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This review covers the situation with resistance to various systemic fungicides being developed in Venturia inaequalis worldwide and in Russia assessing the prospects for their further use. Information is provided about all fungicides used in Russia against apple scab and their efficacy at this point in time and each chemical class is described. Data are presented on the mechanisms of resistance to chemicals in the pathogen including at the molecular level. The problem of resistance of V. inaequalis and ways of solving it at the present level of scientific knowledge are discussed. [ABSTRACT FROM AUTHOR]

Late leaf spot, caused by Nothopassalora personata, is an economically important disease of peanut that routinely requires several applications of preventative fungicides. The objectives of this study were to quantify the risk of phenotypic fungicide resistance and potential cross-resistance among N. personata populations. A total of 59 samples of N. personata isolates were collected from 28 grower or research fields in South Carolina, Georgia, and Virginia. Phenotypic resistance of isolates was evaluated against 14 fungicides and a nontreated control, with active ingredients from the quinone outside inhibitor, demethylation inhibitor, and succinate-dehydrogenase inhibitor (SDHI) classes. Overall, visual incidence of lesion development 15% or greater was observed with nearly all isolates for at least one of the active ingredients tested. Correlations between active ingredients penthiopyrad and pydiflumetofen, as well as bixafen plus flutriafol and pydiflumetofen, and their lesion development risk indicate potential N. personata populations with SDHI cross-resistance. Although these data do not confirm the presence of genetic resistance markers, results paired with observed reduced efficacy in the field reinforce the strong need for an integrated approach in managing late leaf spot. In areas with high probabilities for resistance to several modes of action, longer rotations out of peanut, varieties with greater levels of resistance, earlier planting, and continued incorporation of active ingredients with a multi-site mode of action in fungicide programs are advised for preserving fungicide efficacy or reducing selection pressure. [Figure: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

We detected isolates with SdhC-I87F-conferring mutations that were slightly SDHI-adapted in the barley leaf rust Puccinia hordei in France and the UK in 2019. SdhC-I87F of P. hordei is orthologous to SdhC-I86F in Phakopsora pachyrhizi, and SdhC-I88F in Puccinia horiana induced SDHI resistance. Nevertheless, the field performance of SDHIs against P. hordei was good, although strains with SdhC-I87F dominated the field. The sensitivity ranges were narrow for wheat leaf rust and Puccinia triticina in 2019; however, isolates with slightly higher EC50 values were obtained in southern France and the eastern UK in 2021. These isolates of P. triticina harbored an orthologous SdhC-I87F-conferring mutation. The range of EC50 values for the SDHI fungicide inpyrfluxam overlapped between the wild type and SdhC-I87F isolates. Further analyses are currently underway. [ABSTRACT FROM AUTHOR]

The developing resistance of Venturia inaequalis to toxicants commonly used in systemic fungicides against apple scab has reduced their effectiveness, causing substantial fruit loss in orchards. To improve the situation and manage the resistance, a thorough analysis of the fitness potential among different pathogen biotypes, particularly those resistant to fungicides, is needed. In this study, the mycelial growth of V. inaequalis isolates with baseline sensitivity and resistance to one or more fungicides was assessed in vitro at four temperatures (6, 18, 27, and 30°C) and three agar concentrations in the nutrient medium (2, 4, and 6% m/V). Except for the mycelial growth at 27°C, the indicators of fitness predicted in vitro did not differ significantly between the V. inaequalis isolates with multiple resistance to fungicides and the biotypes with baseline sensitivity.

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.

Net blotch disease, caused by Pyrenophora teres f. teres (Ptt), is one of the most serious diseases of barley in Argentina. The in vitro sensitivity profile of Ptt to different fungicide mixtures currently used in Argentina was determined in isolates from different localities. Mycelial growth inhibition was measured, and the 50% inhibitory concentration (EC50) was estimated by simple logarithmic regression. In addition, the in vivo sensitivity of Ptt to the application of fluxapyroxad 5% + epoxiconazole 5% + pyraclostrobin 8.1% (FEP) was evaluated in greenhouse and field trials. The EC50 values ranged from 0.004 to 0.527 µg/mL, indicating that the fungicide mixtures tested were highly fungitoxic to all Ptt isolates tested. The in vivo and field fungicide efficacy averaged 99.9% and 79.5%, confirming a correlation between in vitro and in vivo sensitivity. The fungicide mixtures evaluated here were all highly fungitoxic and efficient for managing net blotch. [ABSTRACT FROM AUTHOR]

Growers often use alternations or mixtures of fungicides to slow down the development of resistance to fungicides. However, within a landscape, some growers will implement such resistance management methods, whereas others do not, and may even apply solo components of the resistance management program. We investigated whether growers using solo components of resistant management programs affect the durability of disease control in fields of those who implement fungicide resistance management. We developed a spatially implicit semidiscrete epidemiological model for the development of fungicide resistance. The model simulates the development of epidemics of spot-form net blotch disease, caused by the pathogen Pyrenophora teres f. maculata. The landscape comprises three types of fields, grouped according to their treatment program, with spore dispersal between fields early in the cropping season. In one field type, a fungicide resistance management method is implemented, whereas in the two others, it is not, with one of these field types using a component of the fungicide resistance management program. The output of the model suggests that the use of component fungicides does affect the durability of disease control for growers using resistance management programs. The magnitude of the effect depends on the characteristics of the pathosystem, the degree of inoculum mixing between fields, and the resistance management program being used. Additionally, although increasing the amount of the solo component in the landscape generally decreases the lifespan within which the resistance management program provides effective control, situations exist where the lifespan may be minimized at intermediate levels of the solo component fungicide. [ABSTRACT FROM AUTHOR]

In the context of global warming, the increasing frequency of compound dry–hot extremes pose varying degrees of threats to the natural environment and human society. However, due to the lack of long‐term and high‐accuracy meteorological observations, the characteristics and drivers of compound dry–hot extremes over a century‐long period is still poorly investigated in China. Here we characterize the spatiotemporal variations of growing‐season (May–September) compound dry–hot events (CDHEs) over China using Standardized Dry and Hot Index (SDHI) calculated by monthly temperature and precipitation during 1901–2017. The influences of precipitation and temperature extremes, as well as large‐scale climate indices (i.e., El Niño–Southern Oscillation Index [ENSO], Atlantic Multidecadal Oscillation [AMO], North Atlantic Oscillation [NAO], Pacific Decadal Oscillation [PDO] and North Pacific [NP]) on CDHEs were then explored using the relative contribution analysis, Pearson correlation analysis and cross‐wavelet spectrum analysis. Our findings reveal a significant increase in the occurrence of different severity levels of CDHEs in China with their spatial extent gradually increase, practically since the end of the 20th century. Due to the exacerbation of drought conditions in China since the mid‐20th century, the regions where the Standardized Precipitation Index (SPI) has a more prominent contribution to the SDHI have gradually expanded, predominantly in the eastern, northern and northwestern parts of China. The significant influence of large‐scale climate indices, particularly ENSO and AMO, on the occurrence of compound dry–hot extremes in China is noteworthy, as these indices control the variability of precipitation and temperature, respectively. The study findings demonstrate that AMO exhibits a more significant correlation with SDHI in all subregions of China, while ENSO exhibits marginally stronger periodic coherence with SDHI than the other indices. This study offers valuable insights and references for unravelling long‐term development process of and the underlying influence mechanisms of significant climate patterns on the growing‐season CDHEs in China. [ABSTRACT FROM AUTHOR]

