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

The sensitivity of Magnaporthe grisea to Metominostrobin (ORIBRIGHT (R) 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 mu g/ml) was 3.3 mu g/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 mu g/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. (c) Pesticide Science Society of Japan.