Section outline
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AsMaV (genus Emaravirus, family Fimoviridae) is a single-stranded RNA virus with a negative orientation. Its genome consists of five RNAs. The RNA1 (7.1 kb) encodes for the viral RNA dependent RNA polymerase (RdRP, 268.2 kDa) and it is involved in virus replication. The RNA2 (2.3 kb), RNA3 (1.6 kb), RNA4 (1.6 kb), and RNA5 (1.3 kb) encode for the glycoprotein precursor (GPP, 73.5 kDa), viral nucleocapsid protein (NP, 35.6 kDa), a putative movement protein (MP, 41.0 kDa), and a protein of unknown function (P28, 28.1 kDa), respectively (von Bargen et al. 2020). Sequence comparisons of RNA1-RNA4 confirm that the virus is a member of the genus Emaravirus (von Bargen et al. 2020; Rehanek et al. 2022). Studies on the morphology of the virus are missing. However, it is likely that AsMaV forms spherical particles of varying size (80-100 nm) in the cytoplasm of infected mesophyll cells as described for other emaraviruses (Rehanek et al. 2022). The main routes of virus transmission have not been investigated in detail so far. As mechanical transmission of this virus appears to be difficult, vector transmission by different gall mite species found to be associated with the mosaic disease of aspen has to be considered responsible for the wide natural dissemination of AsMaV in Fennoscandia. Furthermore, vegetative transmission may play a role, as Eurasian aspen propagates effectively by root suckers (von Bargen et al. 2020). The natural host range of the virus remains to be determined as AsMaV was only confirmed in Eurasian aspen displaying characteristic symptoms. Other poplar species showing similar virus-like symptoms were found to be infected by other viruses such as poplar mosaic carlavirus (PopMV) (von Bargen et al. 2020; Büttner et al. 2023). Since interspecies hybrids of aspen and poplar occur quite frequently in nature and are also used in forestry, it can be assumed that the natural host range of the virus extends to species related to Eurasian aspen.
AsMaV-infected Eurasian aspen (P. tremula) showing extensive dieback of twigs and branches in the lower parts of the canopy