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In Vitro Assessment of Penicillium expansum Sensitivity to Difenoconazole
Mohammed Khadiri1,2, Hassan Boubaker2, Abdelaaziz Farhaoui1,3
1Phytopathology Unit, Department of Plant Protection, Ecole Nationale d'Agriculture de Meknès, Km10, Rte Haj Kaddour, BP S/40, Meknes 50001, Morocco.
Abstract:
Penicillium expansum causes blue mold, a major post-harvest disease affecting apples. This disease is commonly managed using fungicides, including Difenoconazole (Dif), a demethylation inhibitor (DMI) approved for its control. This investigation aims to evaluate the baseline sensitivity of 100 P. expansum isolates to Difenoconazole. The isolates were collected from symptomatic apples in 34 storage warehouses across the Fes-Meknes and Draa-Tafilalet regions over three years (2020, 2021, and 2022). The study revealed an increase in the percentage of inhibition of mycelial growth and spore germination of P. expansum proportional to the increasing concentration of the fungicide. Moreover, the results indicate that 46 isolates were able to develop even at a concentration of 5 µg/mL of Dif (the suggested discriminatory dose), indicating reduced sensitivity to this fungicide. The analysis of the values of the effective concentration to inhibit 50% (EC50) of mycelial growth of P. expansum ranging from 0.027 to 1.673 µg/mL (mean: 0.263 µg/mL, variation factor: 62.507) and for spore germination from 0.0002 to 0.787 µg/mL (mean: 0.048 µg/mL, variation factor: 4113.835). The wide variation in EC50 values indicates significant variability in the isolates' responses to Dif, likely due to diverse sampling in space and time. Our results showed that some P. expansum isolates could grow even at high concentrations of Dif, indicating limited efficacy of this treatment. The EC50 of five isolates exceeded 0.92 µg/mL, suggesting potential resistance. This study indicates reduced sensitivity and possible emergence of resistant strains. Notably, it is the first evaluation of P. expansum sensitivity to Dif in Morocco.
Insights
Blue mold in apples, caused by Penicillium expansum, shows reduced sensitivity to the fungicide Difenoconazole (Dif). Some isolates grew even at high concentrations, indicating potential resistance and limited treatment efficacy.
Area of Science:
- Plant Pathology
- Mycology
- Agricultural Science
Background:
- Penicillium expansum causes blue mold, a significant post-harvest apple disease.
- Difenoconazole (Dif), a demethylation inhibitor (DMI) fungicide, is widely used for its control.
Purpose of the Study:
- To evaluate the baseline sensitivity of Penicillium expansum isolates to Difenoconazole.
- To assess the potential emergence of Difenoconazole-resistant strains in Morocco.
Main Methods:
- Collected 100 P. expansum isolates from symptomatic apples across 34 warehouses over three years (2020-2022).
- Determined the effective concentration (EC50) for mycelial growth inhibition and spore germination inhibition.
- Assessed isolate development at a discriminatory dose of 5 µg/mL of Difenoconazole.
Main Results:
- 46 out of 100 isolates showed reduced sensitivity, growing at 5 µg/mL of Dif.
- EC50 values for mycelial growth ranged from 0.027 to 1.673 µg/mL (mean 0.263 µg/mL).
- EC50 values for spore germination ranged from 0.0002 to 0.787 µg/mL (mean 0.048 µg/mL).
- Five isolates exhibited EC50 values exceeding 0.92 µg/mL, indicating potential resistance.
Conclusions:
- Significant variability in Difenoconazole sensitivity among P. expansum isolates was observed.
- Reduced sensitivity and the potential emergence of Difenoconazole-resistant strains are indicated.
- This is the first study evaluating P. expansum sensitivity to Difenoconazole in Morocco.