Compound dry hot events (CDHEs), where hot events and droughts coexist, have received a lot of attention lately due to their catastrophic effects on the economy, environment and human health. In this study, we use two CDHE indices, the Standardized Compound Event Indicator (SCEI) and the Standardized Dry and Hot Index (SDHI), to assess changes in CDHE characteristics (severity, frequency, spatial extent) over the historical past and future CMIP6 simulations across the Indian subcontinent. To understand the role of the drought index selected on CDHE characterization two drought indices namely the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) are employed in the calculation of the CDHE indices. Further, the role of climatic oscillations such as El Nino Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Equatorial Indian Ocean Monsoon Oscillation and Indian Ocean Dipole in modulating CDHE characteristics have also been explored. Results show that SPI and SPEI based CDHE indices exhibit contrasting trends in northern India, while similar trends are observed in southern India in the historical past. Also, more frequent, extended, and severe CDHEs are reported by CDHE indices calculated using SPEI than by SPI. Temperature is found to be the dominant factor contributing to increases in CDHEs in the recent past and ENSO phases significantly modulate the severity and frequency of CDHE events in India. CMIP6 simulations generally report an increase in CDHE events for a 3°C global warming scenario. Overall, our findings show that the choice of the drought index has a greater impact on CDHE characterization than the choice of the CDHE index itself. Results from this study provide useful information towards understanding the risk of CDHEs in India under global warming and urge for the development and implementation of adaptation and mitigation measures. [ABSTRACT FROM AUTHOR]

Fungicides are widely used in agriculture for crop protection. Succinate dehydrogenase inhibitors (SDHIs) and strobilurins inhibit mitochondria electron transport chain (ETC) in fungi, by blocking complex II and complex III, respectively. Questions regarding their selectivity of action for fungi have been raised in the literature, and we previously showed that boscalid and bixafen (SDHIs) alter the mitochondrial function of human hepatocytes. Here, we analyzed the impact of the exposure of human hepatocytes to pyraclostrobin, a fungicide belonging to the class of strobilurins. Using electron paramagnetic resonance (EPR), we observed a decrease in oxygen consumption rate (OCR) and an increase in mitochondrial superoxide levels after 24 h exposure to 0.5 µM concentration. As a consequence, the content in ATP amount in the cells was reduced, the ratio reduced/oxidized glutathione was decreased, and a decrease in cell viability was observed using three different assays (PrestoBlue, crystal violet, and annexin V assays). In addition, as SDHIs and strobilurins are commonly associated in commercial preparations, we evaluated a potential "cocktail" toxic effect. We selected low concentrations of boscalid (0.5 µM) and pyraclostrobin (0.25 µM) that did not induce a mitochondrial dysfunction in liver cells when used separately. In sharp contrast, when both compounds were used in combination at the same concentration, we observed a decrease in OCR, an increase in mitochondrial superoxide production, a decrease in the ratio reduced/oxidized glutathione, and a decrease in cell viability in three different assays. [ABSTRACT FROM AUTHOR]

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Phoma stem canker, caused by Leptosphaeria spp. is generally managed with demethylation inhibitor (DMI) fungicides in the Czech Republic. However, there have been reports of resistance to DMIs in L. maculans populations. Fungicide resistance management recommends the application of fungicides with different modes of action, either as mixtures or in rotation with other fungicide classes. The objective, therefore, was to evaluate the efficacy of boscalid, dimoxystrobin and a mixture of boscalid and dimoxystrobin, belonging to the succinate dehydrogenase inhibitor and quinone outside inhibitor fungicide groups, respectively, on L. maculans isolates. A total of 41 and 285 isolates were tested using the mycelial growth and microtitre plate assays, respectively. The EC50 values for the mycelial growth plate method ranged from 0.026-0.984 µg/mL and 0.097-1.653 µg/mL for boscalid and boscalid + dimoxystrobin, respectively. For dimoxystrobin, the EC50 range was wide, between 0.053-95.59 µg/mL. The EC50 values for the microtitre plate assay ranged from 0.001 496-0.836 3 µg/mL and 7.3 × 10-4-2.801 µg/mL for boscalid and dimoxystrobin, respectively. The results also showed that the L. maculans conidia were more sensitive to boscalid and dimoxystrobin than mycelia.

This study aimed at the development and validation of an accurate, more affordable, and precise digital imaging resazurin-based fungicide sensitivity colorimetric assay (COL-assay) for fungal plant pathogens from the genera Mycosphaerella and Pyricularia. This proposed digital imaging assay was based on colorimetric estimates of resazurin reduction, which was used as a metabolic indicator of fungal respiration activity on microplate cultures. As fungal model systems, we used the yellow and black Sigatoka pathogens [Mycosphaerella musicola (Mm) and M. fijiensis (Mf), respectively] and the wheat blast pathogen, Pyricularia oryzae Triticum lineage (PoTl), which were previously characterized for QoI, DMI, and SDHI fungicide sensitivity. We then compared the classical spectrophotometry detection assay (SPEC-assay) with the proposed COL-assay based on the analyses of digital images of the microplates' cultures captured with mobile phone cameras on a handmade trans-illuminator built for poorly equipped labs. Qualitatively, in terms of accuracy, there was full correspondence between the SPEC-assay and the COL-assay according to the fungal EC50 or the relative growth classes on QoI, SDHI, and DMI fungicides for both Mycosphaerella and Pyricularia pathogens. We also observed a strong to very strong correlation coefficient between the COL-assay and the SPEC-assay fungicide sensitivity values for the QoI azoxystrobin, the SDHI fluxapyroxad, and the DMI tebuconazole. Our conclusion was that the COL-assay had a similar accuracy as the SPEC-assay (i.e., resulted in similar fungicide-sensitivity categories for both resistant or sensitive fungal isolates) and high precision. By openly sharing here the COL-assay's full methodology, and the blueprints of the handmade trans-illuminator, we foresee its adoption by poorly equipped labs throughout the country as an affordable venue for monitoring the fungicide resistance status of populations of important fungal plant pathogens such as M. fijiensis, M. musicola, and P. oryzae Triticum and Oryza lineages. [ABSTRACT FROM AUTHOR]

Zymoseptoria tritici causes the disease known as septoria leaf blotch in winter wheat and is a major factor in yield loss worldwide. Farmers are inclined to use fungicides to protect their crops; however, the efficacy of these measures is rapidly decreasing due to the natural mechanisms of mutation emergence in pathogen populations. Increasing fungicide resistance is being recorded worldwide, therefore, screening of the current situation in Lithuania is essential to determine the subsequent steps of crop protection strategies. In this study, in vitro fungicide sensitivity tests, mutation detection, and field experiments were carried out. The mean EC50 values for prothioconazoledesthio and mefentrifluconazole were 0.14 and 0.28 mg/l, respectively. Increased frequency of the mutation S524T, linked to DMIs resistance, was observed. Results revealed that the dominant point mutation in the gene CYP51 was I381V, and the most frequent CYP51 haplotype was D13 (V136C, I381V, Y461H, S524T). The mutation G143A, linked to QoI resistance, was detected in 3/4 of the population. Mutations conferring resistance to SDHIs were not detected in single pycnidium isolates. Two-year field experiments likewise showed no decline in field efficacy of SDHI fungicide in Lithuania. Moreover, the baseline sensitivity of the Lithuanian Z. tritici population to QiI fungicide fenpicoxamid was established. The findings of this study provide an update on the current status of fungicide resistance in the Lithuanian Z. tritici population. [ABSTRACT FROM AUTHOR]

Ramularia leaf spot (RLS), caused by the fungus Ramularia collo-cygni, has recently become widespread in Europe. Succinate dehydrogenase inhibitor (SDHI) and demethylation inhibitor (DMI) fungicides are mainly applied for disease control on barley fields, but pathogen isolates with a reduced sensitivity can cause difficulties. There is an urgent need for new spring barley cultivars that are more resistant to RLS development and can inhibit R. collo-cygni epidemics.

