MYCELIAL SENSITIVITY ASSAY OF POSTHARVEST GREY MOULD FROM 'FORELLE' PEARS TO ANILINOPYRIMIDINE FUNGICIDE PYRIMETHANIL

In South Africa, significant postharvest losses occur in the ‘Forelle’ pear cultivar due to secondary infections caused by grey mould pathogen Botrytis cinerea. Before storage, fruit are drenched or dipped with fungicide to reduce the occurrence of secondary infections. However, the sensitivity levels of B. cinerea towards fungicides registered for postharvest use is not known in South Africa and needs to be investigated for better decay management strategies. In this study, the mycelial sensitivity of 122 unexposed B. cinerea isolates from stored ‘Forelle’ pears towards registered anilinopyrimidine fungicide pyrimethanil was examined. A sub-group consisting of 34 isolates was used to establish baseline sensitivity and the EC₅₀-values ranged from 0.078 to 0.127 mg L^-1 with a mean value of 0.096 mg L^-1. A discriminatory dose of 3.20 mg L^-1 was used to screen the whole population and a high frequency of pyrimethanil-sensitive isolates (87.7%) were found. Remaining isolates were considered to be less sensitive.