Detection of viruses in special stands of common ash reveals insights into the virome of Fraxinus excelsior

Abstract

We report the results of a virus screening conducted on selected special stands of common ash (Fraxinus excelsior) within the FraxVir project. This project among others deals with the recording and assessment of the virus diversity in common ash and the impact of the ash virome on ash dieback diseased trees. Ash dieback, a fungal disease caused by the invasive fungus Hymenoscyphus fraxineus is a major threat to Fraxinus excelsior populations across Europe. Over three consecutive years, ash trees from different origins were tested including leaf material from mother trees and seedlings from the natural regeneration as well as fruits to gain insight into possible modes of virus transmission. Using RT-PCR, we screened for five viruses, including the generalist species arabis mosaic virus and cherry leaf roll virus, as well as newly discovered viruses in ash including an emaravirus, an idaeovirus and viruses of the cytorhabdovirus group. Amplification and comparison of PCR amplicons comprising the nucleocapsid region revealed sequence diversities that confirm two distinct cytorhadovirus species present in different populations of common ash. Signatures of novel viruses from different families have been identified by high-throughput sequencing. Together our results provide insights into the virus diversity and distribution of viruses in ash and expand our knowledge about the virome of this endangered tree species.