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The 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.

Host preference of root endophytes of the three European tree species of Norway spruce (Picea abies), common ash (Fraxinus excelsior), and sycamore maple (Acer pseudoplatanus) were investigated in two forest stands near Zurich, Switzerland. The focus was placed on members of the Phialocephala fortinii s.l. (sensu lato)—Acephala applanata species complex (PAC), as well as other dark septate endopyhtes (DSE). PAC species were identified based on 13 microsatellite loci. Eleven PAC species were found, with Phialocephala helvetica, P. europaea being the most frequent. All but cryptic species 12 (CSP12) preferred Norway spruce as a host. Though very rare in general, CSP12 was most frequently isolated from maple roots. Regarding the abundant PAC species, P. helvetica and P. europaea, the preference of spruce as a host was least pronounced in P. europaea, as it was also often isolated from ash and maple. It is the first record of PAC found on common ash (Fraxinus excelsior). Cadophora orchidicola, a close relative of PAC, has frequently been isolated from ash. Various species of the Nectriaceae (Cylindrocarpon spp.) have often been isolated, particularly from maple roots. By comparison, Pezicula spp. (Cryptosporiopsis spp.) was found to be abundant on all three hosts. Phomopsis phaseoli exhibits a clear preference for spruce., Journal of Fungi, 7 (4), ISSN:2309-608X

Members of the Phialocephala fortinii s.l. – Acephala applanata species complex (PAC) are ubiquitous endophytes forming complex communities in roots of conifers and ericaceous shrubs across the Northern hemisphere. Two kinds of disturbances (clear-cutting and drought) and their effects on the resident PAC community, as well as on the introduction of alien strain 7_45_5, were investigated using mesocosms with natural Norway spruce ( Picea abies ) regeneration, both under controlled climate chamber conditions and natural conditions in the forest. This is the first record of successful strain introduction into a well-established forest ecosystem. Introduction was more successful when planting inoculated living spruce saplings, compared to inoculation using autoclaved colonized roots. 7_45_5 was less assertive in the forest, where Phialocephala subalpina clearly dominated. Clear-cutting favored A. applanata and simultaneously reduced the overall frequency of PAC. Drought only had a significant influence on 7_45_5, which was more abundant in dry than moist, non-clear-cut plots. To conclude, disturbances and arrival of foreign strains can alter resident PAC communities significantly.

The effects of irrigation on colonization of Pinus sylvestris and Quercus pubescens by members of the Phialocephala fortinii s.l. – Acephala applanata species complex (PAC) was assessed. Roots were collected from an irrigation experiment site. PAC species were identified based on 13 microsatellites. Irrigation and host species had a significant effect on the frequency of roots colonized by PAC. In oak (Q. pubescens) but not in pine (P. sylvestris), PAC were significantly more common on dry non-irrigated plots than on irrigated ones. Frequency of colonization of pine roots was twice as high as that of oak roots, and the mean number of PAC species per tree was significantly higher for pines. A hitherto unknown PAC species was found. The community structure was random except for the most frequently isolated Phialocephala europaea and Phialocephala helvetica, which inhibited one another in pine roots. The possible effects of PAC colonization on drought resistance of oak are discussed.

Dark septate endophytes of the Phialocephala fortinii s.l. - Acephala applanata species complex (PAC) are presumed to be the most abundant root colonizing endophytes of conifers across the Northern hemisphere. To test the competitiveness of different PAC strains, PAC-free Picea abies saplings were inoculated with five different PAC strains by planting them in pre-colonized substrates. Saplings were left to grow for six weeks and then transplanted crosswise into a substrate colonized by one of the other four strains for a further two weeks. PAC were isolated and genotyped using microsatellite markers. The power of colonization, i.e. the ability of colonizing roots already colonized by another PAC strain, and the power of retention, i.e. the ability of a resident strain of not being suppressed by an invading PAC strain, were calculated for each strain in every combination. The experiment was run twice under two different climatic conditions. Our results show that PAC strains differ (1) in their ability to colonize PAC-free, non-sterile roots, (2) in resistance against being suppressed by another PAC strain and (3) in their ability to invade roots already colonized by another PAC strain. In addition, both the PAC-PAC and the PAC-host interactions depend on the climatic conditions.