Phoma piskorzii

The causal agent of this disease is the fungus Phoma piskorzii, which belongs to the class of deuteromycetes. It is a pathogenic microorganism that primarily infects the tissues of various agricultural crops, causing necrotic processes and disrupting normal plant metabolism. The fungus survives through conidia, which persist in crop debris and soil for extended periods of time.

The primary hosts for this pathogen include members of the Asteraceae family. The disease is frequently observed on sunflowers and certain ornamental floral crops. The pathogen can attack stems, leaves, and the root system, leading to a significant weakening of the plant and a decrease in productivity during the growing season.

Symptoms of the infection manifest as dark, usually brown or black lesions on stems and leaf petioles. As the infection progresses, the affected tissues begin to decay, creating distinct ulcers. On the surface of these lesions, one can often observe small black dots — pycnidia, where fungal spores develop, ensuring the further spread of the pathogen.

The development of Phoma piskorzii is favored by high humidity conditions and moderate air temperatures ranging between 20–25°C. Heavy rainfall, the presence of surface moisture, and dense crop canopies create an ideal environment for rapid spore germination and the infection of neighboring plants. In field conditions, the infection is easily dispersed by wind, rain splashes, and farm machinery operations.

The economic impact of the disease stems from the disruption of photosynthesis and nutrient transport within the plant. Severe infections lead to premature wilting, stem lodging, and poorly developed seeds, resulting in critical crop yield losses. Preventive measures include the use of resistant varieties, strict adherence to crop rotation, deep incorporation of crop residues, and timely application of fungicides to the fields.