Curvularia eragrostidis

The fungus produces septate, dark-pigmented mycelium and conidiophores with characteristic multicellular conidia. The conidia have a curved shape, which gave the genus its name (Curvularia). The median cells of the spores are typically darker than the terminal ones.

Systematically, this species belongs to anamorphic fungi. Its teleomorph stage (sexual) is known as Cochliobolus eragrostidis, although the conidial sporulation plays the key role in field epiphytotics.

The fungus is a facultative parasite capable of surviving in the soil and on plant debris in the form of mycelium and chlamydospores. This allows the pathogen to survive adverse conditions and quickly resume activity when warmer weather arrives.

The dispersal of conidia occurs primarily through wind, rain splashes, and during mechanical field operations. Its high adaptability allows it to infect both cultivated crops and wild grasses.

The pathogen affects a wide range of hosts, including cereals, forage grasses, and some species of ornamental and fruit crops. It causes the most significant economic losses in maize, rice, and turfgrass crops.

In maize, the fungus causes leaf spot development, which, under severe infection, leads to premature drying of the leaf blade. A reduction in photosynthetic area results in lower grain yield.

In various grass species, Curvularia eragrostidis triggers the development of root and basal rots. This disrupts the plant's vascular tissues, often leading to lodging and reduced productivity of the crop.

Infection of inflorescences and seeds is a serious problem, as the fungus is seed-borne. Infected seeds have low germination rates and often serve as a primary source of infection for young seedlings.

In ornamental nurseries, the fungus can cause damage to young shoots and leaves, which significantly reduces the aesthetic value of the plants and may lead to seedling death under high humidity conditions.

Active development of the pathogen is observed under conditions of high humidity and warm temperatures. Optimal parameters for conidia germination and tissue infection range from +25°C to +30°C.

Primary infections often occur in the spring when warm and humid weather is established after sowing. During this period, crop residues and infected seeds serve as the primary source of inoculum.

Throughout the growing season, the fungus produces several generations of conidia, which facilitates the rapid spread of the disease during periods of frequent rainfall or dew. Relative humidity above 80% is a critical risk factor.

During dry periods, disease development slows down, but the fungus remains viable in plant tissues in a latent form. When weather conditions change toward higher moisture, the disease manifests with renewed vigor.

Toward the end of the season, as temperatures drop, the pathogen enters a dormant state, forming chlamydospores or surviving within plant debris, preparing for overwintering in the soil substrate.

The primary symptom of infection is the appearance of leaf spots, which range in color from brown to nearly black. These spots often have a light-colored central zone and a distinct chlorotic halo around the periphery.

Under high humidity, an olive-black or grey velvety mold forms on the surface of the spots, consisting of the fungus's conidiophores and spores. This mold serves as a diagnostic sign for microscopic analysis.

Dark longitudinal streaks or ulcers may develop on the stems of infected plants. In the affected areas, the tissues soften, which subsequently leads to stem breakage during strong winds.

Root rot manifests as yellowing of the lower leaves, gradual wilting, and overall stunted growth of the plant. The roots turn brown or black and become fragile.

• Appearance of necrotic spots of irregular shape.
• Development of dark sporulation mold.
• Stunted growth and wilting.
• Darkening and rotting of the basal zone.

Agrotechnical practices remain the foundation of control: strict crop rotation excluding susceptible species, thorough incorporation of plant debris, and the elimination of weed reservoirs.

The use of healthy, certified seed material is critical. Seed treatment with broad-spectrum fungicides helps to reduce the level of primary infection.

If signs of an outbreak are detected in the field, spraying with fungicides from the triazole and strobilurin groups is recommended. Treatments should be applied prophylactically or at the first sign of symptoms.

It is important to manage plant density, as excessive crowding promotes a microclimate with high humidity, which is favorable for fungal development.

Breeding and the use of resistant hybrids or varieties remain the most effective long-term solution, allowing for the minimization of costs associated with chemical crop protection.