Inoculation success of Inonotus obliquus in birch and alder sites in Estonia

Abstract Inonotus obliquus (commonly known as Chaga) is a medicinal fungus traditionally harvested from birch trees but increasingly explored for artificial cultivation due to rising commercial demand. This study evaluates the inoculation success of I. obliquus in four broadleaved tree species—Betula pendula, B. pubescens, Alnus incana, and A. glutinosa—under field conditions in Estonia, using nine genetically different Inonotus obliquusfungal strains. The experiment was conducted at two locations in Estonia, encompassing a total of six forest sites, with inoculation success assessed two years after inoculation using species-specific qPCR. Inoculation success varied by location, with a higher infection rate (18%) observed at Järvselja compared to Võrumaa (3%). Among the tested fungal strains, three—PAT24473, PAT24478, and PAT22865—consistently achieved higher infection rates. Notably, sterile conks developed only on A. glutinosa trees four years after inoculation in tested sites and with strains PAT24474, PAT24478, and PAT22865. Only fungal strains had a statistically significant effect on infection probability. Host species, tree diameter, and pre-existing wood decay had no statistically significant effects on inoculation success, and visible stem symptoms were unreliable indicators to estimate infection rate. These results highlighting the importance of molecular diagnostics to test inoculation success, and it suggests that alders - particularly A. glutinosa, could be as viable as birches for cultivation of I. obliquus.