Zymoseptoria tritici causes the disease known as septoria leaf blotch in winter wheat and is a major factor in yield loss worldwide. Farmers are inclined to use fungicides to protect their crops; however, the efficacy of these measures is rapidly decreasing due to the natural mechanisms of mutation emergence in pathogen populations. Increasing fungicide resistance is being recorded worldwide, therefore, screening of the current situation in Lithuania is essential to determine the subsequent steps of crop protection strategies. In this study, in vitro fungicide sensitivity tests, mutation detection, and field experiments were carried out. The mean EC50 values for prothioconazole-desthio and mefentrifluconazole were 0.14 and 0.28 mg/l, respectively. Increased frequency of the mutation S524T, linked to DMIs resistance, was observed. Results revealed that the dominant point mutation in the gene CYP51 was I381V, and the most frequent CYP51 haplotype was D13 (V136C, I381V, Y461H, S524T). The mutation G143A, linked to QoI resistance, was detected in ¾ of the population. Mutations conferring resistance to SDHIs were not detected in single pycnidium isolates. Two-year field experiments likewise showed no decline in field efficacy of SDHI fungicide in Lithuania. Moreover, the baseline sensitivity of the Lithuanian Z. tritici population to QiI fungicide fenpicoxamid was established. The findings of this study provide an update on the current status of fungicide resistance in the Lithuanian Z. tritici population.

Phoma stem canker, caused by Leptosphaeria spp. is generally managed with demethylation inhibitor (DMI) fungicides in the Czech Republic. However, there have been reports of resistance to DMIs in L. maculans populations. Fungicide resistance management recommends the application of fungicides with different modes of action, either as mixtures or in rotation with other fungicide classes. The objective, therefore, was to evaluate the efficacy of boscalid, dimoxystrobin and a mixture of boscalid and dimoxystrobin, belonging to the succinate dehydrogenase inhibitor and quinone outside inhibitor fungicide groups, respectively, on L. maculans isolates. A total of 41 and 285 isolates were tested using the mycelial growth and microtitre plate assays, respectively. The EC50 values for the mycelial growth plate method ranged from 0.026–0.984 µg/mL and 0.097–1.653 µg/mL for boscalid and boscalid + dimoxystrobin, respectively. For dimoxystrobin, the EC50 range was wide, between 0.053–95.59 µg/mL. The EC50 values for the microtitre plate assay ranged from 0.001 496–0.836 3 µg/mL and 7.3 × 10–4–2.801 µg/mL for boscalid and dimoxystrobin, respectively. The results also showed that the L. maculans conidia were more sensitive to boscalid and dimoxystrobin than mycelia. [ABSTRACT FROM AUTHOR]

BACKGROUND: Rice (Oryza sativa) is an important cereal crop around the world, and has constantly been threaten by the most destructive fungus Magnaporthe oryzae. Pydiflumetofen, a novel succinate dehydrogenase inhibitor (SDHI), is currently being used for controlling various fungal diseases. However, the potential resistance risk of M. oryzae to pydiflumetofen has remained unclear to date, and finding the resistance mechanism is critical for the usage of this fungicide. RESULTS: The M. oryzae strain Guy11 is sensitive to pydiflumetofen, with EC50 value of 1.24 μg mL−1. 58 pydiflumetofen‐resistant (PR) mutants were obtained through pydiflumetofen‐induced spontaneous mutation, with a mean EC50 value >500 μg mL −1, and the resistance factor (RF) >400. The PR mutants displayed positive cross‐resistance to carboxin, but were more sensitive to fluopyram. Sequencing analysis showed that all PR mutants presented a cytosine‐to‐thymine transition at nucleotide position +1218, resulting in a replacement of histidine 245 by tyrosine (H245Y) on MoSdhB. The mutation of MoSdhB exhibited strong resistant phenotype, but no detectable growth deficits in fungal development, including vegetative growth and pathogenicity of M. oryzae. An allele‐specific PCR for rapid detection of the H245Y mutants was established in M. oryzae. CONCLUSION: The M. oryzae is sensitive to pydiflumetofen, and shows a medium to high resistance risk to pydiflumetofen. A point mutation of MoSdhB (H245Y) is responsible for the fungal resistance to pydiflumetofen in M. oryzae. © 2022 Society of Chemical Industry. The M. oryzae is sensitive to pydiflumetofen and shows a medium to high resistance risk to pydiflumetofen. A single histidine mutation of MoSdhB (H245Y) is responsible for the fungal resistance to pydiflumetofen in M. oryzae. [ABSTRACT FROM AUTHOR]

Widespread resistance to QoIs, DMI and SDHIs fungicides has been reported for Brazilian populations of the wheat blast pathogen Pyricularia oryzae Triticum lineage (PoTl). A pre-existing resistance mechanism not associated with target site mutations has been indicated for resistance to DMIs and SDHIs, with strong indication that PoTl has multidrugresistance (MDR). Therefore, the main objective of this study was to test the hypothesis that resistance to DMI and SDHI fungicides detected in PoTl was due to efflux pump mediated MDR mechanism(s) by characterizing the sensitivity to antifungal efflux pump substrates. Four antifungal substrates were tested: tolnaftate (TOL), cycloheximide (CHX), rhodamine 6G (RH6G) and triphenyltin chloride (TPCL). TPCL and RH6G were considered the most relevant indicators for enhanced MDR activity. Among the 16 PoTl isolates tested, 9 were insensitive to TPCL, 1 to TOL, 16 to RH6G and 1 to CHX. The PoTl isolates were grouped into four distinct multidrug resistance phenotypes (MDRPs) based on resistance to combinations of fungicides and antifungal efflux pump substrates. Insensitivity to TPCL, RH6G and or TOL correlated well with DMI insensitivity, but MDR was not associated with SDHI resistance. The identification of multiple MDRP phenotypes associated with DMI resistance in our study warrants further research aimed at revealing the exact mechanisms of multidrug resistance in the wheat blast pathogen, including efflux pumps overexpression via transcriptomic analyses of differentially expressed genes; identification and discovery of mutations associated with changes in promoter regions or transcription factors of efflux transporters associated with multidrug resistance. [ABSTRACT FROM AUTHOR]

Improvements in agricultural production are needed, as the growing human population demands more resources and exerts stronger effects on climate. Water scarcity is one of the main factors limiting the yield of maize in many regions of the world. One possible method to mitigate the negative effects of drought is seed mortars; its use improves plant development from the early stages onwards. In this study, we tested 12 various seed treatments with and without succinate dehydrogenase inhibitors (SDHI; sedaxane) on maize "SY Fanatic." Physiological parameters of germinating seeds, of young maize seedlings under drought, and of seedlings recuperated from drought were assessed and compared across 12 seed treatments and with non-stressed plants. The seed treatments varied greatly in their influence on the germination and the physiological state of seedlings under drought and after regeneration. Seeds under treatments No. 6, 11, and 12 showed the highest germination energy (97.3%). The use of SDHI-containing seed treatments significantly improved the development of the maize root system. The longest roots, ~13 cm in length, were recorded for treatments No. 6 and 12, both containing sedaxane. These treatments also boosted the functioning of plants growing under optimal soil moisture conditions and under drought stress, influencing the photosynthesis process, increasing the absorption of CO2, and improving the parameters of chlorophyll fluorescence in relation to non-treated controls. Our data indicated that using substances from the SDHI group can possibly reduce the drought-related stress reactions in maize, helping this important crop to face the progressing climate change. [ABSTRACT FROM AUTHOR]

