# Characterization of a Novel Emaravirus Affecting Ash Species (_Fraximus_ spp.) in Europe
## 1 Introduction  
Although virus-like symptoms have long been observed in ash [1, 2], no viral agents affecting _Fraximus_ spp. have to date been studied in detail. The list of plant viruses known to infect ash comprises of generalist species including arabis mosaic virus (ArMV), cherry leaf roll virus (CLRV), tobacco necrosis virus (TNV), tobacco mosaic virus (TMV), tobacco rattle virus (TRV), tomato ringspot virus (ToRSV) and tobacco ringspot virus (TRSV) [3, 4]. Our investigations of _Fraximus_ spp. were instigated by current interest in ash dieback, a disease that has decimated populations of European ash (_Fraximus excisior_ L.) across the continent in recent years [5]. Although the disease is primarily thought to be caused bythe pathogenic fungus _Hymenoscyplus fraxineus_, the role of other biotic and abiotic stress factors, including viruses, in disease development remains to be investigated. Ash (_Fraxinus_ spp. ; Family: _Oleaceae_) is a group of broad-leaved, mostly deciduous trees, with both the European ash (_F. excelsior_) and the manna ash (_F. ornus_) being native to Europe. Not only do both species have important roles in primary or secondary succession stages in forest ecosystems, they also have a decorative, ornamental use in urban environments [6; 7; 8]. Manna ash trees, which are naturally found in the Mediterranean region, are being increasingly trialed in towns and cities due to their drought tolerance in the face of climate change [9; 10]. Manna ash trees also appear to be less susceptible to ash dieback [11]. The causal agents of virus-suspect symptoms in forestry and urban green spaces were for a long time unknown, their identification only being made possible with advances in molecular biology over the last decades. Although the focus of much research on plant viral pathogens has concerned important agricultural and horticultural crops including fruit trees [3], the increasing application of high throughput sequencing (HTS) technologies is revolutionizing the diagnosis and characterization of plant viruses [12; 13]. It is clear that a large uncharacterized forest tree virome is yet to be discovered [14]. HTS technologies have already been successfully used in the identification of a number of novel viruses in trees [15] and also in agricultural crops [16]. For instance, the virome of leaf roll diseased birch trees (_Betula_ spp.) was studied revealing several novel viruses belonging to different genera [17; 18]. Likewise, novel viruses of the genus _Emanavirus_ were discovered in pedunculate oak (_Quercus robur_) [19; 20] in sycamore maple (_Acer pseudoplatanus_) [21] and in Eurasian aspen (_Populus tremula_) [22] by Illumina RNASeq technology, applying total RNA extracted from diseased leaf material. The genus _Emanavirus_ (Order: _Bunyavirales_; Family: _Fimoviridae_) is comprised of viruses with a single-stranded (ss), segmented RNA genome in negative-sense orientation, which are typically transmitted by entiophyid gall mites [23; 24]. Other characteristics of emaraviruses include conserved, complementary terminal nucleotide sequences, enabling the circularization of genome segments and the formation of a panhandle structure [25], which is thought to be necessary for transcription and replication [26]. Spherical double membrane-bound bodies (DMBs) found in infected cells of host plants are also thought to represent the enveloped virus particles [24]. Since the description of the first member species _European mountain ash ringspot-associated emaravirus_ (EMARaV) and the establishment of the genus _Emanavirus_[24; 26], many other viruses have been assigned to the genus, currently numbering 21 [27]. Most emaraviruses have a narrow host range. Nevertheless, many of them cause economic losses in their respective natural host including important crops, or they could be associated with characteristic disease symptoms in herbaceous plants as well as in deciduous tree species [24]. However, prior to this study, no emaravirus species has been identified infecting _Fraxinus_ spp.