Monitoring of the Sensitivity of Magnaporthe grisea to Metominostrobin 2001–2003: No Emergence of Resistant Strains and No Mutations at Codon 143 or 129 of the Cytochrome b Gene

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The sensitivity of Magnaporthe grisea to Metominostrobin (ORIBRIGHT^®, a QoI fungicide) was examined. Six isolates collected in 1999, prior to the introduction of metominostrobin, were tested by conducting in vivo assays to establish a baseline for the sensitivity of the fungus. The mean value of the EC₅₀ (ranging from 0.65 to 11.8 μg/ml) was 3.3 μg/ml. Ninety isolates were collected in 2001–2003 and 56 isolates were subjected to in vivo assays. EC₅₀ values ranged from less than 0.1 to 9.4 μg/ml and no significant difference to the baseline was observed. A point mutation at nucleotide position +428 or +387 in the cytochrome b gene, resulting in the replacement of glycine 143 with alanine (G143A) or of phenylalanine 129 with leucine (F129L) at the amino acid position of cytochrome b known to be the cause of resistance to QoI, was not observed in any of the 96 field isolates including the six collected in 1999. © Pesticide Science Society of Japan