Research focused on succinate dehydrogenase (SDH) and its substrate, succinate, culminated in the 1950s accompanying the rapid development of research dedicated to bioenergetics and intermediary metabolism. This allowed researchers to uncover the implication of SDH in both the mitochondrial respiratory chain and the Krebs cycle. Nowadays, this theme is experiencing a real revival following the discovery of the role of SDH and succinate in a subset of tumors and cancers in humans. The aim of this review is to enlighten the many questions yet unanswered, ranging from fundamental to clinically oriented aspects, up to the danger of the current use of SDH as a target for a subclass of pesticides. [ABSTRACT FROM AUTHOR]

Improvements in agricultural production are needed, as the growing human population demands more resources and exerts stronger effects on climate. Water scarcity is one of the main factors limiting the yield of maize in many regions of the world. One possible method to mitigate the negative effects of drought is seed mortars; its use improves plant development from the early stages onwards. In this study, we tested 12 various seed treatments with and without succinate dehydrogenase inhibitors (SDHI; sedaxane) on maize “SY Fanatic.” Physiological parameters of germinating seeds, of young maize seedlings under drought, and of seedlings recuperated from drought were assessed and compared across 12 seed treatments and with non-stressed plants. The seed treatments varied greatly in their influence on the germination and the physiological state of seedlings under drought and after regeneration. Seeds under treatments No. 6, 11, and 12 showed the highest germination energy (97.3%). The use of SDHI-containing seed treatments significantly improved the development of the maize root system. The longest roots, ~13 cm in length, were recorded for treatments No. 6 and 12, both containing sedaxane. These treatments also boosted the functioning of plants growing under optimal soil moisture conditions and under drought stress, influencing the photosynthesis process, increasing the absorption of CO2, and improving the parameters of chlorophyll fluorescence in relation to non-treated controls. Our data indicated that using substances from the SDHI group can possibly reduce the drought-related stress reactions in maize, helping this important crop to face the progressing climate change.

Mitochondrial electron transfer inhibitors at complex II (METI-II), also referred to as succinate dehydrogenase inhibitors (SDHI), represent a recently developed class of acaricides encompassing cyflumetofen, cyenopyrafen, pyflubumide and cyetpyrafen. Despite their novelty, resistance has already developed in the target pest, Tetranychus urticae. In this study a new mutation, H146Q in a highly conserved region of subunit B of complex II, was identified in a T. urticae population resistant to all METI-IIs. In contrast to previously described mutations, H146Q is located outside the ubiquinone binding site of complex II. Marker-assisted backcrossing of this mutation in a susceptible genetic background validated its association with resistance to cyflumetofen and pyflubumide, but not cyenopyrafen or cyetpyrafen. Biochemical assays and the construction of inhibition curves with isolated mitochondria corroborated this selectivity. In addition, phenotypic effects of H146Q, together with the previously described H258L, were further examined via CRISPR/Cas9 gene editing. Although both mutations were successfully introduced into a susceptible T. urticae population, the H146Q gene editing event was only recovered in individuals already harboring the I260V mutation, known to confer resistance towards cyflumetofen. The combination of H146Q + I260V conferred high resistance levels to all METI-II acaricides with LC 50 values over 5000 mg a.i./L for cyflumetofen and pyflubumide. Similarly, the introduction of H258L via gene editing resulted in high resistance levels to all tested acaricides, with extreme LC 50 values (>5000 mg a.i./L) for cyenopyrafen and cyetpyrafen, but lower resistance levels for pyflubumide and cyflumetofen. Together, these findings indicate that different mutations result in a different cross-resistance spectrum, probably also reflecting subtle differences in the binding mode of complex II acaricides. [Display omitted] • Succinate dehydrogenase inhibitors (SDHI) are recently developped acaricides. • A population resistant to all commercial SDHI acaricides was detected. • A H146Q mutation in sdhB was validated by marker-assisted backcrossing, biochemical assays and CRISPR-Cas9 knock-in. • H146Q confers high levels of resistance to cyflumetofen and pyflubumide, but not cyenopyrafen and cyetpyrafen. [ABSTRACT FROM AUTHOR]

Definition: Ramularia leaf spot (RLS), caused by the fungus Ramularia collo-cygni, has recently become widespread in Europe. Succinate dehydrogenase inhibitor (SDHI) and demethylation inhibitor (DMI) fungicides are mainly applied for disease control on barley fields, but pathogen isolates with a reduced sensitivity can cause difficulties. There is an urgent need for new spring barley cultivars that are more resistant to RLS development and can inhibit R. collo-cygni epidemics. [ABSTRACT FROM AUTHOR]

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.

This study aimed at the development and validation of an accurate, more affordable, and precise digital imaging resazurin-based fungicide sensitivity colorimetric assay (COL-assay) for fungal plant pathogens from the genera Mycosphaerella and Pyricularia. This proposed digital imaging assay was based on colorimetric estimates of resazurin reduction, which was used as a metabolic indicator of fungal respiration activity on microplate cultures. As fungal model systems, we used the yellow and black Sigatoka pathogens [Mycosphaerella musicola (Mm) and M. fijiensis (Mf), respectively] and the wheat blast pathogen, Pyricularia oryzae Triticum lineage (PoTl), which were previously characterized for QoI, DMI, and SDHI fungicide sensitivity. We then compared the classical spectrophotometry detection assay (SPEC-assay) with the proposed COL-assay based on the analyses of digital images of the microplates’ cultures captured with mobile phone cameras on a handmade trans-illuminator built for poorly equipped labs. Qualitatively, in terms of accuracy, there was full correspondence between the SPEC-assay and the COL-assay according to the fungal EC50 or the relative growth classes on QoI, SDHI, and DMI fungicides for both Mycosphaerella and Pyricularia pathogens. We also observed a strong to very strong correlation coefficient between the COL-assay and the SPEC-assay fungicide sensitivity values for the QoI azoxystrobin, the SDHI fluxapyroxad, and the DMI tebuconazole. Our conclusion was that the COL-assay had a similar accuracy as the SPEC-assay (i.e., resulted in similar fungicide-sensitivity categories for both resistant or sensitive fungal isolates) and high precision. By openly sharing here the COL-assay’s full methodology, and the blueprints of the handmade trans-illuminator, we foresee its adoption by poorly equipped labs throughout the country as an affordable venue for monitoring the fungicide resistance status of populations of important fungal plant pathogens such as M. fijiensis, M. musicola, and P. oryzae Triticum and Oryza lineages.

Bioisosteric silicon replacement has proven to be a valuable strategy in the design of bioactive molecules for crop protection and drug development. Twenty-one novel carboxamides possessing a silicon-containing biphenyl moiety were synthesized and tested for their antifungal activity and succinate dehydrogenase (SDH) enzymatic inhibitory activity. Among these novel succinate dehydrogenase inhibitors (SDHIs), compounds 3a , 3e , 4l, and 4o possessing appropriate c log P and topological polar surface area values showed excellent inhibitory effects against Rhizoctonia solani , Sclerotinia sclerotiorum , Botrytis cinerea , and Fusarium graminearum at 10 mg/L in vitro, and the EC 50 values of 4l and 4o were 0.52 and 0.16 mg/L against R. solani and 0.066 and 0.054 mg/L against S. sclerotiorum , respectively, which were superior to those of Boscalid. Moreover, compound 3a demonstrated superior SDH enzymatic inhibitory activity (IC 50 = 8.70 mg/L), exhibiting 2.54-fold the potency of Boscalid (IC 50 = 22.09 mg/L). Docking results and scanning electron microscope experiments revealed similar mode of action between compound 3a and Boscalid. The new silicon-containing carboxamide 3a is a promising SDHI candidate that deserves further investigation.

