Аннотация
This study evaluated the antagonistic activity of Trichoderma harzianum against phytopathogenic fungi of the genus Cytospora, which cause necrosis and dieback in fruit and forest tree species. Morphological characterization of T. harzianum cultures revealed typical structures and intensive sporulation of the mycelium, ensuring rapid colonization of the nutrient medium. During dual culture, pronounced inhibition of the pathogens C. chrysosperma, C. sorbina, C. parasitica, and C. pruinopsiswas observed, manifested by changes in mycelial pigmentation, restricted colony development, and displacement of the pathogens from the central zones of Petri dishes. By the eighth day of incubation, the growth of Cytospora phytopathogens was suppressed by the antagonist T. harzianum, accompanied by active sporulation. Molecular identification based on ITS-region analysis confirmed that the isolates belonged to T. harzianum (100% identity with GenBank data). The constructed phylogenetic tree showed clear clustering of the isolates within the T. harzianum taxonomic group with high bootstrap support. The results confirm that T. harzianum is a promising biological control agent against Cytospora fungi and highlight the importance of an integrated approach combining morphological and molecular–genetic analyses in studies of antagonistic properties.