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Sensitivity of Podosphaera aphanis isolates to DMI fungicides: distribution and reduced cross-sensitivity
Audrey Sombardier1, Marie-Cécile Dufour, Dominique Blancard
1INRA, UMR Santé Végétale, Villenave d'Ornon, France.
Background:
Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management.
Results:
Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC(50) ranged from less than 0.1 to 14.67 mg L(-1) and for penconazole from 0.04 to 4.2 mg L(-1). A cross-analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides.
Conclusion:
The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control.
Insights
Strawberry powdery mildew in France shows reduced sensitivity to sterol demethylation inhibitors (DMIs) like myclobutanil and penconazole. This fungicide resistance necessitates updated pest management strategies to control the disease effectively.
Area of Science:
- Plant Pathology
- Agricultural Entomology
- Fungicide Resistance Studies
Background:
- Strawberry powdery mildew, caused by Podosphaera aphanis, management relies heavily on sterol demethylation inhibitors (DMIs).
- Reduced efficacy of DMIs, including myclobutanil and penconazole, has been reported by French strawberry growers.
- Investigating DMI sensitivity is crucial for effective disease control in strawberry cultivation.
Purpose of the Study:
- To assess the current sensitivity of French Podosphaera aphanis populations to DMIs.
- To identify the extent of reduced sensitivity to myclobutanil and penconazole.
- To provide data for optimizing pest management strategies against strawberry powdery mildew.
Main Methods:
- Leaf disc sporulation assays were employed to monitor fungicide sensitivity.
- Twenty-three isolates of Podosphaera aphanis from France were analyzed.
- Sensitivity to myclobutanil and penconazole was quantified using EC50 values.
Main Results:
- Significant variation in sensitivity to myclobutanil (EC50: <0.1 to 14.67 mg L⁻¹) and penconazole (EC50: 0.04 to 4.2 mg L⁻¹) was observed.
- A positive correlation between reduced sensitivity to myclobutanil and penconazole was identified.
- 73.9% of isolates showed reduced sensitivity to at least one DMI, with 47.8% less sensitive to both fungicides.
Conclusions:
- Sensitivity of strawberry powdery mildew in France to myclobutanil and penconazole has decreased.
- Urgent documentation of this reduced sensitivity is needed.
- Optimized control methods are required to manage fungicide-resistant strains effectively.