BACKGROUND: Fungicides of the succinate dehydrogenase inhibitors (SDHIs) group have been used in soybean to control Asian soybean rust (ASR) caused by Phakopsora pachyrhizi. Fungal populations with less sensitivity to SDHI fungicides have been reported since 2015. RESULTS: In this study, fungal sensitivity to benzovindiflupyr (BZV) and fluxapyroxad (FXD) was assessed using a total of 770 P. pachyrhizi populations sampled over four soybean growing seasons. Cross‐resistance, intrinsic activity, and frequency of SDHC‐I86F mutation were also analyzed. The average effective concentration to inhibit 50% (EC50) and SDHC‐I86F frequency increased over the 2015/2016, 2016/2017, 2017/2018 and 2018/2019 soybean‐seasons. Fourteen P. pachyrhizi populations had the EC50 value above 10 mg L−1 for both carboxamides. No difference was found in intrinsic active to BZV and FXD fungicides for sensitive P. pachyrhizi populations. For P. pachyrhizi classified as less sensitive BZV showed the highest fungitoxicity effect. High frequency of the C‐I86F mutation was observed in samples collected in volunteer soybean plants. The maximum frequency of SDHC‐I86F mutation in the population was 50% and resulting in ASR populations with low sensitivity to SDHIs. A low correlation between bioassay and SDHC‐I86F mutation was observed possible due to the dikaryotic nature of rust fungi or other mutations in the other succinate dehydrogenase subunits. CONCLUSION: The present work provides an overview of a large sampling size of P. pachyrhizi populations and their performance over the four crop seasons. The high frequency of SDHC‐I86F mutation and low sensitivity to SDHIs are widely distributed in the main soybean growing regions in Brazil and present in volunteer plants in the soybean‐free period. Further detailed studies are needed to identify novel point mutations affecting the effectiveness of SDHIs. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Fungicide resistance has become a challenging problem in management of Septoria tritici blotch (STB), caused by Zymoseptoria tritici, the most destructive disease of winter wheat throughout western and northern Europe. To ensure the continued effectiveness of those fungicides currently used, it is essential to monitor the development and spread of such resistance in field populations of the pathogen. Since resistance to the key families of fungicides used for STB control (demethyalation inhibitors or azoles, succinate dehydrogenase inhibitors or SDHIs and Quinone outside Inhibitors or QoIs) is conferred through target-site mutations, the potential exists to monitor resistance through the molecular detection of alterations in the target site genes. As more efficient fungicides were developed and applied, the pathogen has continuously adapted through accumulating multiple target-site alterations. In order to accurately monitor these changes in field populations, it is therefore becoming increasingly important to completely sequence the targeted genes. Here we report the development of a PacBio assay that facilitates the multiplex amplification and long-read sequencing of the target gene(s) for the azole (CYP51), SDHI (Sdh B, C, and D), and QoI (cytochrome b) fungicides. The assay was developed and optimised using three Irish Z. tritici collections established in spring 2017, which capture the range of fungicide resistance present in modern European populations of Z. tritici. The sequences obtained through the PacBio assay were validated using traditional Sanger sequencing and in vitro sensitivity screenings. To further exploit the long-read and high throughput potential of PacBio sequencing, an additional nine housekeeping genes (act, BTUB, cal, cyp, EF1, GAPDH, hsp80-1, PKC, TFC1) were sequenced and used to provide comprehensive Z. tritici strain genotyping.

BACKGROUND: Reliance on fungicides to manage disease creates selection pressure for the evolution of resistance in fungal and oomycete pathogens. Rust fungi (Pucciniales) are major pathogens of cereals and other crops and have been classified as low‐risk for developing resistance to fungicides; no case of field failure of fungicides in a cereal rust disease has yet been recorded. Recently, the Asian soybean rust pathogen, Phakopsora pachyrhizi evolved resistance to several fungicide classes, prompting us to screen a large sample of the globally widespread wheat yellow rust pathogen, Puccinia striiformis f. sp. tritici (Pst), for mutations associated with fungicide resistance. RESULTS: We evaluated 363 Pst isolates from Europe, the USA, Ethiopia, Chile, China and New Zealand for mutations in the target genes of demethylase inhibitor (DMI; Cyp51) and succinate dehydrogenase inhibitor (SDHI; SdhB, SdhC and SdhD) fungicides. A high proportion of Pst isolates carrying a Y134F DMI resistance‐associated substitution in the Cyp51 gene was found among those from China and New Zealand. A set of geographically diverse Pst isolates was also found to display a substitution in SdhC (I85V) that is homologous to that reported recently in P. pachyrhizi and linked to SDHI resistance. CONCLUSION: The identification of resistance‐associated alleles confirms that cereal rusts are not immune to fungicide resistance and that selection for resistance evolution is operating at high levels in certain locations. It highlights the need to adopt fungicide resistance management practices and to monitor cereal rust species for development of resistance. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Widespread resistance to QoIs, DMI and SDHIs fungicides has been reported for Brazilian populations of the wheat blast pathogen Pyricularia oryzae Triticum lineage (PoTl). A pre-existing resistance mechanism not associated with target site mutations has been indicated for resistance to DMIs and SDHIs, with strong indication that PoTl has multidrugresistance (MDR). Therefore, the main objective of this study was to test the hypothesis that resistance to DMI and SDHI fungicides detected in PoTl was due to efflux pump mediated MDR mechanism(s) by characterizing the sensitivity to antifungal efflux pump substrates. Four antifungal substrates were tested: tolnaftate (TOL), cycloheximide (CHX), rhodamine 6G (RH6G) and triphenyltin chloride (TPCL). TPCL and RH6G were considered the most relevant indicators for enhanced MDR activity. Among the 16 PoTl isolates tested, 9 were insensitive to TPCL, 1 to TOL, 16 to RH6G and 1 to CHX. The PoTl isolates were grouped into four distinct multidrug resistance phenotypes (MDRPs) based on resistance to combinations of fungicides and antifungal efflux pump substrates. Insensitivity to TPCL, RH6G and or TOL correlated well with DMI insensitivity, but MDR was not associated with SDHI resistance. The identification of multiple MDRP phenotypes associated with DMI resistance in our study warrants further research aimed at revealing the exact mechanisms of multidrug resistance in the wheat blast pathogen, including efflux pumps overexpression via transcriptomic analyses of differentially expressed genes; identification and discovery of mutations associated with changes in promoter regions or transcription factors of efflux transporters associated with multidrug resistance.

Cercospora species cause cercospora leaf blight (CLB) and purple seed stain (PSS) on soybean. Because there are few resistant soybean varieties available, CLB/PSS management relies heavily upon fungicide applications. Sensitivity of 62 Argentinian Cercospora isolates to demethylation inhibitor (DMI), methyl benzimidazole carbamate (MBC), quinone outside inhibitor (QoI), succinate dehydrogenase inhibitor (SDHI) fungicides, and mancozeb was determined in this study. All isolates were sensitive to difenoconazole, epoxiconazole, prothioconazole, tebuconazole, and cyproconazole (EC50 values ranged from 0.006 to 2.4 µg/ml). In contrast, 51% of the tested isolates were sensitive (EC50 values ranged from 0.003 to 0.2 µg/ml), and 49% were highly resistant (EC50 > 100 µg/ml) to carbendazim. Interestingly, all isolates were completely resistant to azoxystrobin, trifloxystrobin, and pyraclostrobin, and insensitive to boscalid, fluxapyroxad, and pydiflumetofen (EC50 > 100 µg/ml). The G143A mutation was detected in 82% (53) of the QoI‐resistant isolates and the E198A mutation in 97% (31) of the carbendazim‐resistant isolates. No apparent resistance mutations were detected in the succinate dehydrogenase genes (subunits sdhB, sdhC, and sdhD). Mancozeb completely inhibited mycelial growth of the isolates evaluated at a concentration of 100 µg/ml. All Argentinian Cercospora isolates were sensitive to the DMI fungicides tested, but we report for the first time resistance to QoI and MBC fungicides. Mechanism(s) other than fungicide target‐site modification may be responsible for resistance of Cercospora to QoI and MBC fungicides. Moreover, based on our results and on the recent introduction of SDHI fungicides on soybean in Argentina, Cercospora species causing CLB/PSS are insensitive (naturally resistant) to SDHI fungicides. Insensitivity must be confirmed under field conditions. [ABSTRACT FROM AUTHOR]

