Allophomosis

The symptoms of allophomosis manifest as necrotic spots, typically localized on stems, leaves, and petioles. These spots vary in shape, ranging from circular to elongated necrotic lesions.

Over time, the affected tissues turn brown or dark gray. A characteristic diagnostic feature is the appearance of tiny black dots — the pycnidia of the fungus, concentrated in the center of the lesions.

Under high humidity, a fungal bloom consisting of conidia mass may appear on the affected areas. Severe stem infections often lead to deformation, disrupting the plant's physiological transport processes.

In some crops, allophomosis causes premature leaf wilting, starting from the lower levels. If the infection penetrates deep into the stem, it may lead to crop lodging during late growth stages.

Infection of the root system or root collar causes tissue decay, eventually leading to the death of the entire plant. Accurate diagnosis requires a thorough inspection of all plant organs.

The causative agent of the disease is the fungus Allophoma labilis, which belongs to the class of Ascomycetes. Previously, this pathogen was often classified within the genus Phoma, reflecting its biological similarity to other phoma-like infections.

This microscopic fungus infects plant tissues by forming pycnidia — specialized fruiting bodies that produce conidia. These spores are the primary source of infection and ensure the spread of the disease throughout the growing season.

The pathogen can survive in soil and on plant debris for extended periods, utilizing them as a nutrient substrate. The fungus possesses high adaptability, allowing it to thrive under various environmental conditions.

The infection spreads through contact with infected seeds, agricultural tools, or by wind-dispersed spores. The fungal mycelium penetrates the host tissues, progressively breaking down cell walls.

A specific characteristic of this pathogen is its potential for latent development, where external signs of the disease become visible only when the plant's immunity is weakened or favorable environmental factors occur.

High air humidity and moderately warm weather are most favorable for the development of Allophoma labilis. The optimal temperature range for spore germination and active mycelial growth is between +18...+24 degrees Celsius.

Frequent rainfall, fog, and heavy dew create an ideal microclimate for the dispersal of conidia across the field. Densely sown crops with poor air circulation are significantly more susceptible to infection.

Failure to follow agronomic standards, such as excessive nitrogen fertilization, reduces the natural resistance of plants. Weakened crops, especially those damaged by pests, are infected first.

The infection background increases significantly when crop rotation is neglected, allowing the host crop to return to the same field too early. Plant debris remaining in the soil acts as a reservoir for the pathogen.

Mechanical tissue damage or traces of insect activity provide entry points for the infection, allowing the fungus to penetrate plant tissues without hindrance.

The primary damage caused by allophomosis is a significant reduction in yield and a deterioration in product quality. Affected plants appear stunted and exhibit low growth energy.

In cases of massive infestation, a large portion of the harvest can be lost. The fungus destroys tissues, blocking the transport of water and nutrients from the roots to the vegetative organs.

Seed infection leads to a loss of germination and vitality. This causes issues with crop density and necessitates additional costs for reseeding the affected areas.

Economic losses are compounded by the costs of fungicide applications, the loss of commercial product value, and the need for field sanitation after harvest.

The infection also depletes the plant, making it more vulnerable to secondary pathogens, which greatly complicates the overall crop protection and treatment strategy.

Effective control of allophomosis is based on strict adherence to crop rotation with a 3–4 year break. This interrupts the fungal life cycle in the soil and reduces the overall inoculum level.

An important step is the use of high-quality, certified seed material. Seed treatment with systemic fungicides allows for the elimination of the pathogen at the sowing stage.

Agronomic measures include deep plowing for the thorough incorporation of plant debris, which serves as a disease reservoir. Rigorous weed control also reduces the potential for fungal propagation.

• Application of preventative fungicide sprays.
• Optimization of crop density to ensure ventilation.
• Balanced mineral nutrition (phosphorus and potassium enhance immunity).
• Prompt control of pests that damage plant tissues.

During the active growing season, if the first signs of the disease appear, it is necessary to spray with authorized systemic fungicides effective against phoma-like fungi.