Cyttaria berteroi

Cyttaria berteroi is an obligate parasitic fungus belonging to the Cyttariaceae family, known for inducing the formation of large, woody galls on the trunks and branches of Southern Beech trees (Nothofagus species). This fungus acts as a significant biotic stressor in its native forest habitats, influencing tree architecture and longevity.

The disease is caused by the ascomycete Cyttaria berteroi. Upon infection, the pathogen stimulates abnormal growth in the host's plant tissues, leading to hypertrophy. These woody galls serve as the substrate for the fungus, where it develops its characteristic cup-shaped fruit bodies during the reproductive phase, often emerging from the gall surface in vibrant colors.

Symptoms of the infection typically manifest as irregular, tumor-like swellings on branches and stems. During the sporulation period, one can observe clustered, fleshy, or jelly-like fruiting bodies protruding from these galls. Eventually, severe infections result in the weakening of the branch structure, leading to structural failure or secondary wood decay.

The development and spread of Cyttaria berteroi are strongly influenced by high humidity and moderate temperatures. The spores are typically dispersed by wind, water splashes, and potentially by insect vectors that visit the fruit bodies. These conditions allow the fungus to effectively colonize susceptible hosts, particularly those that have existing bark injuries or are already under environmental stress.

The impact of this disease is characterized by a reduction in timber quality and potential branch loss, which can decrease the overall health of the forest stand. Management strategies are primarily focused on forest hygiene:

• Regular inspection of forest stands for signs of gall development.
• Removal and destruction of heavily infested trees.
• Promotion of tree vigor through silvicultural practices.
• Limiting mechanical damage to tree bark to prevent initial infection sites.