Demethylation inhibitor (DMI) and succinate dehydrogenase inhibitor (SDHI) fungicides are currently relied upon for the control of septoria tritici blotch (STB) in European wheat fields. However, multiple mutations have occurred over time in the genes encoding the targeted proteins that have led to a practical loss of fungicide efficacies. Among the different amino acid substitutions in Zymoseptoria tritici associated with resistance to these fungicides, S524T in CYP51 (DMI target) and H152R in SdhC (SDHI target) are regarded as conferring the highest resistance factors to DMI and SDHI, respectively. To facilitate further studies on the monitoring and selection of these substitutions in Z. tritici populations, a multiplex allele‐specific quantitative PCR (qPCR) assay allowing for estimation of both allele frequencies in bulk DNA matrices was developed. The assay was then used on complex DNA samples originating from a spore trap network set up in Belgium, Denmark, Sweden, and Ireland in 2017 and 2018, as well as on leaf samples with symptoms. The S524T allele was present in all field samples and its proportion was significantly higher in Ireland than in Belgium, whereas the proportion of H152R was only sporadically present in both countries. The frequency of S524T varied greatly in the airborne inoculum of all four countries; however, the H152R allele was never detected in the airborne inoculum. The method developed in this study can be readily adopted by other laboratories and used for multiple applications including resistance monitoring in field populations of Z. tritici. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) is caused by the ascomycete Zymoseptoria tritici and one of the predominating diseases in wheat (Triticum aestivum) in Europe. The control of STB is highly reliant on frequent fungicide applications. The primary objective of this study was to assess sensitivity levels of Z. tritici to different fungicide groups. The fungicides included in this study were epoxiconazole, prothioconazole-desthio, tebuconazole, and fluxapyroxad. A panel of 63 isolates from Estonia, Latvia, and Lithuania, and 10 isolates from Finland were tested. Fungicide sensitivity testing was carried out as a bioassay analyzing single pycnidium isolates on different fungicide concentrations. The average EC50 value in Baltic countries and Finland to epoxiconazole was high ranging from 1.04 to 2.19 ppm. For prothioconazole-desthio and tebuconazole, EC50 varied from 0.01 to 0.24 ppm, and 1.25 to 18.23 ppm, respectively. The average EC50 value for fluxapyroxad varied from 0.07 to 0.33 ppm. To explain the range of sensitivity, the samples were analyzed for CYP51 and Sdh mutations, as well as cytb G143A, CYP51 overexpression, and multidrug resistance (MDR). Frequencies of ZtCYP51 mutations D134G, V136A/C, A379G, I381V, and S524T in the Finnish-Baltic region were lower than in other European countries, but have increased compared to previous years. The frequency of cytb G143A conferring strobilurin resistance also augmented to 50–70% in the Z. tritici populations from Estonia, Finland, Latvia, and Lithuania. No Sdh mutations were found in this study, and neither strains of MDR phenotypes. However, we found a strain harboring a previously unknown transposon insertion in the promoter of the MFS1 gene, involved in drug efflux and multi-drug resistance. This new insert, however, does not confer an MDR phenotype to the strain.

Succinate dehydrogenase inhibitors (SDHIs) have played a crucial role in disease control to protect cereals as well as fruit and vegetables for more than a decade. Isoflucypram, the first representative of a newly installed subclass of SDHIs inside the Fungicide Resistance Action Committee (FRAC) family of complex II inhibitors, offers unparalleled long‐lasting efficacy against major foliar diseases in cereals. Herein we report the chemical optimization from early discovery towards isoflucypram and the first hypothesis of its altered binding mode in the ubiquinone binding site of succinate dehydrogenase. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Pyraziflumid is a novel succinate dehydrogenase inhibitor (SDHI) fungicide discovered and developed by Nihon Nohyaku Co., Ltd. It exhibits excellent fungicidal activities against a broad range of plant diseases and has a favorable safety profile for the Integrated Pest Management (IPM) program. This compound was found by researching the unique chemical derivatives, 3-(trifluoromethyl) pyrazine-2-carboxamides, and has good biological properties, such as preventive, residual and curative activity, and rain-fastness. Pyraziflumid was registered and launched in Japan in 2018. It was registered in South Korea in 2018 and is now under development in other countries. This paper describes the discovery, synthesis, biological activity, safety profile and mode of action of pyraziflumid. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) is caused by the ascomycete Zymoseptoria tritici and one of the predominating diseases in wheat (Triticum aestivum) in Europe. The control of STB is highly reliant on frequent fungicide applications. The primary objective of this study was to assess sensitivity levels of Z. tritici to different fungicide groups. The fungicides included in this study were epoxiconazole, prothioconazole-desthio, tebuconazole, and fluxapyroxad. A panel of 63 isolates from Estonia, Latvia, and Lithuania, and 10 isolates from Finland were tested. Fungicide sensitivity testing was carried out as a bioassay analyzing single pycnidium isolates on different fungicide concentrations. The average EC50 value in Baltic countries and Finland to epoxiconazole was high ranging from 1.04 to 2.19 ppm. For prothioconazole-desthio and tebuconazole, EC50 varied from 0.01 to 0.24 ppm, and 1.25 to 18.23 ppm, respectively. The average EC50 value for fluxapyroxad varied from 0.07 to 0.33 ppm. To explain the range of sensitivity, the samples were analyzed for CYP51 and Sdh mutations, as well as cytb G143A, CYP51 overexpression, and multidrug resistance (MDR). Frequencies of ZtCYP51 mutations D134G, V136A/C, A379G, I381V, and S524T in the Finnish-Baltic region were lower than in other European countries, but have increased compared to previous years. The frequency of cytb G143A conferring strobilurin resistance also augmented to 50–70% in the Z. tritici populations from Estonia, Finland, Latvia, and Lithuania. No Sdh mutations were found in this study, and neither strains of MDR phenotypes. However, we found a strain harboring a previously unknown transposon insertion in the promoter of the MFS1 gene, involved in drug efflux and multi-drug resistance. This new insert, however, does not confer an MDR phenotype to the strain. [ABSTRACT FROM AUTHOR]

Sensitivity of 24 isolates of Colletotrichum destructivum O'Gara, collected from alfalfa plants in Serbia, to eight selected fungicides, was investigated in this study. Molecular identification and pathogenicity test of isolates tested were also performed. Fungicide sensitivity was evaluated in vitro, using mycelial growth assay method. All isolates exhibited significant pathogenicity, causing necrosis at the alfalfa seedling root tips two days after inoculation. Using the primer pair GSF1-SR1 and by comparing the amplified fragments of the tested isolates with the marker (M), the presence of the amplicon of the expected size of about 900 bp was determined for all isolates. The isolates tested in this study showed different sensitivity towards fungicides in vitro. Mycelial growth was highly inhibited by QoI (quinone outside inhibitors) fungicide pyraclostrobin (mean EC50=0.39 µg mL−1) and by DMI (demethylation-inhibiting) fungicide tebuconazole (mean EC50=0.61 µg mL−1), followed by azoxystrobin (mean EC50=2.83 µg mL−1) and flutriafol (mean EC50=2.11 µg mL−1). Multi-site fungicide chlorothalonil and MBC (methyl benzimidazole carbamate) fungicide thiophanate-methyl evinced moderate inhibition with mean EC50=35.31 and 62.83 µg mL−1, respectively. Thirteen isolates were sensitive to SDHI (succinate dehydrogenase inhibitors) fungicide boscalid and fluxapyroxad, (mean EC50=0.49 and 0.19 µg mL−1, respectively), while the rest of isolates were highly resistant. [ABSTRACT FROM AUTHOR]

