Graphostroma platystomum

The fungus develops stromata beneath the bark, which serve as its reproductive and defensive structures. These structures protect the mycelium from environmental fluctuations while allowing spore dispersal.

By invading the cambial layer, the pathogen disrupts the vascular system, preventing the tree from effectively transporting water and nutrients, which eventually leads to localized tissue death.

The biological cycle of the fungus is strictly adapted to the host, taking advantage of the bark's chemical composition to sustain long-term growth and mycelial expansion within the tree trunk.

Morphologically, the fungus is characterized by the formation of small, flat, black stromata that break through the epidermis, which is a diagnostic feature used in identification.

The primary symptom of this disease is the development of necrotic areas on the bark. These lesions usually appear as discolored patches that expand over time as the fungus matures.

As the infection progresses, small, dark fungal fruiting bodies emerge through cracks in the bark. This indicates that the pathogen has successfully colonized the interior tissues.

Bark splitting and peeling are common occurrences in infected areas. The separation of the bark from the woody trunk creates cavities where secondary pathogens can settle and cause further decay.

Foliage symptoms include premature yellowing and leaf drop. This occurs because the fungal colonization of the cambium cuts off the supply of essential resources to the branches and canopy.

• Discolored necrotic lesions on the trunk.
• Emergence of black stromata through the bark.
• Bark cracking and detachment from the wood.
• Premature canopy thinning and leaf yellowing.
• Branch dieback in the upper crown.

The proliferation of Graphostroma platystomum is highly dependent on humidity levels. High atmospheric moisture and poor aeration within the tree canopy favor spore germination and colonization.

Weakened trees, especially those suffering from drought stress or previous environmental injuries, provide the perfect substrate for the fungus to establish its infection.

Temperatures ranging from 15°C to 25°C are optimal for fungal growth. During these periods, the pathogen spreads most aggressively, utilizing moisture to facilitate its reproductive cycle.

Mechanical injuries, such as those caused by storms, pruning, or human activity, act as primary entry points for the spores. Wounds allow the fungus to bypass the tree's natural bark defenses.

Spore dissemination occurs primarily via wind and rainwater splash, but insects residing on the bark can also serve as vectors, transporting the pathogen between trees.

The main threat posed by this fungus is the gradual death of the cambium, which leads to structural weakening of the trunk. This can compromise the tree's overall stability and longevity.

In urban landscapes, infected trees lose their aesthetic value quickly, leading to the necessity of removal. This disrupts the urban canopy cover and reduces the ecosystem services provided by trees.

By creating open wounds and inducing systemic stress, the fungus makes trees significantly more susceptible to secondary attacks by wood-boring insects, accelerating the rate of tree decline.

The structural degradation of the wood can become a safety hazard in public areas, as branches or even the entire trunk may break under high wind conditions due to fungal rot.

Economic impact is significant due to the costs associated with tree removal, maintenance of affected stands, and the loss of mature, high-value landscape trees that are difficult to replace.

Sanitation is the most effective management strategy. This involves the removal of dead or infected branches and the scraping of localized necrotic bark to reach healthy, clean wood.

All pruning wounds should be treated with appropriate fungicides or wound-healing sealants to prevent spore ingress, ensuring the tree has time to heal its natural defenses.

Enhancing the overall tree vigor through consistent irrigation and fertilization helps the host tree mount a better defense against fungal colonization.

Preventive fungicide spraying may be necessary in areas where the disease is known to be prevalent, especially during the active growing season when spores are most active.

Proper disposal of all pruned materials, including the burning of diseased bark, is essential to limit the inoculum load in the area and prevent the spread of the pathogen to neighboring trees.