Pleurophoma

Primary signs of infection appear as dark, most often brown or grayish spots on stems, petioles, and leaves of crops. The spots may have a distinct border or be irregular in shape.

Over time, small punctate fruiting bodies of the fungus, known as pycnidia, form in the infected areas. They look like tiny black bumps that can be seen with the naked eye or a magnifying glass on the surface of dead tissue.

As the disease progresses, plant tissues lose turgor and gradually wither. Stem infection is characterized by premature browning and cracking, which disrupts the normal sap flow within the plant.

A characteristic sign is focal distribution: symptoms are first found on individual specimens, after which the infection rapidly spreads to neighboring plants under favorable weather conditions.

In affected cereal or vegetable crops, basal zone necrosis can be observed, which often leads to stem lodging or total plant death during the grain filling or fruit formation stage.

The causative agent of the disease is a group of imperfect fungi from the genus Pleurophoma. These are pathogenic microorganisms belonging to the class Coelomycetes, characterized by the formation of pycnidia within the tissues of infected plants.

The fungus survives in infected plant debris, in the soil, and sometimes in seeds in the form of mycelium or specialized fruiting bodies. It can exist as a saprotroph for a long time, waiting for favorable conditions to switch to a parasitic lifestyle.

The life cycle of the pathogen is closely related to ambient humidity. The release of conidia from pycnidia occurs during wetting, after which spores are dispersed by raindrops, wind, or insects to healthy parts of the plants.

In phytopathological terms, Pleurophoma is often regarded as an agent causing stem necrosis and leaf spotting. The infection enters through natural openings (stomata) or mechanical damage to the epidermis.

Species identification of the pathogen requires laboratory analysis, as symptoms can be similar to other phomoid fungi such as Phoma or Phomopsis, which complicates field diagnosis.

The main factor contributing to the development of the infection is high relative humidity (above 85%). Prolonged periods of rainfall create an ideal environment for the germination of pathogen conidia.

The temperature optimum for the development of most Pleurophoma species is in the moderate range (+18°C to +25°C). Sharp fluctuations in daily temperatures combined with high humidity accelerate the epiphytotic development of the disease.

Poor agricultural practices, particularly high plant density, contribute to creating a microclimate with poor ventilation, which significantly increases the risk of rapid fungal spread within the agrocenosis.

The presence of free moisture (dew or rain) on leaves for several consecutive hours is a critical condition for the effective infection of plant tissues by fungal spores.

Weakened plants under stress from lack of nutrients, pest pressure, or herbicide damage become highly susceptible to the entry of this pathogen.

Pleurophoma leads to a significant reduction in yield due to the disruption of leaf photosynthetic activity and premature death of vegetative biomass necessary for high-quality harvest formation.

Fungal damage to stems reduces plant resistance to lodging, which makes high-quality mechanized harvesting impossible and leads to significant grain or fruit losses.

The quality of the harvested product also decreases: infected seeds often have low germination rates and can serve as a source of infection in the following growing season.

In vegetable crops, the disease can affect fruits, causing rot or the appearance of spots that make the produce unmarketable.

In the event of a mass infection outbreak, yield losses can range from 10% to 30%, depending on the crop, the stage of plant development, and seasonal weather conditions.

The basic method of control is crop rotation, which prevents the planting of a susceptible crop on the same field for at least 3–4 years, effectively interrupting the fungal life cycle in the soil.

It is necessary to ensure high-quality incorporation of post-harvest residues into the soil, as they are the primary reservoir of infection. Deep plowing promotes rapid decomposition of residues and the death of the pathogen.

The use of healthy, treated seed material is an effective protection method during early growth stages, preventing the infection of seedlings.

• Application of systemic fungicides during the active growth period.
• Cultivation of resistant or tolerant varieties and hybrids.
• Timely weed management to remove potential host plants.
• Optimization of plant stand density to improve aeration.

Field monitoring and the application of chemical control agents (fungicides based on triazoles or strobilurins) should be performed strictly upon the appearance of the first signs of the disease, adhering to pesticide application regulations.