Fungicides are used to suppress the growth of fungi for crop protection. The most widely used fungicides are succinate dehydrogenase inhibitors (SDHIs) that act by blocking succinate dehydrogenase, the complex II of the mitochondrial electron transport chain. As recent reports suggested that SDHI-fungicides could not be selective for their fungi targets, we tested the mitochondrial function of human cells (Peripheral Blood Mononuclear Cells or PBMCs, HepG2 liver cells, and BJ-fibroblasts) after exposure for a short time to Boscalid and Bixafen, the two most used SDHIs. Electron Paramagnetic Resonance (EPR) spectroscopy was used to assess the oxygen consumption rate (OCR) and the level of mitochondrial superoxide radical. The OCR was significantly decreased in the three cell lines after exposure to both SDHIs. The level of mitochondrial superoxide increased in HepG2 after Boscalid and Bixafen exposure. In BJ-fibroblasts, mitochondrial superoxide was increased after Bixafen exposure, but not after Boscalid. No significant increase in mitochondrial superoxide was observed in PBMCs. Flow cytometry revealed an increase in the number of early apoptotic cells in HepG2 exposed to both SDHIs, but not in PBMCs and BJ-fibroblasts, results consistent with the high level of mitochondrial superoxide found in HepG2 cells after exposure. In conclusion, short-term exposure to Boscalid and Bixafen induces a mitochondrial dysfunction in human cells.

Ramularia leaf spot caused by the fungus Ramularia collo-cygni, has recently become widespread in Estonian barley fields. Currently, disease control in barley fields relies on SDHI and DMI fungicides, which might be threatened by R. collo-cygni isolates that are well-adapted to fungicide pressure. In a two-year study, 353 R. collo-cygni isolates were collected from spring barley fields in Estonia. A total of 153 R. collo-cygni isolates were examined for sensitivity to azoles (DMIs; prothioconazole-desthio, epoxiconazole, mefentrifluconazole) and succinate dehydrogenase inhibitors (SDHIs; boscalid, fluxapyroxad). Epoxiconazole was the least effective and a new fungicide mefentrifluconazole was the most effective DMI. Among SDHIs, fluxapyroxad was more effective than boscalid. Also, single R. collo-cygni isolates with high resistance to tested fungicides occurred, which could affect fungicide control of the pathogen. The entire collection of R. collo-cygni was analysed for mutations in fungicide target proteins. Six mutations were identified in CYP51 gene, the most dominant being I381T, I384T, and S459C. Also, numerous point mutations in the SdhC gene were present. The mutation G143A in strobilurin target protein CytB dominates in over 80% of the R. collo-cygni population, confirming the low efficacy of strobilurin fungicides in barley disease control.

Fusarium graminearum exhibited natural resistance to a majority of succinate dehydrogenase inhibitor fungicides (SDHIs) and the molecular mechanisms responsible for the natural resistance were still unknown. Succinate dehydrogenase subunit C ( SdhC ) is an essential gene for maintaining succinate-ubiquinone oxidoreductase (SQR) function in fungi. In F. graminearum , a paralog of FgSdhC named as FgSdhC 1 was identified. Based on RNA-Seq and qRT-PCR assay, we found that the expression level of FgSdhC 1 was very low but upregulated by SDHIs treatment. Based on reverse genetics, we demonstrated that FgSdhC 1 was an inessential gene in normal growth but was sufficient for maintaining SQR function and conferred natural resistance or reduced sensitivity toward SDHIs. Additionally, we found that the standard F. graminearum isolate PH-1 had high sensitivity to a majority of SDHIs. A single nucleotide variation (C to T) in the FgSdhC 1 of isolate PH-1, resulting in a premature termination codon (TAA) replacing the fourth amino acid glutamine (Q), led to the failure of FgSdhC 1 to perform functions of conferring nature resistance. These results established that a dispensable paralogous gene determined SDHIs resistance in natural populations of F. graminearum .

Developing environmentally friendly fungicides is crucial to tackle the issue of rising pesticide resistance. In this study, a series of novel pyrazole-4-carboxamide derivatives containing N -phenyl substituted amide fragments were designed and synthesized. The structures of target compounds were confirmed by 1 H NMR, 13 C NMR, and HRMS, and the crystal structure of the most active compound N -(1-(4-(4-( tert -butyl)benzamido)phenyl)propan-2-yl)-3-(difluoromethyl)- N -methoxy-1-methyl-1 H -pyrazole-4-carboxamide ( U22 ) was further determined by X-ray single-crystal diffraction. The bioassay results indicated that the 26 target compounds possessed good in vitro antifungal activity against Sclerotinia sclerotiorum with EC 50 values for compounds U12 , U13 , U15 , U16 , U18 , U22 , and U23 being 4.17 ± 0.46, 8.04 ± 0.71, 7.01 ± 0.71, 12.77 ± 1.00, 8.11 ± 0.70, 0.94 ± 0.11, and 9.48 ± 0.83 μg·mL -1 , respectively, which were the similar to controls bixafen (6.70 ± 0.47 μg·mL -1 ), fluxapyroxad (0.71 ± 0.14 μg·mL -1 ), and pydiflumetofen (0.06 ± 0.01 μg·mL -1 ). Furthermore, in vivo antifungal activity results against S. sclerotiorum indicated that compounds U12 (80.6%) and U22 (89.9%) possessed excellent preventative efficacy at 200 μg·mL -1 , which was the same as the control pydiflumetofen (82.4%). Scanning electron microscopy and transmission electron microscopy studies found that the compound U22 could destroy the hyphal morphology and damage mitochondria, cell membranes, and vacuoles. The results of molecular docking of compound U22 and pydiflumetofen with succinate dehydrogenase (SDH) indicated they interact well with the active site of SDH. This study validated our approach and design strategy to produce compounds with an enhanced biological activity as compared to the parent structure.

Fluxapyroxad, a type of succinate dehydrogenase inhibitor fungicide, has been used to control the growth of gray mold on strawberry for more than 5 years in China. Selection for resistance to the causal agent Botrytis cinerea became a threat to the efficacy of fluxapyroxad. In total, 160 B. cinerea isolates collected from Shanghai during 2020 and 2021 were tested for their resistance to fluxapyroxad using mycelial growth inhibition. The results indicated that the curve of baseline sensitivity was unimodal, with an approximately normal distribution and a mean effective concentration of the fungicide that inhibited growth by 50% (EC 50 ) of 0.18 ± 0.01 μg/ml. In total, 27.78 and 48.57% of isolates were resistant to fluxapyroxad in 2020 and 2021, respectively, where the lowest EC 50 value of mycelial growth inhibition was 0.03 μg/ml and the highest value was 51.3 μg/ml. Resistance mechanism analysis showed that the succinate dehydrogenase subunit B ( SdhB ) N230I mutation could lead to resistance and P225F mutation could lead to higher resistance. These data suggest that the resistance frequency of B. cinerea isolates to fluxapyroxad increased in 2021 compared with 2020, which requires appropriate fungicide rotation strategies to be implemented in order to control gray mold on strawberry in the future., Competing Interests: The author(s) declare no conflict of interest.

