Colletotrichum dematium

Colletotrichum dematium is a fungal pathogen belonging to the kingdom Fungi, phylum Ascomycota, and the genus Colletotrichum. It is a widely distributed pathogen responsible for anthracnose diseases.

The fungus develops within plant tissues, forming characteristic fruiting bodies called acervuli. These appear as small, dark, cushion-like structures that produce conidia, which are then spread by rain splashes and wind.

Identification in the laboratory is performed via microscopic analysis. Conidia exhibit a distinct sickle or spindle shape, and the presence of setae within the acervuli is a key diagnostic feature for this species.

This species is considered polymorphic and infects a broad range of dicotyledonous plants. Its survival is ensured by the ability to persist in crop residues as mycelium and sclerotia.

The fungal life cycle involves an asexual stage, which is the dominant factor in the mass infection of crops during the growing season.

This pathogen affects a vast number of agricultural and ornamental crops. Species at risk include legumes (soybeans, beans), solanaceous crops, onions, and various industrial and oilseed crops.

The fungus causes necrosis on various plant organs, including stems, leaves, petioles, pods, and seeds. The pathogen is particularly devastating when it develops during the crop yield formation phase.

The damage manifests as a drastic reduction in the photosynthetic activity of leaves due to necrotic lesions. This leads to premature wilting and abscission of the foliage.

When legumes are infected, the fungus penetrates the pods, resulting in shriveled seeds and loss of seed quality. Infected seeds often serve as the primary source of inoculum for the next season.

Severe infection can cause systemic chlorosis and the total death of young plants, significantly reducing plant stand density and causing substantial yield losses.

Active infection starts under warm and humid weather conditions. Optimal temperatures for spore germination range from +20 to +28 degrees Celsius with high relative humidity.

During summer, especially after heavy rainfall, there is a peak in fungal sporulation. Rain splashes facilitate the dispersal of conidia onto healthy parts of neighboring plants.

The pathogen can remain viable in soil and plant debris for several years. Primary infection of crops often occurs in spring upon contact of seedlings with contaminated residues from the previous harvest.

Disease progression is accelerated by periods of prolonged fog and dew, which create a favorable wet environment on the surface of leaves for the germination of infectious hyphae.

By autumn, the fungus forms denser structures that allow it to overwinter in adverse conditions, preparing the foundation for infecting the next generation of crops.

Early symptoms include small brown or dark spots on leaves that gradually enlarge. A darker border is often visible around the edges of these spots.

The central part of the lesion eventually lightens, becoming grayish or whitish. In these areas, small black dots — the acervuli — become visible to the naked eye or through a magnifying glass.

Stem infections manifest as longitudinal dark streaks or sunken lesions. In the affected areas, tissues may crack, facilitating secondary infection by other microorganisms.

In some crops, the disease appears as curling and deformation of leaves. Under high humidity, a faint mycelial growth may appear on the lesions, which is a classic sign of anthracnose.

Pod infection appears as sunken brown spots. In severe cases, the fungus penetrates the pod walls to reach the seeds, leaving dark spots or fungal growth, which decreases the commercial value of the produce.

• Using only certified, healthy seed material that has undergone phytosanitary inspection.
• Implementing crop rotation by excluding susceptible species for 3–4 years.
• Thorough incorporation and destruction of crop residues after harvest, where the pathogen survives.
• Application of systemic and contact fungicides during periods of high infection risk.
• Weed management to eliminate potential pathogen reservoirs in the field.

The choice of fungicides should be based on regulations for specific crops. Preventive treatments prior to the emergence of visible symptoms are the most effective strategy.