# Characterization of a Novel Emaravirus Affecting Ash Species (_Fraximus_ spp.) in Europe
## 4 Discussion
Symptoms of chlorotic ringspots, mottle and line pattern are typical of many other emaravirus infections, including rowan (_Sorbus aucuparia_ L.) infected with European mountain ash ringspot-associated virus (EMAReV) [3; 26]. Many emaravirus-infected plants are also known to suffer a general decline over time, often leading to their eventual death [3; 41; 53]. Although several ash trees displaying premature leaf loss and branch dieback were observed during field excursions, these symptoms were most likely attributed to the fungus _Hymenoscyplus frazimus_ responsible for the ash dieback disease. This remains to be determined for ASaV-infected ash. Interestingly, a range of leaf deformations, from curling to a severe narrowing of the leaflets known as shoestring, were also found to be associated with the presence of the virus in ash. Although symptom severity is likely a function of the developmental stage of the host at the time of infection and length of infection, [PERSON] et al. [54] reported that symptom severity in rowan was not correlated with the EMAReV titer, as might be expected if this were the case. Symptom expression in the infected rowan was also found to vary over consecutive seasons. Virus strain and virulence, tolerance of the host plant and even differences in environmental conditions are factors likely to affect symptom development. Despite the absence of further sequences of known viruses in HTS datasets, [PERSON] postulates establishing a direct causal link between ASaV and the disease symptoms have yet to be fulfilled. The difficulty of isolating the necessary infectious emaravirus particles to achieve this is well known [24]. The use of infectious full-length ASaV clones or graft transmission studies, as outlined by [PERSON] et al. [22] and [PERSON] [55], would provide conclusive evidence of ASaV as the cause of the disease in previously healthy host plants. ASaV was also detected in a number of trees displaying no observable symptoms, thus confirming a latent infection of _F. excelsior_ and _F. ornus_. Latent emaravirus infections have been documented for a number of other emaraviruses, including rowan infected with EMAReV [54] and pear infected with pear chlorotic leaf spot associated virus (PCLSaV) [56]. It is currently unclear whether the infected ash lacking disease symptoms were simply sampled at an early stage of infection and may have exhibited ASaV-related symptoms at other timepoints over the vegetation period or whether they remained latent, with disease development possibly only being induced during the influence of additional abiotic or biotic stress factors, for instance fungal infections. ASaV infections were found to be widespread across Europe, ranging from Southern Sweden in the north to Bolzano, Northern Italy in the south. The native habitat of both host _Frazimus_ species, however, extends much further than the investigated area covered in this study, which is particularly true for _F. ornus_, which is native to the Mediterranean region [6]. These preliminary findings suggest however that ASaV is likely to be present throughout its host's range. As other emaraviruses have been found to infect more than one host species, the possibility of ASaV infecting additional _Frazimus_ spp., including non-native ornamental species such as the red ash (_F. pennsylvania_), is possible. EMAReV, for example, is known to infect several closely related species and interspecies hybrids of the family _Rosaceae_[26; 28; 57; 58; 59]. A European-wide ASaV monitoring would most probably reveal a more extensive geographical distribution and additional host species of the novel virus ASaV. Preliminary sequence data based on partial RNA3, 4 and 5 sequences, suggest a high level of genetic identity of ASaV at both the nucleotide and the amino acid level. There also appears to be no correlation between genetic variability and either host species or geographical location of trees sampled.