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 (<i>Sequoiadendron giganteum</i>) 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: <i>Amycosphaerella africana</i>, <i>Botryosphaeria parva</i>, <i>Coniochaeta acaciae</i>, <i>C. velutina</i>, <i>Muriformistrickeria rubi</i>, <i>Pestalotiopsis australis</i>, <i>P. monochaeta</i>, <i>Phacidiopycnis washingtonensis</i>, and <i>Rhizosphaera minteri</i>. 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.