Antifungal activity of lichen extracts and lichenic acids

Acetone extracts of the three lichen species Evernia prunastri, Hypogymnia physodes and Cladonia portentosa were investigated for activity against eight plant pathogenic fungi: Pythium ultimum, Phytophthora infestans, Rhizoctonia solani, Botrytis cinerea, Colletotrichum lindemuthianum, Fusarium solani, Stagonospora nodorum and Ustilago maydis. Particularly, E. prunastri and H. physodes exhibit total or strong inhibition on P. ultimum, U. maydis and P. infestans growth. In contrast, Cladonia extracts were less active to reduce growth of these fungi. Lichenic acids were also examined for antifungal activity. P. infestans growth was severely inhibited by evernic acid. P. ultimum and P. infestans growth were slightly but significantly inhibited by evernic acid and (-) usnic acid, respectively. Growth inhibition of U. maydis was also observed for the latter lichenic acid. These results confirm the previously observed activities of lichen extracts. This suggests that secondary lichen metabolites might be of potential use as antifungal agents.