Endophytes in changing environments - do we need new concepts in forest management?

The occurrence of endophytic fungi, hosted by living tissues of forest trees seems to be a common phenomenon. Numerous studies show that these colonists are mostly symptomless or even live in a symbiotic relationship to the host plant. Our investigations on Douglas-fir and Rhabdocline needlecast show that Rhabdocline pseudotsugae (Sydow), which has been described exclusively as an obligatory needle pathogen up to now, is able to persist symptomless in different types of plant tissues and therefore an endophytic lifestyle has to be assumed. Whether this lifestyle is part of the infection strategy of the fungus is still unclear. However, examples of other wood associated fungi lead us to the hypothesis that environmental such as climate conditions are able to trigger the phenomenon of changing from a mutualist to a virulent parasite.