Plurivorosphaerella

The primary sign of infection is small chlorotic spots that eventually turn brown or dark brown with a distinct dark border.

On the necrotic areas of the leaf, small black dots often form — pycnidia (organs of asexual sporulation), which are clearly visible when examined with a magnifying glass.

In high humidity conditions, a faint grayish coating may appear around the spots, representing a mass of pathogen conidia.

As the disease progresses, individual spots may coalesce, covering large areas of the leaf blade, leading to premature yellowing and leaf death.

Another characteristic sign is the infection not only of leaves but also of petioles, and in some cases, stems, which causes general growth inhibition of the crop.

The disease is caused by a fungus belonging to the genus Plurivorosphaerella. It is a microscopic ascomycete that belongs to a group of pathogens causing septoria-like leaf spots on various agricultural crops.

The fungus lives as a parasite, specializing in the tissues of leaves and stems. Its life cycle includes both asexual reproduction via conidia and the formation of fruiting bodies known as pseudothecia.

Taxonomically, this pathogen is closely related to a complex of fungi that cause leaf spots and is often classified based on molecular genetic studies of ribosomal DNA.

The fungal mycelium develops primarily in the intercellular spaces of the host plant tissue, gradually destroying parenchyma cells to obtain nutrients.

During its life cycle, the pathogen releases specific metabolites that promote necrosis of plant tissues, creating the characteristic clinical picture of the disease.

The development of the disease depends directly on the hydrothermal conditions of the environment. Optimal conditions include moderate temperatures between 18–24°C and high air humidity.

Heavy rainfall, dew, and frequent fog create an ideal environment for spore germination and their subsequent spread across the field via rain splashes and wind.

The presence of liquid moisture on the leaf surface for several hours is critical for the successful infection of the host plant by fungal conidia.

The infectious background significantly increases if crop residues from the previous harvest remain in the field, as the pathogen survives on them during the winter.

Dense crop stands and poor aeration within the plant canopy facilitate the rapid spread of infection from diseased plants to healthy ones.

Plurivorosphaerella causes significant economic damage by reducing the total assimilation surface area of the leaves, leading to a decrease in photosynthesis intensity.

Severe crop infestation causes premature leaf drop, preventing the plant from accumulating sufficient nutrients to form a high-quality yield.

In the case of cereal or industrial crop infection, this leads to a reduction in thousand-kernel weight, deterioration of product quality, and loss of commercial appearance.

The disease significantly weakens the plant's immune system, making it more vulnerable to secondary pathogens and unfavorable abiotic environmental factors.

Under epiphytotic conditions, yield losses can range from 15 to 40% depending on the plant variety, weather conditions, and the timeliness of protection measures.

Effective protection is based on crop rotation, ensuring that susceptible crops are not returned to the same field for at least 3–4 years.

An important agrotechnical method is the deep incorporation of crop residues into the soil, where they decompose faster due to soil microflora activity.

• Using pathogen-resistant varieties and hybrids;
• Spatial isolation of crops from infected areas;
• Timely removal of weeds that can serve as infection reservoirs.

Application of fungicides from the triazole and strobilurin groups effectively inhibits fungal development when symptoms are detected early.

Regular field monitoring during critical plant growth stages is recommended to make informed decisions regarding the need for chemical treatment.