Filamentous Fungi Associated with Disease Symptoms in Non-Native Giant Sequoia (Sequoiadendron giganteum) in Germany—A Gateway for Alien Fungal Pathogens?

Filamentous fungi associated with disease symptoms in non-native giant sequoia (Sequoiadendron giganteum) in Germany were investigated in ten cases of disease in Northwest Germany. During the study period from 2018 to 2023, a total of 81 species of Dikaria were isolated from woody tissue and needles of giant sequoia and morphotyped. Morphotypes were assigned to species designations based on ITS-sequence comparison and, in part, multi-locus phylogenetic analyses. Nine species were recognised as new reports for Germany or on giant sequoia: Amycosphaerella africana, Botryosphaeria parva, Coniochaeta acaciae, C. velutina, Muriformistrickeria rubi, Pestalotiopsis australis, P. monochaeta, Phacidiopycnis washingtonensis, and Rhizosphaera minteri. The threat posed to giant sequoia and other forest trees in Germany by certain, especially newly reported, fungal species is being discussed. The detection of a considerable number of new fungal records in the trees studied suggests that giant sequoia cultivation may be a gateway for alien fungal species in Germany.