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Pierre Leroux - One of the best experts on this subject based on the ideXlab platform.
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First occurrence of resistance to Strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains.
Pest management science, 2009Co-Authors: Anne Sophie Walker, Christiane Auclair, Michel Gredt, Pierre LerouxAbstract:BACKGROUND:Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of Strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to Strobilurins of French isolates of Microdochium and to characterise the possible mechanisms of resistance. RESULTS: Half of the strains collected in 2007 were resistant to Strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross-resistance was observed between all Strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of Strobilurins. Two other mechanisms were also detected at lower frequencies. CONCLUSION: This is the first report of Strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account. Copyright © 2009 Society of Chemical Industry
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First occurrence of resistance to Strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains
Pest Management Science, 2009Co-Authors: Anne Sophie Walker, Christiane Auclair, Michel Gredt, Pierre LerouxAbstract:BACKGROUND: Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of Strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to Strobilurins of French isolates of Microdochium and to characterise the possiblemechanisms of resistance. RESULTS: Half of the strains collected in 2007 were resistant to Strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross-resistance was observed between all Strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of Strobilurins. Two othermechanismswere also detected at lower frequencies. CONCLUSION: This is the first report of Strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account.
Wolfram Köller - One of the best experts on this subject based on the ideXlab platform.
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Managing Resistance of Venturia inaequalis to the Strobilurin Fungicides
Plant Health Progress, 2004Co-Authors: William W. Turechek, Wolfram KöllerAbstract:Over the past thirty years, fungicide resistance has been cited as the cause of large-scale crop losses due to apple scab in a number of commercial orchards in the Northeast. The Strobilurins represent the most recent class of fungicides for which the threat of resistance exists. In this article we examine the use of Strobilurin fungicides at their highest and lowest labeled rates and as a mixture of the lowest labeled rate with a protectant fungicide in commercial spray programs for efficacy against apple scab as well as their utility in a resistance management program. Our results suggest that anti-resistance properties of high Strobilurin rates are superior to low rates and low rate mixtures with a protectant fungicide.
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Characterization of laboratory mutants of Venturia inaequalis resistant to the Strobilurin-related fungicide kresoxim-methyl.
Current genetics, 2000Co-Authors: Desen Zheng, Gilberto Olaya, Wolfram KöllerAbstract:Several agricultural fungicides related to the antifungal Strobilurins act as inhibitors of respiration by binding to mitochondrial cytochrome b. Two types of laboratory mutants resisting higher doses of the Strobilurin-related inhibitor kresoxim-methyl were characterized for Venturia inaequalis, the causal agent of apple scab. Selection of mutagenized conidia by kresoxim-methyl yielded mutants altered in the expression of alternative respiration during the stage of conidia germination. Cytochrome b sequences were not affected in the respective mutants. Selection of conidia on media containing the alternative oxidase inhibitor salicylhydroxamic acid in addition to kresoxim-methyl yielded a highly resistant mutant distinguished by a G143A exchange in cytochrome b. The status of mitochondrial cytochrome b genes remained heteroplasmic, and mitochondria containing wild-type cytochrome b returned to high frequencies during cultivation on inhibitor-free medium. However, continuation of the selection process led to a more pronounced replacement of sensitive by mutated mitochondria. The G143A mutation of cytochrome b causing resistance of V. inaequalis to a Strobilurin-related inhibitor has been reported previously for mouse mitochondria; and a permanent G143A exchange rendering naturally resistant mitochondria has been reported for the Strobilurin-producing basidiomycete Mycena galopoda and for the sea urchin Paracentrotus lividus. At the corresponding position, alanine was also present in chloroplast cytochrome b6 exhibiting low binding of Strobilurin-related inhibitors. The mutation of cytochrome b reported here for V. inaequalis describes the first example of a mutation in filamentous ascomycetes and is part of an assessment of resistance risks inherent to Strobilurin fungicides.
