Microstromataceae

Microstromataceae is a family of fungi belonging to the order Microstromatales, characterized by their parasitic nature on various higher plants. These fungi typically target leaf tissues, twigs, and buds, causing specific types of lesions that can impact the overall health of woody species. Their development is intricately linked to the biological cycle of the host plant, often manifesting during moist conditions.

The pathogen spreads through the formation of microstromata—compact mycelial aggregates that erupt through the plant epidermis to release spores. Infection usually occurs through natural openings like stomata or via small wounds in the plant tissue. Once established, the fungus functions as a biotroph, absorbing nutrients from the host cells, which eventually leads to localized tissue death and structural weakness.

Host plants commonly affected by these fungi include diverse deciduous trees such as oak, hazel, and hornbeam. In agricultural and horticultural environments, these diseases can weaken young nursery stock or decrease the ornamental value of landscape trees. While rarely lethal to mature, healthy trees, repeated annual infections can lead to a significant decrease in vigor and photosynthetic capacity.

Symptomatology involves the appearance of chlorotic spots that transition into necrotic tissue. In many cases, a characteristic powdery or velvety coating appears on the underside of the leaves, indicating the active sporulation of the fungus. Key symptoms include:

• localized necrotic lesions;
• leaf deformation and curling;
• premature leaf drop during the growing season;
• reduced shoot development.

Effective management and disease prevention rely on cultural practices aimed at reducing inoculum pressure. This includes the removal and deep burial or burning of infected leaf litter, where the fungus overwinters. Improving canopy aeration through proper pruning is also essential to reduce humidity levels that favor fungal growth. In severe cases, preventive applications of fungicides can protect new growth during the critical early stages of the season.