Vietnamese anthracnose

A typical symptom is the appearance of local, sunken spots on leaves, fruits, and stems, which may be circular or irregular in shape. Affected areas often have a dark color, sometimes with a lighter center.

Under conditions of high humidity, characteristic fungal fruiting bodies, known as acervuli, form on the surface of the lesions. These look like small cushions where conidial masses, often pink or orange, are produced.

As the disease progresses, the lesions may coalesce, covering significant areas of the leaf surface. This results in premature wilting and subsequent shedding of the affected leaves.

On stems, the infection manifests as longitudinal cracks or ulcers, which can obstruct the transport of water and nutrients to the upper parts of the plant.

When fruits are affected, rot develops, rendering them unsuitable for storage or transport. In highly humid conditions, the fruits become covered with a layer of spores, rapidly losing their marketability.

The causal agent of the disease is the fungus Colletotrichum vietnamense, which belongs to the class Ascomycetes. This phytopathogenic microorganism is capable of living parasitically on various parts of host plants.

This pathogen is a highly specialized species of the genus Colletotrichum. Microscopic analysis confirms the presence of characteristic conidia and sclerotia, which ensure the survival of the fungus in adverse environmental conditions.

The fungus spreads primarily via conidia, which are dispersed by rain splashes, wind, or insect vectors. Primary infection usually occurs through mechanical tissue damage or natural openings such as stomata.

The biology of the pathogen is closely tied to the presence of plant debris in the soil, where it can persist for long periods. The high plasticity of its genome allows the fungus to adapt rapidly to new hosts.

The infection cycle includes conidial germination, the formation of appressoria for penetration of the cuticle, and subsequent mycelial development inside plant cells, eventually leading to tissue necrosis.

The disease develops most actively under high air humidity and moderately high temperatures. Rainy periods during the growing season are ideal for the mass spread of the disease.

The temperature range favoring mycelial development varies from +20 to +28 degrees Celsius. Prolonged wetting of the leaf surface, such as from dew or fog, significantly accelerates spore germination.

Poor agricultural practices, such as excessive planting density, hinder plant aeration. The lack of air circulation creates a localized microclimate with high humidity, which is highly conducive to infection.

Weakened plants, suffering from nutrient deficiencies or pest damage, are at increased risk of epiphytotic disease development.

Improper irrigation methods, especially overhead watering that wets the foliage, trigger the spread of spores from infected plants to healthy neighboring specimens.

The primary damage is a significant reduction in yield and a decline in product quality. Necrotic processes disrupt photosynthesis, leading to the overall weakening of the plant organism.

Infection of reproductive organs leads to significant losses of fruit during both the formation and ripening stages. This is particularly critical for commercial crops.

Infected plants serve as a source of inoculum for neighboring fields, creating a risk of total crop failure in favorable climatic conditions. The pathogen can survive in seeds and crop residues.

Additional costs are associated with the implementation of control measures. The use of pesticides increases production costs and requires strict adherence to pre-harvest intervals.

In the absence of control, the disease can lead to the total loss of certain crops, especially in regions with tropical or subtropical climates where the pathogen is most active.

The control strategy includes the use of healthy seeds and planting material that has been disinfected beforehand. Crop rotation is a fundamental method for reducing the inoculum load in the soil.

An essential practice is the timely removal and destruction of crop residues, which serve as a reservoir for the fungus. Regular weeding helps prevent the accumulation of the pathogen.

• Application of copper-based fungicides or synthetic systemic agents.
• Ensuring optimal planting density to improve air circulation.
• Implementation of rational drip irrigation to avoid wetting the aerial parts of the plant.
• Utilization of resistant cultivars and hybrids if available in the registry.

When the first signs of the disease are detected, sanitary pruning of the affected parts is necessary. Tools used for pruning must be disinfected after use.

Preventive treatments with biological fungicides during periods conducive to pathogen spread can significantly reduce the intensity of the infectious background.