportunities for the development of natural product green pesticides. Twenty chalcone derivatives containing 1,2,3,4-tetrahydroquinoline were designed and synthesized, and the compounds were tested for their fungicidal effects against eight plant pathogenic fungi in vitro. The results demonstrate that the original splicing did not have fungicidal activity, so a piperazine fragment was introduced; the test results revealed that H1-H10 all had good antifungal activity. Among them, H4 showed the highest inhibitory activity against Phytophthora capsici (Pc) with a median effect concentration (EC50) value of 5.2 μg/mL, which was higher than that of the control drugs Azoxystrobin (EC50 = 80.2 μg/mL) and Fluopyram (EC50 = 146.8 μg/mL). After the study, it was demonstrated that H4 mainly acted on the cell membrane against Phytophthora capsici and inhibited the activity of the marker enzyme of mitochondria (SDH) in the fungus. H4 has significant resistance to Phytophthora capsici and also plays a significant role in inhibiting SDH activity, providing a new direction for the development of green pesticides. © 2024 Society of Chemical Industry.

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Cyclobutrifluram.

Cyclobutrifluram, a succinate dehydrogenase inhibitor fungicide, is being evaluated as a seed-applied nematicide in cotton and soybean to manage plant-parasitic nematodes. Currently, there is no information on the toxicity, ovicidal activity, nematode recovery, or effects on nematode infection for Meloidogyne incognita or Rotylenchulus reniformis after exposure to low concentrations of cyclobutrifluram. Nematode toxicity assays were performed in aqueous solutions of cyclobutrifluram, and root infection assays were conducted on tomato. Nematode paralysis was observed after 2 h of exposure to 0.5 μg/ml cyclobutrifluram for both nematode species. Based on an assay of nematode motility, the 2-h effective concentration of fungicide required for 50% growth inhibition (EC50) value for M. incognita and R. reniformis was 0.48 and 1.07 μg/ml, respectively. In a comparable assay with a similar nematicide, continuous exposure to 0.5 μg/ml cyclobutrifluram for 24 h resulted in at least 45% more immotile nematodes for both species compared with those treated with 0.5 μg/ml fluopyram. Continuous exposure to concentrations greater than 1.0 μg/ml suppressed hatching for both species compared with the water control. Nematode recovery from paralysis was greater than 80% for M. incognita and R. reniformis 24 h after nematodes were rinsed and removed from a 1-h treatment to their respective 2-h EC50 concentrations. Nematode infection of tomato roots was reduced following a 1-h treatment with aqueous solutions of cyclobutrifluram, ranging from 0.12 to 0.48 μg/ml for M. incognita and 0.27 to 1.07 μg/ml for R. reniformis. Overall, the toxicity of cyclobutrifluram to these nematode species was greater than that of fluopyram, and although the effects of cyclobutrifluram were reversible, low concentrations were effective at reducing the ability of both nematodes to infect tomato roots.

Sensitivity of soybean (Glycine max L.) pathogens Diaporthe aspalathi, D. caulivora, and D. longicolla to Difenoconazole and Fluopyram fungicides

Diseases of soybean (Glycine max L.) caused by species of Diaporthe have resulted in estimated yield losses totaling $248.2 million in the U.S. over the past 10 years. To effectively manage species of Diaporthe, it is important to use an integrated approach. In this study, we evaluated the in vitro sensitivity of isolates of the soybean pathogens Diaporthe aspalathi, D. caulivora, and D. longicolla from 18 U.S. states to difenoconazole (a demethylation inhibitor fungicide) and fluopyram (a succinate dehydrogenase inhibitor fungicide). The fungicides were incorporated into 2% water agar (WA) in petri dishes at various concentrations. A mycelial plug of each isolate (n=59 for difenoconazole and n=55 for fluopyram) obtained from a 7-day-old culture was placed at the center of the WA and incubated in the dark. After five days for D. caulivora and D. longicolla, and eight days for D. aspalathi, the colony diameter was measured, and the corresponding percent inhibition and effective concentration at which 50% mycelial growth was inhibited (EC50) were determined. Significant differences in EC50 values (P<0.0001) were observed among the isolates of D. aspalathi (0.227 µg/ml), D. caulivora (0.130 µg/ml), and D. longicolla (1.860 µg/ml) for difenoconazole. Similarly, for fluopyram, the EC50 values varied significantly (P<0.001) among the D. aspalathi (2.233 µg/ml), D. caulivora (1.610 µg/ml), and D. longicolla (0.347 µg/ml) isolates. This study established sensitivity profiles for difenoconazole and fluopyram fungicides for D. aspalathi, D. caulivora, and D. longicolla, and provides valuable information that may help in the development of Diaporthe disease management program.

Resistance to the SDHI Fungicide Pydiflumetofen in Fusarium solani: Risk Assessment and Resistance-Related Point Mutation in FsSdhC Gene.

Peanut root rot (PRR) is a prevalent and destructive plant disease attributed to Fusarium solani. Pydiflumetofen (Pyd) is a succinate dehydrogenase inhibitor (SDHI) with antifungal activity against F. solani, yet its resistance mechanism has been inadequately explored. In this study, the EC50 values for Pyd against 93 F. solani strains ranged from 0.0095 to 0.3815 μg/mL, with all strains displaying a minimal inhibitory concentration (MIC) of ≤1 μg/mL. Four Pyd-resistant (PR) mutants were obtained, exhibiting stable resistance levels and comparable fitness to their parental strains in terms of mycelia growth, hyphal tip morphology, asexual reproduction, and virulence assessment. Five-point mutations, including FsSdhC1A82V, FsSdhC2L76M, FsSdhC2L135V, FsSdhC2F137L, and FsSdhC2F147L, were identified in the PR mutants. However, molecular docking analysis indicated that only FsSdhC1A82V and FsSdhC2L135V could influence the sensitivity of F. solani to Pyd. These findings help evaluate F. solani's resistance to Pyd and guide future PRR management with this fungicide.

Design, synthesis and antifungal activity of arylhydrazine analogs containing diphenyl ether fragments.

Succinate dehydrogenase (SDH) represents a critical target in the development of novel fungicides. To address the growing issue of resistance and safeguard the economic viability of agricultural production, the pursuit of new succinate dehydrogenase inhibitors (SDHIs) has emerged as a significant focus of contemporary research. In this project, 32 arylhydrazine derivatives containing diphenyl ether structural units were synthesized and evaluated for their fungicidal activities against Rhizoctonia solani, Sclerotinia sclerotiorum, Alternaria alternata, Gibberella zeae, Alternaria solani and Colletotrichum gloeosporioides. In an in vitro fungicidal activity assay, compound D6 showed significant inhibitory activity against R. solani with a half-maximum effective concentration (EC50) of 0.09 mg L-1. The in vivo fungicidal activity demonstrated that compound D6 inhibited R. solani by 95.39% in rice leaves, which was significantly better than that of boscalid (85.76%). The results of SDH enzyme assay, molecular docking simulation, mitochondrial membrane potential assay, cytoplasmic release studies and morphological observations demonstrated that the target compound D6 not only had significant SDH inhibitory activity, but also affected the membrane integrity of mycelium. Bioactivity screening and validation of the mechanism of action indicated that compound D6 was a potentially unique SDHI, acting on SDH while also affecting cell membrane permeability, which deserved further study. © 2024 Society of Chemical Industry.