Studies in the control of Botrytis cinerea pers ex. Fr. on strawberries

A review of the literature concerning Botrytis cinerea as a cause of post-harvest spoilage of strawberries, and the methods used in prolonging shelf life has been made. Also included in the review was the mode of action of fungicides used to inhibit decay. The results of disease assessments of Botrytis rot on strawberries in the field at Lincoln College, Canterbury, New Zealand, showed that the intensity of rotting of the cultivar Redgauntlet was higher in December than in January or March. Although Botrytis rot was the most important disease in December and January, the incidence of Rhizopus rot in the field was very low. The difference between the incidence of Botrytis rotting of berries of cultivar Tioga when overhead irrigated and trick1e irrigated was not significant. The effect of five fungicides; benomyl, thiabendazole (TBZ), dicloran, dichlofluanid (DCF) and thiram on growth and germination of strains of B. cinerea isolated from strawberries (X and St), grapes (G) , tomatoes (T) and lettuce (L) was studied in vitro. Concentrations of 0.001 mg/ml AI benomyl; 0.012 mg/ml AI TBZ; 0.05 mg/ml AI dicloran and 0.10 mg/ml AI DCF brought about total inhibition of growth of B. cinerea. Up to 1.6mg/ml AI thiram was used to inhibit growth of B. cinerea but total inhibition was not obtained for the isolates tested, except for isolate L. Conidia of B. cinerea were found to germinate in the presence of benomyl (0.10 mg/ml AI) and TBZ (0.12 mg/ml AI) to produce swollen; and distorted germ tubes which branched more frequently than normal. Dicloran (0.10 mg/ml AI), DCF (0.10 mg/ml AI) and thiram (0.16 mg/ml AI) inhibited germination of B. cinerea. Spore lysis was observed in some of the spores treated with dicloran. Dicloran (0.10 mg/ml AI) and thiram (0.16 mg/ml AI) did not have a fungicidal effect on myceliun or spores of B. cinerea, thus the spores and mycelium regained their growth potential after subculturing onto fresh media. The five isolates of B. cinerea X, St, G, T and L differed in response and tolerance to the fungicides tested. Isolate L was significantly different from the others in cultural characters and was least susceptible to all the fungicides tested except for thiram to which it was the most susceptible. The five fungicides were also tested for their effectiveness in reducing storage rot. The fungicides were sprayed on cultivar Redgauntlet strawberry fruits and inoculated with spore suspension of B. cinerea. During storage, benomyl, TBZ and DCF treatment on strawberries decreased rotting caused by B. cinerea slightly more than dicloran and thiram when stored for 7 days at 15° and 24°. The effect of relative humidity was dependent on the temperature of incubation and the length of storage period. Benomyl was effective in controlling decay at 75% r.h., 67% r.h. and 85% r.h. stored at 15° for five days, but not at 24°. However, when stored further for 10 days the percentage decay was higher at 15° than at 24°. The major contaminants of strawberries in storage were B. cinerea, Rhizopus sp. and superficial growth of Cladosporium sp., although organisms like Aspergillus sp., Penicillium sp. and Altenaria sp. were isolated from the surface of harvested berries before storage. In conclusion, Botrytis rot caused by B. cinerea was not controlled effectively by fungicide treatments but fungicides, especially in conjunction with other treatments, gave some delay of decay.