Mycosphaerella horii

This pathogen features a complex life cycle, existing as Mycosphaerella horii in its sexual (teleomorph) stage and as Cercospora kaki in its asexual (anamorph) stage. Both forms are crucial for the fungus's survival and propagation.

As an obligate parasite, it relies on host tissues to complete its life cycle. It is classified under the order Capnodiales, adapting well to the specific environmental conditions of persimmon growing regions.

The fungus is microscopic, making direct visual identification of the pathogen difficult without specialized laboratory equipment. Identification in the field is usually based on the characteristic symptoms it produces on leaves.

Its survival strategy involves staying dormant in infected debris, ensuring the fungus remains present in the orchard from one growing season to the next if sanitary measures are ignored.

The primary host for Mycosphaerella horii is the Oriental persimmon. The fungus targets the leaves, which are essential for the plant's metabolic functions, including photosynthesis.

Severe infections lead to significant physiological stress for the tree. As leaves become necrotic and fall prematurely, the tree's ability to store energy for the next growing season is severely compromised.

The reduction in the functional leaf area negatively impacts fruit development, leading to smaller, less sweet fruit and a decrease in overall marketable yield.

Prolonged defoliation weakens the tree's immune system, making it more susceptible to frost damage during winter months and secondary infections by other opportunistic pathogens.

In mature orchards, an unchecked infestation can reduce the overall vigor of the trees, leading to long-term decline in productivity and potential loss of entire branches.

The disease cycle begins in early spring, when ascospores are released from the infected leaves on the ground. These spores are spread by wind and rain onto the emerging foliage.

The fungus is most active during the summer months, especially when periods of high humidity and rainfall occur. These conditions are ideal for the rapid development of the asexual stage (Cercospora kaki).

As the season progresses, secondary cycles of infection occur throughout the summer, significantly increasing the number of lesions on the leaves of the persimmon trees.

The disease reaches its peak severity in late summer and early autumn. During this time, heavy infestations often lead to premature leaf drop, which can happen several weeks before the normal dormancy period.

Once the leaves fall to the ground, the fungus develops its overwintering structures (pseudothecia), where it remains dormant through the winter, ready to start the cycle again the following spring.

Symptoms typically start as small, angular to circular spots on the upper surface of the leaves. These spots are initially brownish and are often overlooked in the early stages.

As the infection progresses, the lesions expand, developing a gray or light-brown center surrounded by a distinct dark-brown or black border, a hallmark sign of this pathology.

• Development of small brownish spots on leaves.
• Enlargement of spots and formation of necrotic tissues.
• Appearance of black fruiting bodies (pycnidia) on the underside of the leaves.
• Chlorosis (yellowing) of the leaf tissue surrounding the necrotic spots.
• Massive leaf shed before the natural autumn senescence.

In advanced cases, multiple spots may coalesce, covering large portions of the leaf blade, which leads to total leaf death and early abscission.

The most important control measure is orchard sanitation. Removing and destroying fallen leaves during late autumn is critical to eliminate the primary source of the fungus for the next year.

Proper pruning practices are essential to maintain an open canopy. Good airflow and sunlight penetration reduce leaf wetness, creating a microclimate that is less favorable for fungal growth.

Copper-based fungicide applications during the dormant season (late winter or very early spring) help to eradicate the pathogen's resting structures before they release spores.

During the growing season, if the disease is detected, the application of systemic or contact fungicides, according to local regulatory guidelines, is necessary to protect the foliage.

Maintaining tree vigor through proper fertilization and irrigation helps the persimmon trees withstand the pressure of the pathogen and minimizes the negative impact on fruit quality.