Anthracnose caused by Colletotrichum watphraense

The primary symptom of infection is the appearance of small, circular or irregular spots on leaves, shoots, and fruits. Over time, these spots enlarge, turn dark brown or black, and may feature a lighter center surrounded by a dark margin.

Acervuli of the pathogen, appearing as tiny black dots, develop on the affected tissues and become particularly visible under high humidity conditions. During periods of high rainfall, a pink or salmon-colored mass of conidia may emerge on the surface of the lesions.

Fruit infection leads to deformation, the development of deep ulcers, and subsequent rotting. The disease often affects leaf petioles and stems, causing premature wilting and the death of vegetative plant organs.

Young plants may exhibit wilting symptoms caused by the disruption of conductive tissues due to necrotic stem lesions. In some cases, the disease manifests as a "burn," where individual necrotic spots merge into large areas of dead tissue.

A key characteristic of this species is its ability to infect a wide range of crops, including fruits, vegetables, and ornamental plants, making it a significant threat to various agricultural ecosystems.

The causal agent of the disease is the microscopic fungus Colletotrichum watphraense, belonging to the division Ascomycota. This pathogen is part of the Colletotrichum gloeosporioides species complex, known for its high aggressiveness.

The fungus reproduces asexually via conidia produced in acervuli. These conidia are disseminated by air currents, rain splashes, or during field operations.

The fungal mycelium can persist for long periods in plant debris, soil, and seeds. The pathogen invades plant tissues through both natural openings, such as stomata, and directly through the cuticle using specialized infection structures called appressoria.

The high genetic variability of this species allows it to adapt rapidly to different environmental conditions and overcome the resistance barriers of many commercial varieties. Molecular diagnostics is currently the only reliable method for identifying this specific species.

During its lifecycle, the fungus secretes specific enzymes and toxins that degrade host cell walls, facilitating the colonization of plant tissues.

The development of anthracnose caused by Colletotrichum watphraense is directly dependent on humidity levels and ambient temperatures. Optimal conditions for spore germination are relative humidity above 85% and temperatures in the 22–28°C range.

Prolonged rainy periods, fog, and heavy dew create an ideal environment for infecting new plant parts. Rain splashes serve as the primary mechanism for distributing conidia from infection sources to healthy tissues.

High planting density, poor ventilation in greenhouses, and improper agricultural practices significantly accelerate the spread of the epidemic. Lack of airflow maintains a microclimate with high humidity even during dry periods.

Weakened plants suffering from nutrient deficiencies or stress due to adverse weather conditions are infected much faster. Mechanical damage to the skin of fruits and leaves further facilitates the penetration of the pathogen.

The accumulation of inoculum is facilitated by the presence of uncollected plant debris, which acts as a reservoir for the fungus during off-seasons.

The harmfulness of the disease lies in significant losses of fruit marketability and overall crop yield. Severely infected fruits become unsaleable and rot quickly, making them unsuitable for storage.

Damage to the leaf canopy reduces photosynthetic activity, which leads to overall plant weakening, poor floral bud development, and lower crop quality.

In cases of severe anthracnose outbreaks, yield losses can range from 30% to 80%, depending on the crop and weather conditions. The disease poses a particular threat in nurseries and greenhouses, where infections spread rapidly.

Stem infection can lead to plant lodging, making crops more vulnerable to secondary pathogens and pests. On a global scale, this fungus is a threat to international trade due to strict quarantine regulations.

Beyond direct economic losses, the costs associated with disease management, including fungicide applications, significantly increase the cost of production.

The protection strategy includes a combination of agronomic and chemical measures. The most crucial step is using healthy, certified seeds and planting material that has been treated with fungicides.

Preventive measures include the removal and destruction of crop residues after harvest, as well as strict crop rotation practices to prevent the accumulation of inoculum in the soil.

To prevent disease spread, it is necessary to conduct timely sanitary pruning of infected plant parts and maintain optimal planting density to ensure proper aeration.

• Application of contact and systemic fungicides based on copper, strobilurins, or triazoles.
• Regular monitoring of field conditions during high-humidity periods.
• Ensuring balanced mineral nutrition to strengthen plant immunity.

When selecting fungicides, it is recommended to rotate active ingredients with different modes of action to prevent the development of pathogen resistance.