Are endophytic fungi from Rhododendron tomentosum preadapted for its essential oil?

Endophytic fungi have to cope with various secondary metabolites produced by their host plant. Rhododendron tomentosum is an evergreen shrub with a high content of essential oil showing antimicrobial effects. The first aim of our study was to reveal the diversity of culturable endophytic fungi colonizing leaves of R. tomentosum. We isolated and identified 30 species, mostly ubiquitous species colonizing various plants as endophytes and later turning into saprotrophs. The second aim was to explore whether strains obtained from R. tomentosum (RT-strain) are better adapted to growth in environments with essential oils, compared to strains of the same species obtained from different substrates. In five of the six species pairs tested, the growth of RT-strains was more inhibited by three components of the essential oil added to the medium, compared to the corresponding strains. Only the RT-strain of Desmazierella acicola was less susceptible compared to its corresponding strain. Our results show that the essential oil in leaves of R. tomentosum do not represent a selective barrier that can be crossed only by preadapted strains.