Antifungal and Profungal Potentials of Acetone-Extracted Complexes of Lichen Substances on Macromycete Heterobasidion parviporum Mycelium Growth Dynamics—The First In Vitro Approach

This study provides the first experimental evidence on how acetone-extracted lichen substances affect the mycelial growth of the pathogenic basidiomycete Heterobasidion parviporum. Six lichen species were tested: the terricolous species Cladonia arbuscula, C. digitata, C. rangiferina, C. uncialis and Cetraria islandica, and the epiphytic species Pseudevernia furfuracea. Extracts were prepared from single species and from species mixtures, including C. arbuscula + C. rangiferina + C. digitata and all five terricolous species. The substantial economic losses caused by the tested pathogen in forestry provided the rationale for these experiments. Two supplementation methods were used: applying extracts (1–4 mL) to solidified agar and incorporating extracts into the medium before solidification. The effects varied by extract, dose and supplementation method, showing either inhibitory or stimulatory potential. Surface application generally caused stronger inhibition than incorporation into the liquid medium, in which growth stimulation occurred, especially with extracts of C. rangiferina, C. digitata and Cetraria islandica. Fungistatic effects were associated mainly with usnic acid and, synergistically, with physodic acid, chloroatranorin and atranorin. The results highlight lichen extract complexes as promising eco-friendly biocontrol agents against H. parviporum in forest nurseries and spruce stands, with possible ecological implications.