Résumé Chez l'homme, les dysfonctions des enzymes du cycle de Krebs liées à des mutations causent des encéphalopathies sévères du jeune enfant, ou différents types de tumeurs et de cancers touchant différents organes. Ainsi des mutations des gènes de la succinate-déshydrogénase ont été identifiées dans des formes familiales de phéochromocytomes et paragangliomes. Les mutations du gène de la fumarase s'observent dans des léiomyomes utérins en association avec des cancers rénaux, mais des cas d'encéphalopathies de l'enfant ont aussi été observés. Les mutations des gènes de l'isocitrate-déshydrogénase peuvent représenter jusqu'à 20% des leucémies myéloïdes aiguës et jusqu'à 80% dans certains gliomes. On ne sait actuellement expliciter la diversité des conséquences possibles de ces mutations : encéphalopathies versus cancers, nature des tissus affectés, cinétique variable d'apparition des symptômes. Il semble en revanche établi que les anomalies dans les équilibres métaboliques qui résultent de ces mutations soient à la base des processus tumoraux en modulant l'activité d'hydroxylases susceptibles d'affecter certains facteurs de transcriptions, mais aussi la méthylation de l'ADN et les histones. Dans ce contexte, il semble étonnant que soient largement utilisés certains fongicides dont l'effet est de bloquer une étape centrale du cycle de Krebs, la succinate-déshydrogénase. Le principe de précaution voudrait sans aucun doute de réévaluer urgemment la nécessité de l'usage de telles substances pour l'homme et l'environnement. In humans, dysfunctions of Krebs cycle enzymes caused by genetic mutations result either in severe encephalopathies of the young child, or in the appearance of different types of tumors and cancers affecting diverse organs. Thus mutations of the succinate dehydrogenase genes have been identified in familial forms of pheochromocytomas and paragangliomas. Most of the mutations in the fumarase gene are found in uterine leiomyomas in association with renal cancers, but cases of childhood encephalopathies have also been observed resulting from mutations affecting the same gene. Isocitrate dehydrogenase gene mutations account for up to 20% of acute myeloid leukemias, and up to 80% in some gliomas. So far we cannot explain the diversity of the possible consequences of these mutations : encephalopathies versus cancers, the different tissues that are affected and the variable kinetics of appearance of symptoms. On the other hand, it seems now established that the abnormalities in the metabolic equilibria that result from these mutations are at the basis of the tumor processes by modulating the activity of a number of hydroxylases that may affect the fate of certain transcription factors, but also the DNA and histone methylation. In this context, it seems surprising that some fungicides that are now widely used, block a central stage of the Krebs cycle, namely the succinate dehydrogenase. The principle of precaution would impose to urgently re-evaluate the need for the use of these substances in consideration of human health and the environment. [ABSTRACT FROM AUTHOR]

Strains of Phakopsora pachyrhizi with a lower SDHI sensitivity have been found for the first time in monitoring studies in the season 2015-2016. Such strains needed to be characterized with respect to the underlying mechanism and for the development of a molecular genetic monitoring method. A mutation in the SdhCgene, which causes the amino acid substitution C-I86F, was identified in strains with a lower SDHI sensitivity. A species-specific real-time PCR for the detection and quantification of alleles which cause C-I86F exchange in diseased plant tissue was developed. The frequency of C-I86F was highest when samples were first selected on SDHI-treated detached leaves, and there was * 50% mutated allele. The SDHIs included in this study were affected to a greater or lesser extent by C-I86F in detached leaf assays. This is the first report of a causal resistance mechanism toward SDHIs in P. pachyrhizi. The practical relevance of the C-I86F exchange on the field efficacy of SDHI containing fungicides needs further investigation. [ABSTRACT FROM AUTHOR]

Pyraziflumid was discovered as a novel SDHI fungicide chemically characterized by the 3-(trifluoromethyl)pyrazine-2-carboxamide group. This chemical series showed particularly high fungicidal activities against a broad spectrum of plant diseases in the case of N-(biphenyl-2-yl) as well as N-(1,1,3-trimethylindan-4-yl)carboxamides. Various N-(biphenyl-2-yl)pyrazine-2-carboxamides were synthesized, and their structure-activity relationships were studied. The optimization of the fungicidal performance of the series finally led to the identification of pyraziflumid, which could control a wide range of plant diseases. In this report, details of the structure-activity relationships from the lead compound to pyraziflumid are described. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) caused by the fungal pathogen Zymoseptoria tritici is a global threat to sustainable wheat production. Applications of fungicide against STB are regarded as an essential means to minimise yield losses, however, fungicide resistance is developing and affecting fungicide efficacy greatly. Only a few fungicide classes are available for STB control. DMI fungicides are seen as the main group, but increasing problems with resistance is challenging their use. In 2015 and 2016, field trials were conducted testing fungicide spray strategies using one, two or three applications, alternations, mixtures of different DMIs and DMI mixed with other modes of action including a SDHI and a multi-site inhibitor. The strategies were tested for disease control, their impact on yield and their effect on resistance build-up, measured as CYP51 alterations responsible for decreased sensitivity and efficacy of DMIs. Strategies consisting of three treatments provided adequate control of STB and significant yield increases. The best results with regard to yield and control were attained by a diversified DMI strategy also including the SDHI boscalid and the multi-site inhibitor folpet. Spraying once or twice lowered selection yet compromised STB control and yield. CYP51 alteration I381V was the most predominated in all samples. Frequencies of alterations D134G, V136A and S524T increased significantly following applications with DMI fungicides. The more diversified a strategy, the less it selected for CYP51 alterations. EC 50 values for epoxiconazole showed a tendency to be higher post-treatment in 2015. The results presented in this study encourage the adoption of mixing and alternating fungicides into spray strategies to minimise the risk of resistance build-up and to prolong the effective life of fungicides. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) or scab mainly caused by Fusarium asiaticum is a devastating fungal disease in wheat. In China, carbendazim (MBC) and its co-formulated mixture with other fungicides are the main fungicides for controlling the disease. But resistant populations have developed severely in the field. The fungicides for controlling the disease are limited. So screening novel fungicides for controlling FHB is urgent. The fungicide pydiflumetofen (development code number: SYN545974),3-(Difluoromethyl) N-methyl-N-[1-methyl-2-(2,4,6-trichlorophenyl)ethyl]-1H-pyrazole-4-carboxami.d.e, is a novel succinate dehydrogenase inhibitor (SDHI) that was developed by Syngenta. In this study, the baseline sensitivities for different isolates of F. asiaticum from various regions of China to pydiflumetofen were established. The 50% effective concentration (EC 50 ) value of pydiflumetofen on suppressing mycelial growth against 116 isolates of F. asiaticum was 0.019–0.2084 μg/ml and their average value was 0.0745 ± 0.0367 μg/ml. The EC 50 value of pydiflumetofen on suppressing conidium germination was 0.0583–0.4237 μg/ml and their average value was 0.1813 ± 0.0861 μg/ml. The results indicated that the fungicide had strong inhibition effect on mycelial growth and conidium germination against F. asiaticum in vitro . The EC 50 values distribution of 116 isolates measured by mycelial growth assay or by conidium germination assay was a unimodal curve and could be used for detecting any sensitivity changes of F. asiaticum populations to pydiflumetofen in the future. The results of cross-resistance analysis indicated that there was no positive or negative cross-resistance between pydiflumetofen and carbendazim/phenamacril. In field trials, though FHB was very severe, pydiflumetofen at 125, 150 and 200 g ai ha −1 all provided more than 80% control efficacy which was significantly higher than that of phenamacril at 375 g ai ha −1 or MBC at 600 g ai ha −1 in 2015 and 2016. In conclusion, pydiflumetofen had very high activity against F. asiaticum in vitro and excellent efficacy for controlling FHB could also manage carbendazim-resistant F. asiaticum populations in the field. [ABSTRACT FROM AUTHOR]