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Penicillium expansum is the predominant fungal pathogen responsible for blue mold of apple. The sensitivity of three thiabendazole-sensitive (TBZS) and three thiabendazole-resistant (TBZR) isolates of P. expansum, collected from apple stores in Ontario, to fludioxonil was determined in vitro (conidial germination and colony diameter on fludioxonil amended medium) and in vivo (apples). On fungicide amended medium, the concentration of 50% inhibition (EC50) of germination for the TBZS and TBZR isolates of P. expansum ranged from 0.079 to 0.113 μg a.i. of fludioxonil/ml and for mycelial growth from 0.013 to 0.023 μg a.i. of fludioxonil/ml. Harvested apples were wounded and co-treated with a suspension of conidia of P. expansum and the fungicides by drenching. Fludioxonil at a concentration of 100 μg a.i./ml was found effective against blue mold induced by both TBZS and TBZR isolates of P. expansum on apple cv. Empire. In post-inoculation treatments, wounded apples were inoculated with P. expansum and incubated for 18–20 h at 13°C, and then drenched with appropriate concentrations of fungicides and incubated at 20°C for 6 days. Fludioxonil at a concentration of 100 μg a.i./ml controlled blue mold in the co-treatment and in the post-inoculation treatment on cvs. Empire and Gala. The activity of fludioxonil on two or more stages, conidial germination and mycelial growth, of life cycle of P. expansum and on decay formation in two cultivars of apples suggests that this compound potentially can provide an alternative to TBZ in post-harvest control of blue mold of apple, where any TBZR conidia are present. |
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