A method for monitoring the sensitivity of Botrytis cinerea to pyribencarb

Pyribencarb is a novel benzylcarbamate-type fungicide having excellent activity against a wide range of plant pathogenic fungi, especially gray mold diseases caused by Botrytis cinerea. The primary target site of pyribencarb is the Qo site of cytochrome b in the electron transfer system of the respiratory chain. The inhibitory effects of pyribencarb to cytochrome b enzyme on the transfer system of a QoI-resistant strain of B. cinerea are stronger than those of other QoI fungicides. Pyribencarb exhibited adequate control in greenhouse trials when QoI-resistant strains were inoculated. We have developed a practical method for evaluating the sensitivity of B. cinerea to pyribencarb. The final concentrations of pyribencarb in the PDA medium were set at 1 and 100mg a.i. per liter with 1mM salicylhydroxamic acid (SHAM). The isolates that were completely inhibited at 1mg a.i. per liter of pyribencarb were “sensitive strains,” and the isolates that were inhibited by more than 80% at 100mg a.i. per liter of pyribencarb were “weakly resistant strains.” In our assays so far, no strains with mycelial growth inhibition rates of less than 80% at 100mg per liter of pyribencarb have ever been found. In the event that such strains should be found in the future, it will be necessary to monitor their sensitivity to pyribencarb using an in vivo assay.