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Qo Inhibitors (qo + inhibitor)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Rapid method for detecting resistance to a QoI fungicide in Plasmopara viticola populations

PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 8 2009
Seiichi Furuya
Abstract BACKGROUND: The increasing occurrence of Qo inhibitor (QoI)-fungicide-resistant Plasmopara viticola (Berk. & MA Curtis) Berl. & DeToni populations is becoming a serious problem in the control of grapevine downy mildew worldwide. RESULTS: The authors have developed a rapid method for detecting resistance to a QoI fungicide, azoxystrobin, in P. viticola populations using the nested PCR-RFLP method. With this method, a glycine-to-alanine substitution was discovered at codon 143 in the cytochrome b gene of P. viticola populations found in Japan. CONCLUSION: It is proposed that the nested PCR-RFLP method is a high-speed, sensitive and reliable tool for detecting azoxystrobin-resistant P. viticola populations. Copyright © 2009 Society of Chemical Industry [source]

Modeling the Qo site of crop pathogens in Saccharomyces cerevisiae cytochrome b

FEBS JOURNAL, Issue 11 2004
Nicholas Fisher
Saccharomyces cerevisiae has been used as a model system to characterize the effect of cytochrome b mutations found in fungal and oomycete plant pathogens resistant to Qo inhibitors (QoIs), including the strobilurins, now widely employed in agriculture to control such diseases. Specific residues in the Qo site of yeast cytochrome b were modified to obtain four new forms mimicking the Qo binding site of Erysiphe graminis, Venturia inaequalis, Sphaerotheca fuliginea and Phytophthora megasperma. These modified versions of cytochrome b were then used to study the impact of the introduction of the G143A mutation on bc1 complex activity. In addition, the effects of two other mutations F129L and L275F, which also confer levels of QoI insensitivity, were also studied. The G143A mutation caused a high level of resistance to QoI compounds such as myxothiazol, axoxystrobin and pyraclostrobin, but not to stigmatellin. The pattern of resistance conferred by F129L and L275F was different. Interestingly G143A had a slightly deleterious effect on the bc1 function in V. inaequalis, S. fuliginea and P. megasperma Qo site mimics but not in that for E. graminis. Thus small variations in the Qo site seem to affect the impact of the G143A mutation on bc1 activity. Based on this observation in the yeast model, it might be anticipated that the G143A mutation might affect the fitness of pathogens differentially. If so, this could contribute to observed differences in the rates of evolution of QoI resistance in fungal and oomycete pathogens. [source]

Mechanisms influencing the evolution of resistance to Qo inhibitor fungicides,,

PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 9 2002
Ulrich Gisi
Abstract Fungicides inhibiting the mitochondrial respiration of plant pathogens by binding to the cytochrome bc1 enzyme complex (complex III) at the Qo site (Qo inhibitors, QoIs) were first introduced to the market in 1996. After a short time period, isolates resistant to QoIs were detected in field populations of a range of important plant pathogens including Blumeria graminis Speer f sp tritici, Sphaerotheca fuliginea (Schlecht ex Fr) Poll, Plasmopara viticola (Berk & MA Curtis ex de Bary) Berl & de Toni, Pseudoperonospora cubensis (Berk & MA Curtis) Rost, Mycosphaerella fijiensis Morelet and Venturia inaequalis (Cooke) Wint. In most cases, resistance was conferred by a point mutation in the mitochondrial cytochrome b (cyt b) gene leading to an amino-acid change from glycine to alanine at position 143 (G143A), although additional mutations and mechanisms have been claimed in a number of organisms. Transformation of sensitive protoplasts of M fijiensis with a DNA fragment of a resistant M fijiensis isolate containing the mutation yielded fully resistant transformants, demonstrating that the G143A substitution may be the most powerful transversion in the cyt b gene conferring resistance. The G143A substitution is claimed not to affect the activity of the enzyme, suggesting that resistant individuals may not suffer from a significant fitness penalty, as was demonstrated in B graminis f sp tritici. It is not known whether this observation applies also for other pathogen species expressing the G143A substitution. Since fungal cells contain a large number of mitochondria, early mitotic events in the evolution of resistance to QoIs have to be considered, such as mutation frequency (claimed to be higher in mitochondrial than nuclear DNA), intracellular proliferation of mitochondria in the heteroplasmatic cell stage, and cell to cell donation of mutated mitochondria. Since the cyt b gene is located in the mitochondrial genome, inheritance of resistance in filamentous fungi is expected to be non-Mendelian and, therefore, in most species uniparental. In the isogamous fungus B graminis f sp tritici, crosses of sensitive and resistant parents yielded cleistothecia containing either sensitive or resistant ascospores and the segregation pattern for resistance in the F1 progeny population was 1:1. In the anisogamous fungus V inaequalis, donation of resistance was maternal and the segregation ratio 1:0. In random mating populations, the sex ratio (mating type distribution) is generally assumed to be 1:1. Therefore, the overall proportion of sensitive and resistant individuals in unselected populations is expected to be 1:1. Evolution of resistance to QoIs will depend mainly on early mitotic events; the selection process for resistant mutants in populations exposed to QoI treatments may follow mechanisms similar to those described for resistance controlled by single nuclear genes in other fungicide classes. It will remain important to understand how the mitochondrial nature of QoI resistance and factors such as mutation, recombination, selection and migration might influence the evolution of QoI resistance in different plant pathogens. © 2002 Society of Chemical Industry [source]

Sensitivity of Botrytis cinerea from vegetable greenhouses to boscalid

PLANT PATHOLOGY, Issue 4 2007
C. Q. Zhang
Between 2004 and 2006, 228 isolates of Botrytis cinerea from two regions in China were characterized for baseline sensitivity to boscalid, a new active ingredient that interferes with succinate ubiquinone reductase in the electron transport chain. The isolates showed similar sensitivity in different years and regions. Baseline sensitivities were distributed as unimodal curves with mean EC50 values of 1·07 (± 0·11) and 0·42 (± 0·05) mg L,1 for inhibition of mycelial growth and conidial germination, respectively. Laboratory studies were conducted to evaluate the risk of development of resistance to boscalid. Boscalid-resistant mutants were obtained by UV-treatment at lower frequencies and with smaller resistance factors than pyrimethanil-resistant mutants. All boscalid-resistant mutants were also significantly more sensitive to Qo inhibitors than their wild-type parents and showed reduced sporulation in vitro and pathogenicity on aubergine leaves. The results suggested that the risk of resistance developing for boscalid was lower than for pyrimethanil. However, as B. cinerea is a high-risk pathogen, appropriate precautions against resistance development should be taken. Synergism between the activity of boscalid and that of kresoxim-methyl was observed. [source]