Planistromellosis

The first visual signs of planistromellosis appear as chlorotic spots on the leaf blades. As the mycelium develops, these spots acquire a necrotic coloration, turning brown or black.

A characteristic feature is the emergence of small dark dots on the affected areas — these are the fungal ascostromata. They may appear singly or in groups, creating a specific pattern corresponding to the leaf vein anatomy.

In areas of severe infection, the leaf tissue thins and may die prematurely. Necroses are often limited in shape, surrounded by a lighter halo, indicating the plant's attempts to localize the infection.

When stems are affected, shoot deformation and surface cracking can be observed. These injuries provide entry points for secondary infections, which significantly complicates the plant's overall health.

• Yellowing or browning of specific leaf sections.
• Formation of black dots (fruiting bodies) on necrotic lesions.
• Premature leaf drop.
• Stunted growth and impaired development of vegetative organs.

The disease is caused by fungi belonging to the family Planistromellaceae, within the order Dothideales and class Dothideomycetes. These are highly specialized ascomycetes, whose life cycles are closely tied to specific host plants.

A mycological feature of this taxon is the formation of unique stromatic structures. These fruiting bodies, known as ascostromata, develop within the plant epidermis tissue, making early detection difficult.

The pathogenic process begins when ascospores germinate on the surface of leaves or stems. The fungus hyphae penetrate the intercellular spaces, gradually breaking down the plant cell structure to extract nutrients.

Fungal reproduction occurs through the formation of sexual spores called ascospores, which are released into the environment under favorable conditions. The spread of the inoculum is primarily driven by wind and rain splashes.

In the life cycle of Planistromellaceae, there is often a strong association with plant debris. The overwintering stage of the fungus survives on fallen leaves and infected shoots, ensuring primary infection at the start of the next growing season.

Relative humidity is critical for the development of this disease. High humidity levels, exceeding 70–80%, create an optimal environment for spore germination and colonization of plant tissues.

Temperature is also a determining factor for Planistromellaceae activity. The most intense development of the pathogen occurs under moderately warm conditions typical of spring and early summer.

Crowded plantings and poor ventilation in agroecosystems facilitate rapid disease spread. Restricted air circulation prevents moisture from drying quickly on the leaf surfaces, creating a greenhouse effect.

Poor agricultural practices, such as the excessive application of nitrogen fertilizers, make plant tissues more succulent and vulnerable to pathogen invasion. Weakened plant immunity significantly increases the risk of mass infection.

Rainfall during the spore maturation period promotes their dispersal to healthy plants. Heavy rains alternating with sunny weather create ideal conditions for the spread of fungal diseases in orchards and crop fields.

The primary damage caused by planistromellosis is a significant reduction in the leaf surface area available for assimilation. The loss of chlorophyll leads to a disruption of photosynthesis, which directly impacts crop productivity.

As a result of impaired metabolic processes, the plant's ability to accumulate organic matter is reduced. This leads to yield losses, poor fruit quality, and a decrease in commercial marketability.

When perennial plants are affected, the disease contributes to the general decline of trees or shrubs. Chronic infection reduces winter hardiness, leaving plants susceptible to cold damage during winter.

Under epidemic conditions, mass dieback of young shoots and premature leaf drop may occur. This negatively impacts the formation of fruit buds for the following year's harvest.

Economic losses consist not only of yield reduction but also of the costs associated with implementing additional fungicidal treatments. Controlling resistant strains of the pathogen requires significant investment in crop protection products.

Prevention of planistromellosis begins with the thorough removal and destruction of plant debris. Since the pathogen survives on fallen leaves, their removal from the field or orchard is a priority sanitary measure.

Correct formative pruning is an essential technique. Creating an open canopy improves airflow and light penetration, which reduces humidity within the shrub or tree and hinders fungal development.

Fungicide application remains the primary control method in the event of an outbreak. It is recommended to use systemic products capable of suppressing ascomycete development during the early stages of symptom manifestation.

Balanced mineral nutrition, avoiding excess nitrogen in late summer, increases natural plant resistance to fungal infections. Phosphorus and potassium fertilizers strengthen cell walls, making it harder for pathogen hyphae to penetrate.

Using resistant cultivars and hybrids is the most reliable protection strategy. Breeding programs focus on developing plants with genetic immunity to specific types of pathogenic fungi in the Planistromellaceae family.