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CHARACTERIZATION OF THE MITOCHONDRIAL CYTOCHROME B GENE FROM VENTURIA INAEQUALIS
Current Genetics, 1997Co-Authors: Desen Zheng, Wolfram KöllerAbstract:A new class of agricultural fungicides derived from the group of antifungal Strobilurins acts as specific respiration inhibitors by binding to mitochondrial cytochrome b. The cytochrome b gene was cloned and sequenced from the mitochondrial genome of Venturia inaequalis, the causal agent of apple scab. The gene was 10.65 kbp in size and contained seven exons and six introns. The exons encoded a protein of 393 amino acids. Comparison of the deduced amino-acid sequence with cytochrome b proteins from other fungi revealed highest homologies to the respective proteins of Aspergillus nidulans, Podospora anserina and Neurospora crassa. All amino acids of the V. inaequalis cytochrome b at positions altered in mutants of Saccharomyces cerevisiae resistant to Strobilurins, and other fungi with reduced sensitivities to Strobilurins, were identical to wild-type isolates of several fungi. The cloning and characterization of the V. inaequalis cytochrome b gene is the initial step in the assessment of resistance risks inherent to the Strobilurin fungicides.
Anne Sophie Walker - One of the best experts on this subject based on the ideXlab platform.
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First occurrence of resistance to Strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains.
Pest management science, 2009Co-Authors: Anne Sophie Walker, Christiane Auclair, Michel Gredt, Pierre LerouxAbstract:BACKGROUND:Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of Strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to Strobilurins of French isolates of Microdochium and to characterise the possible mechanisms of resistance. RESULTS: Half of the strains collected in 2007 were resistant to Strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross-resistance was observed between all Strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of Strobilurins. Two other mechanisms were also detected at lower frequencies. CONCLUSION: This is the first report of Strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account. Copyright © 2009 Society of Chemical Industry
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First occurrence of resistance to Strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains
Pest Management Science, 2009Co-Authors: Anne Sophie Walker, Christiane Auclair, Michel Gredt, Pierre LerouxAbstract:BACKGROUND: Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of Strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to Strobilurins of French isolates of Microdochium and to characterise the possiblemechanisms of resistance. RESULTS: Half of the strains collected in 2007 were resistant to Strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross-resistance was observed between all Strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of Strobilurins. Two othermechanismswere also detected at lower frequencies. CONCLUSION: This is the first report of Strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account.
Derek W Hollomon - One of the best experts on this subject based on the ideXlab platform.
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a critical evaluation of the role of alternative oxidase in the performance of Strobilurin and related fungicides acting at the qo site of complex iii
Pest Management Science, 2003Co-Authors: Paul M Wood, Derek W HollomonAbstract:Mitochondrial respiration conserves energy by linking NADH oxidation and electron-coupled proton translocation with ATP synthesis, through a core pathway involving three large protein complexes. Strobilurin fungicides block electron flow through one of these complexes (III), and disrupt energy supply. Despite an essential need for ATP throughout fungal disease development, Strobilurins are largely preventative; indeed some diseases are not controlled at all, and several pathogens have quickly developed resistance. Target-site variation is not the only cause of these performance difficulties. Alternative oxidase (AOX) is a Strobilurin-insensitive terminal oxidase that allows electrons from ubiquinol to bypass Complex III. Its synthesis is constitutive in some fungi but in many others is induced by inhibition of the main pathway. AOX provides a Strobilurin-insensitive pathway for oxidation of NADH. Protons are pumped as electrons flow through Complex I, but energy conservation is less efficient than for the full respiratory chain. Salicylhydroxamic acid (SHAM) is a characteristic inhibitor of AOX, and several studies have explored the potentiation of Strobilurin activity by SHAM. We present a kinetic-based model which relates changes in the extent of potentiation during different phases of disease development to a changing importance of energy efficiency. The model provides a framework for understanding the varying efficacy of Strobilurin fungicides. In many cases, AOX can limit Strobilurin effectiveness once an infection is established, but is unable to interfere significantly with Strobilurin action during germination. A less stringent demand for energy efficiency during early disease development could lead to insensitivity towards this class of fungicides. This is discussed in relation to Botrytis cinerea, which is often poorly controlled by Strobilurins. Mutations with a similar effect may explain evidence implicating AOX in resistance development in normally well-controlled plant pathogens, such as Venturia inaequalis.
