EN
In the nurseries, Scots pine seedlings that show symptoms of the damping−off usually die. Rhizoctonia solani, a rapidly growing fungus, is one of the pathogens that infect the roots of plants. The aims of this study were: (1) to evaluate the susceptibility of R. solani and saprotrophic fungi Mortierella elongata, Trichoderma hamatum and T. rossicum to fungicides, (2) to determine whether yeast isolates can be used as effective inhibitors of the pathogen's growth, and (3) to analyze phylogenetic relationships between filamentous fungi. The Switch 62.5 WG fungicide, containing cyprodinil and fludioxonil, most effectively suppressed the growth of the tested R. solani isolates, but also exerted ecotoxic effects on the analyzed saprotrophs. The R. solani RS 1 isolate did not respond to the presence of azoxystrobin in PDA. Most of the 13 yeast isolates tested in the study inhibited the growth of pathogen colonies, but only one isolate was characterized by inhibitory activity of 59.03% and exerted a strong antagonistic influence on the pathogen. A phylogenetic analysis revealed that the tested isolates represented three clades: 1) T. hamatum, 2) T. rossicum, and 3) R. solani. The phylogenetic tree of M. hamatum and T. rossicum showing their divergence due to mutations did not reflect their speciation.