Abstract:Gray leaf spot caused by Pyricularia grisea is a highly destructive disease of perennial ryegrass turf. Control of gray leaf spot is dependent on the use of preventative fungicide treatments. Strobilurin-based (Q(o)I) fungicides, which inhibit the cytochrome bc(1) respiratory complex, have proven to be very effective against gray leaf spot. However, in August 2000, disease was diagnosed in Q(o)I-treated perennial ryegrass turf on golf courses in Lexington, KY, Champaign, IL, and Bloomington, IL. To determine i… Show more
“…1) binds with a hydrogen bond to the amide group of glutamic acid at position 272 in domain C; therefore, this region plays an important role in accepting fungicides. Since substitution of glycine for alanine at position 143 (G143A) in domain B significantly lowers the affinity of strobilurin fungicides to cytochrome b, 7,8,13,14,[19][20][21][22][23] interaction between domain B and strobilurin fungicides must be strong. On the other hand, substitution of phenylalanine for leucine at position 129 (F129L) in domain A has been shown not to significantly lower the affinity of strobilurin fungicides to cytochrome b.…”
Section: Discussionmentioning
confidence: 99%
“…On the other hand, substitution of phenylalanine for leucine at position 129 (F129L) in domain A has been shown not to significantly lower the affinity of strobilurin fungicides to cytochrome b. 14,21) This suggests that interaction between domain A and strobilurin fungicides might be rather weak. The result obtained here that strobilurin fungicides inhibited SCR activities of crops, rats and carp rather potently, which have different amino acid residues from those of fungi at position 130 in domain A (Fig.…”
Pyribencarb is a novel benzylcarbamate-type fungicide, which is active against a wide range of plant pathogenic fungi. In this paper, the inhibitory effects of this fungicide on the electron transport system of fungi, plants, rat and carp were examined to elucidate its mode of action and selectivity. Pyribencarb potently inhibited succinatecytochrome c reductase (SCR) activities of Botrytis cinerea (cucumber gray mold), Corynespora cassiicola (leaf spot) and decylubiquinol-cytochrome c reductase (UCR) activity of B. cinerea. Pyribencarb inhibited the UCR of B. cinerea in an uncompetitive manner with respect to decylubiquinol, which was the same as strobilurin fungicides, and the substrate-dependent inhibition constant was found from calculation to be 13 nM. These results suggested that the target site of pyribencarb is cytochrome b of complex III in the electron transport system of the respiratory chain. On the other hand, the inhibitory potency of pyribencarb on SCR activities of plants, rats and carp was relatively weak compared with that of strobilurin fungicides, indicating that pyribencarb is a Qo inhibitor of cytochrome b, whose properties are superior to well-known Qo inhibitor fungicides in terms of target. The binding site of pyribencarb on cytochrome b was assumed to be a little different from that of strobilurin fungicides, because pyribencarb inhibited SCRs of strobilurin fungicide-resistant strains of B. cinerea and C. cassiicola with relatively low concentrations. The binding site was also discussed through comparison of amino acid sequences of plants, rats, carp, yeast and fungi, including B. cinerea, which was elucidated in this paper.
