The paper discusses the cultivation of the mycelium of some economically significant xylotrophic basidiomycetes using methods of clonal micropropagation. For cultivation, Chapek, Murashige-Skoog synthetic synthetic media are used, a comparative analysis of mycelium growth in these media is carried out. Particular attention is paid to the study of the phytopathogenic properties of mycelium obtained in vitro. Two variants of phytopathogenicity are being studied: the cultural one, which is associated with the nature and intensity of mycelium growth on a nutrient medium, and phytopathogenicity for anatomical structures during the joint cultivation of xylotrophic basidiomycetes mycelium with parts of shoots from B. pendula and P. tremula . Significant variability was shown both in the expansivity of mycelial growth and in the manifestation of the degree of phytopathogenicity in different types of xylotrophs. Microscopy of the in vitro mycelium obtained was also carried out in order to more accurately identify the organism under study and to study the anatomical and morphological features. In general, this study will make it possible to better understand the ecology of these organisms in vivo, to model the interaction of the host parasite, and to more quickly and accurately conduct a specific determination of the phytopathogen, which can be used when conducting sanitary-protective and other economic activities in the forest industry.