Powdery mildew of cyclamen

Pathogen and disease type
The disease is caused by the fungus Oidium cyclaminis, a typical obligate biotroph belonging to the powdery mildew group. The fungus colonizes the surface of the plant tissue, forming a dense white mycelium network. It extracts nutrients from the host cells using haustoria, which penetrate the plant epidermis without causing immediate necrosis, though it severely impacts plant physiology.

Host plants
The primary host for this pathogen is the cyclamen (Cyclamen persicum). It is a highly specialized fungus that thrives in environments where cyclamens are cultivated in large quantities. It is particularly problematic in greenhouses and indoor domestic settings where environmental parameters are kept stable for plant growth but also favor fungal sporulation.

Symptoms and signs
The disease is characterized by the appearance of white, powdery, fungal patches on the upper and lower surfaces of the leaves, as well as on flower stalks. These patches consist of mycelium and conidial chains. In later stages, affected leaves become distorted, brittle, and may turn yellow or brown. Flowers may fail to open or become discolored and deformed.

Conditions for development
Oidium cyclaminis thrives in moderate temperatures ranging from 18°C to 24°C combined with high relative humidity. Poor airflow and stagnant air within the plant canopy create the perfect microclimate for the rapid germination of conidia. Spread is facilitated by air currents, splashing water during irrigation, and handling of infected plant material.

Damage and control measures
The economic impact of this disease is significant, as it renders the plants unmarketable and reduces their lifespan. Effective management strategies include:

• Ensuring adequate spacing between pots to improve air circulation.
• Managing greenhouse humidity through consistent ventilation.
• Avoiding excessive nitrogen fertilization which leads to overly succulent growth.
• Applying systemic fungicides, such as those containing triazoles or strobilurins, at the first signs of symptoms.
• Sanitation measures, including the removal and disposal of infected leaves to prevent further spread.