“…1) binds with a hydrogen bond to the amide group of glutamic acid at position 272 in domain C; therefore, this region plays an important role in accepting fungicides. Since substitution of glycine for alanine at position 143 (G143A) in domain B significantly lowers the affinity of strobilurin fungicides to cytochrome b, 7,8,13,14,[19][20][21][22][23] interaction between domain B and strobilurin fungicides must be strong. On the other hand, substitution of phenylalanine for leucine at position 129 (F129L) in domain A has been shown not to significantly lower the affinity of strobilurin fungicides to cytochrome b.…”
Section: Discussionmentioning
confidence: 99%
“…On the other hand, substitution of phenylalanine for leucine at position 129 (F129L) in domain A has been shown not to significantly lower the affinity of strobilurin fungicides to cytochrome b. 14,21) This suggests that interaction between domain A and strobilurin fungicides might be rather weak. The result obtained here that strobilurin fungicides inhibited SCR activities of crops, rats and carp rather potently, which have different amino acid residues from those of fungi at position 130 in domain A (Fig.…”
Pyribencarb is a novel benzylcarbamate-type fungicide, which is active against a wide range of plant pathogenic fungi. In this paper, the inhibitory effects of this fungicide on the electron transport system of fungi, plants, rat and carp were examined to elucidate its mode of action and selectivity. Pyribencarb potently inhibited succinatecytochrome c reductase (SCR) activities of Botrytis cinerea (cucumber gray mold), Corynespora cassiicola (leaf spot) and decylubiquinol-cytochrome c reductase (UCR) activity of B. cinerea. Pyribencarb inhibited the UCR of B. cinerea in an uncompetitive manner with respect to decylubiquinol, which was the same as strobilurin fungicides, and the substrate-dependent inhibition constant was found from calculation to be 13 nM. These results suggested that the target site of pyribencarb is cytochrome b of complex III in the electron transport system of the respiratory chain. On the other hand, the inhibitory potency of pyribencarb on SCR activities of plants, rats and carp was relatively weak compared with that of strobilurin fungicides, indicating that pyribencarb is a Qo inhibitor of cytochrome b, whose properties are superior to well-known Qo inhibitor fungicides in terms of target. The binding site of pyribencarb on cytochrome b was assumed to be a little different from that of strobilurin fungicides, because pyribencarb inhibited SCRs of strobilurin fungicide-resistant strains of B. cinerea and C. cassiicola with relatively low concentrations. The binding site was also discussed through comparison of amino acid sequences of plants, rats, carp, yeast and fungi, including B. cinerea, which was elucidated in this paper.
“…Mutations mediating a G143A-or a F129L exchange lead to complete loss or drastic reduction of fungicide efficacies (26,31). Single spore isolates of the apple powdery mildew Podosphaera leucotricha collected from commercial orchards were all heteroplasmic with respect to their mitochondrial cytochrome b gene and differed in strobilurin sensitivity.…”
Section: Qualitative and Quantitative Fungicide Resistancementioning
In this review article, we show that occurrence of fungicide resistance is one of the most important issues in modern agriculture. Fungicide resistance may be due to mutations of genes encoding fungicide targets (qualitative fungicide resistance) or to different mechanisms that are induced by sub-lethal fungicide stress. These mechanisms result in different and varying levels of resistance (quantitative fungicide resistance). We discuss whether or not extensive use of fungicides in agricultural environments is related to the occurrence of fungicide resistance in clinical environments. Furthermore, we provide recommendations of how development of fungicide resistant pathogen populations may be prevented or delayed.
“…33,34) The mutation at codon 129 (TTC→ TTA) is associated with moderate resistance, and mutation at codon 143 (GGT→ GCT) is associated with resistance. 34) In Taiwan, rice blast is endemic to the first rice cultivation (March to June), affecting over 20,000 ha each year. 35) Previous studies showed the presence of more than 20 races of M. oryzae by the standard lines of rice.…”
Magnaporthe oryzae (Anamorph: Pyricularia oryzae), the causal agent of rice blast disease, is the major pathogen that reduces the yield of rice worldwide. Melanin biosynthesis inhibitors (MBIs) and strobilurins (QoIs) are common fungicides used to control the disease. One hundred and three M. oryzae isolates from different rice-production areas in Taiwan were evaluated for their molecular phylogeny and sensitivity to MBI and QoI fungicides. Molecular phylogenetic analysis showed that all M. oryzae isolates could be classified into nine genetic groups (A-I) based on the DNA polymorphism amplified by CNS1/MP primers. Predominant ones are groups A (72 isolates) and B (15 isolates). Fungicide tests showed that M. oryzae isolates were sensitive to MBIs (carpropamid and tricyclazole) and less sensitive to QoIs (kresoxim-methyl and azoxystrobin). Amplifying the cytochrome b (cyt b) gene revealed that isolates with low sensitivity to QoIs did not correspond with mutation at codon 129 or 143 in the cyt b gene.
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