Leveillula

Leveillula is a genus of fungi responsible for a specific type of powdery mildew known as endophytic powdery mildew. Unlike most powdery mildew species that remain on the plant surface, the mycelium of Leveillula penetrates the plant tissue through the stomata, developing internally within the mesophyll layers.

This pathogen infects a wide range of economically important crops. Most notably, it affects solanaceous crops like tomatoes, peppers, and eggplants, as well as various onions, cucurbits, and legumes. Its ability to colonize host tissues internally makes it a persistent threat in both greenhouse and open-field environments.

Symptoms initially manifest as chlorotic spots on the upper side of the leaves, which gradually turn yellow and necrotic. Because the mycelium grows inside the leaf, the characteristic white powdery fungal growth is often sparse or found only on the underside of the leaves, frequently leading to misdiagnosis in early infection stages.

Environmental conditions favoring the development of Leveillula include temperatures ranging from 20°C to 30°C and alternating dry and humid periods. The spores are primarily wind-dispersed, and the pathogen thrives when humidity levels are moderate to high, allowing it to spread rapidly across entire plantations.

The economic impact of the disease is significant, as it leads to premature leaf senescence and defoliation. This reduction in photosynthetic area results in stunted growth, fruit malformation, and a drastic decrease in overall crop yield and quality, often requiring immediate intervention to prevent total crop loss.

Control strategies should be integrated to be effective. Key measures include:

• the use of resistant or tolerant cultivars;
• crop rotation practices to break the disease cycle;
• sanitation, including the removal and destruction of infected plant debris;
• the application of systemic fungicides, specifically those targeting internal mycelial development.