Microstrobilinia castrans, a new genus and species of the Sclerotiniaceae parasitizing pollen cones of Picea spp.

Abstract

AbstractThe fungal pathogens of spruce are well known in Europe and elsewhere. Therefore, it was surprising to discover a new fungal species and genus in Central Europe that attacks the pollen cones of three spruce species. The new ascomycete forms apothecia on stromatized pollen cones of Norway spruce (Picea abies) and Serbian spruce (Picea omorika) in mountain areas and on West Himalayan spruce (Picea smithiana) planted in urban lowland regions of Switzerland, Germany, and Italy. It was also detected in France, based on metabarcode sequences deposited in the GlobalFungi database. Its sudden appearance and the different origins of the host trees in Europe and Asia leave the origin of the fungus unclear. The new fungus might be a neomycete for Europe. A phylogenetic analysis using SSU, LSU, ITS, RPB2, and TEF1 sequences classified the fungus as a member of Sclerotiniaceae (Helotiales, Leotiomycetes). However, it differs morphologically from the other genera of this family in having an ascus without apical apparatus containing four mainly citriform spores with 16 nuclei each. Furthermore, it is the only known cup fungus that parasitizes pollen cones of conifers by stromatizing their tissue and infecting pollen grains. The fungus does not seem to cause major damage to the spruce populations, as only a few pollen cones per tree are affected. All this leads us to describe the newly discovered fungus as the new species and new genus Microstrobilinia castrans, the fungus that castrates pollen cones of spruce.