Investigating Host Preference of Root Endophytes of Three European Tree Species, with a Focus on Members of the Phialocephala fortinii - Acephala applanata Species Complex (PAC).

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.