SENSITIVITY OF BOTRYTIS CINEREA FROM 'FORELLE' PEARS IN SOUTH AFRICA TO BENOMYL, IPRODIONE AND PYRIMETHANIL

‘Forelle’ pears are an important component of pome fruit exported from South Africa. However, postharvest grey mould caused by the pathogen Botrytis cinerea can be a significant problem in this cultivar, particularly as decay is often only detected once the pears reach the export markets. Fungicides applied at full bloom and postharvest are important in the integrated management of grey mould in pears, however, loss of fungicide sensitivity is common in B. cinerea. In this study, B. cinerea was isolated from long-term stored ‘Forelle’ pears from orchards in the Ceres production area of South Africa, showing calyx-end Botrytis. The baseline sensitivity of a sub-population (n=49) not previously exposed to botryticides was determined on a minimal medium amended with technical grade pyrimethanil. This population had a bimodal frequency distribution of pyrimethanil EC₅₀ values, which ranged from 0.06 to 0.36 mg L^-1, with a mean EC₅₀ value of 0.13 mg L^-1. The sensitivity of B. cinerea isolates (n=166) to benomyl, iprodione and pyrimethanil was tested using discriminatory concentrations of 3 and 5 mg L^-1 for each fungicide. None of the isolates grew on the pyrimethanil amended media, whereas one isolate grew on benomyl at 5 mg L^-1 (RF=0.6%), and two isolate grew on iprodione at 5 mg L^-1 (RF=1.2%). From this study we can conclude that the population tested is sensitive to the three fungicides, and these fungicides can be used to manage postharvest grey mould in the Ceres production area.