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following the dynamics of Strobilurin resistance in blumeria graminis f sp tritici using quantitative allele specific real time pcr measurements with the fluorescent dye sybr green i
Plant Pathology, 2002Co-Authors: B A Fraaije, J A Butters, J M Coelho, D R Jones, Derek W HollomonAbstract:Strobilurin-resistant isolates of Blumeria (Erysiphe) graminis f.sp. tritici, the cause of wheat powdery mildew, were more than 10-fold less sensitive to azoxystrobin than sensitive isolates. In all resistant isolates, a mutation resulting in the replacement of a glycine by an alanine residue at codon 143 (G143A) in the mitochondrial cytochrome b gene was found. Allele-specific primers were designed to detect this point mutation in infected wheat leaves. Using quantitative fluorescent allele-specific real-time polymerase chain reaction (PCR) measurements, Strobilurin-resistant A143 alleles could be detected amongst Strobilurin-sensitive G143 alleles at a frequency of at least 1 in 10 000, depending on the amount of target and nontarget DNA. Most isolates tested were dominant homoplasmic for either the A143 or G143 allele, although mixed populations of alleles could be detected in some isolates. In some of these isolates, Strobilurin resistance was not always stable when they were maintained for many generations in the absence of selection. The allele-specific real-time PCR assay was also used to follow the dynamics of A143 alleles in field populations of B. graminis f.sp. tritici before and after application of fungicides. As expected, the A143 allele frequency only increased under selection pressure from a Strobilurin fungicide. After three sprays of azoxystrobin, a pronounced selection for the Strobilurin-resistant allele, with an increase in average frequency from 2·2 to 58%, was measured. The use of quantitative real-time PCR diagnostics for early detection of fungicide resistance genes at low frequency, coupled with risk evaluation, will be invaluable for further resistance risk assessment and validation of antiresistance strategies.
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occurrence and molecular characterization of Strobilurin resistance in cucumber powdery mildew and downy mildew
Phytopathology, 2001Co-Authors: Hideo Ishii, B A Fraaije, T Sugiyama, K Noguchi, K Nishimura, T Takeda, T Amano, Derek W HollomonAbstract:Ishii, H., Fraaije, B. A., Sugiyama, T., Noguchi, K., Nishimura, K., Takeda, T., Amano, T., and Hollomon, D. W. 2001. Occurrence and molecular characterization of Strobilurin resistance in cucumber powdery mildew and downy mildew. Phytopathology 91:1166-1171. Between 1998 and 1999, control failure of powdery mildew (Podosphaera fusca) and downy mildew (Pseudoperonospora cubensis) by the Strobilurin fungicides azoxystrobin and kresoxim-methyl was observed in cucumber-growing areas of Japan. Results from inoculation tests carried out on intact cucumber plants and leaf disks clearly showed the distribution of pathogen isolates highly resistant to azoxystrobin and kresoximmethyl. Fragments of the fungicide-targeted mitochondrial cytochrome b gene were polymerase chain reaction amplified from total pathogen DNA and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochrome b gene, resulting in substitution of glycine by alanine at position 143, was found in resistant isolates of downy mildew. This substitution in cytochrome b seemed to result in high resistance to Strobilurins in this pathogen. The same mutation was found in some but not all resistant isolates of powdery mildew. This study suggests that a mutation at position 143 in the target-encoding gene, resulting in an amino acid substitution, was probably a major cause of the rapid development of high Strobilurin resistance in these two pathogens.
Amedeo Reyneri - One of the best experts on this subject based on the ideXlab platform.
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effect of fungicide and foliar fertilizer application to winter wheat at anthesis on flag leaf senescence grain yield flour bread making quality and don contamination
European Journal of Agronomy, 2009Co-Authors: Massimo Blandino, Amedeo ReyneriAbstract:Abstract In this study, field experiments have been conducted over three growing seasons to evaluate the effect of fungicides (triazoles and Strobilurins) and a foliar fertilizer application to winter wheat at anthesis on flag leaf senescence, grain yield, bread-making quality, Fusarium head blight (FHB) disease and deoxynivalenol (DON) contamination. Flag leaf greenness was significantly influenced by the fungicide application. A delay in flag leaf senescence following triazole use did not increase grain yield. No effects of fungicide application on protein concentration were recorded. The application of Strobilurin to a triazole programme did not significantly delay senescence of the flag leaf or increased yield, compared to the triazole-only application, while a consistent benefit was observed for dough strength ( W ). The triazole application led to significantly lower FHB symptoms and DON contamination, while the triazole-Strobilurin fungicides programme led to an increase in DON contents, that were often higher than the untreated controls. Grain yield and quality were improved when a foliar feed containing macro- and micro-nutrients was added to a triazole fungicide programme, with no additional risk for DON contamination. Compared to the Strobilurin fungicide application, the foliar fertilizer led to a longer delay of the flag leaf senescence and higher bread-making quality.
