# Molecular Population Genetics of Aspen Mosaic-Associated Virus in Finland and Sweden
## 4 Conclusions  
Virus evolution involves changes in the genetic structure of a viral population over time, which begins with mutation, recombination, and reassortment. Then, host and vector factors, along with selection pressures, expose plant viruses to genetic drift, leading to the emergence of new viral strains or species with novel biological properties. Some viruses adapt to specific hosts or groups of hosts, while some can adapt to diverse hosts, vectors, and environments [23; 24; 25]. Therefore, studying the genetic diversity of viruses is important. Our understanding of the role of viruses in wild plant populations is improving, and we are beginning to understand how viruses affect the invasiveness of introduced plant species [66]. Since the wild trees, especially old ones, could survive even after being infected with viruses, we might consider these long interactions as symbiosis or tolerance of the wild trees to cope with these infections. However, viruses could also cause a decline in trees [67]. Most of the reported emaraviruses are attacking forest trees [6]. Our findings resolved that AsMaV-NP is the suitable candidate for genetic diversity studies of this virus since phylogenetic analysis based on full-length RNA3 or NP sequences resulted in similar profiles, and could discriminate the AsMaV isolates better than other genomic regions under investigation in this study. These results support the idea that the NP protein is a good representative of AsMaV genetic diversity studies. Although the RT-PCR-RFLP with AanI profiling did not correlate with the geographical origin of the isolates, it identified different haplotypes in Kuninkaansaari and Vallisaari islands, indicating the presence of multiple virus isolates in these islands as a hotspot for emerging new isolates. In addition, the number of the restriction site of AanI could be a landmark of emerging more divergent isolates of AsMaV since the isolates E58627, E58632, E58213, and E57260 were separated from other isolates of AsMaV in different phylogenetic trees. However, these were signals of recombination or reassortment in the phylogenetic trees based on different genomic regions of AsMaV isolates, thus, RDP analyses were not able to offer strong evidence. There is a need for sequence data from other geographical areas to obtain a better understanding of recombination events in AsMaV isolates. Recombination and reassortment would be also a mechanism involved in emerging new isolates, especially in the case of multipartite plant viruses [68] such as tospoviruses [69], and the cucumber mosaic virus (CMV) [19; 20]. There are different reports on the frequency of reassortment in natural populations of plant viruses [19; 20]. In the case of emaraviruses, it has been suggested that certain FMV strains may have emerged through reassortments of genomic RNAs from different isolates [30]. It has been shown that recombination and reassort play an important role in the diversity of HPWMoV [39]. Therefore, it can be concluded that there is a need of sequence data from more AsMaV isolates, especially from more geographical regions. The genetic diversity parameters suggest that the Finnish population has higher genetic diversity compared to the Swedish population in all three analyzed genomic regions and these regions are under purifying selection. There is evidence of high selection pressure on AsMaV genome, but which was not consistent across different genomic regions. This pressure was almost equal on the N terminal region of RdRP (0.40) and MP (0.49), but it was at least five time less for NP (0.21). The nucleotide diversity of RNA3 and RNA4 of AsMaV were 0.059 and 0.32, respectively, which is higher than those reported for FMV (0.022 and 0.023) [30]. This range of nucleotide diversity was in a similar range for some other woody plant-invading viruses, such as CTV (0.038) and citrus leaf blotch virus (0.021) [30; 70; 71] but very low in comparison to grapevine fanleaf virus (0.15) [11; 30; 72; 73].