# Molecular Population Genetics of Aspen Mosaic-Associated Virus in Finland and Sweden
## 1 Introduction  
Aspen trees (_Populus tremula_) are widely distributed across Europe and play an important ecological and economic role in the region. These trees are particularly abundant in Northern Europe, including Finland, and Sweden. Aspens are known for their adaptability, fast growth, and ability to colonize disturbed areas [1]. They also provide a wide range of ecosystem services, including habitats for wildlife, carbon sequestration, soil stabilization, and water regulation [2; 3; 4]. In addition to their ecological significance, aspen trees have cultural and historical importance to people worldwide. In addition to fibers being used in the production of pulp as strand board, solid wood, and furniture, aspen wood is used in many specialty products, for instance, pencils, skis, sauna benches, and coffins [2]. Recently, it has been reported that aspen mosaic-associated virus (AsMaV) is associated with leaf symptoms, such as mottle, yellow blotting, variegation, and chloroses along veins [5]. Our surveys of many years have led to the conclusion that the virus is probably associated with the decline in aspen trees [5]. AsMaV is a member of the virus genus _Emanavirus_, which includes other plant pathogens such as the European mountain ash ringspot-associated virus and the rose rosette virus [6]. AsMaV has a segmented negative-sense single-stranded RNA (\(\approx\)sRNA) genome designated as RNA1-RNA5. The genome ofAsMaV consists of five \(-\)ssRNA molecules. 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 [5]. RNA viruses, which account for the majority of plant viruses, have high mutation rates due to the error prone nature of viral replicase or RdRP followed by other mechanisms such as recombination and reassortment [7; 8; 9; 10; 11]. The introduced mutations during the replication cycle of a virus are mostly deleterious for the virus, but sometimes they may lead to the generation of new isolates with altered phenotypes, such as host range, symptom severity, and transmission efficiency [12; 13; 14; 15; 16; 17]. The effect of these phenomena in shaping of plant viruses has been reviewed [18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. The genetic diversity of plant viruses is important for understanding their evolution, spread, and potential of emerging new isolates may that are resistant to existing control measures. The genome of the emaraviruses consist of at least four \(-\)ssRNA (RNA1-4, core genome) but could extend to twelve segments [6; 28]. The genetic diversity of a few members of emaraviruses, including fig mosaic virus (FMV) [29; 30], blackberry leaf mottle-associated virus (BLMaV) [31], maptle-associated virus (MaMaV) [32], raspberry leaf blotch virus (RLBV) [33; 34], rose rosette virus (RRV) [35], jujube yellow mottle-associated virus (JYMaV) [36], Perilla mosaic virus (PerMV) [37], European mountain ash ringspot-associated virus (EMAReV) [38], and High Plains wheat mosaic virus (HPWMoV) [39], has been studied. These studies have utilized one or more partial or complete viral genomic RNA(s), among which RNA3 has been identified as the main genomic region for studying the genetic diversity of emaraviruses followed by RNA4 and partial RNA1, all belonging to the core genome of emaraviruses. It should be mentioned that NP has been used not only in the genetic diversity of emaraviruses but also in all \(-\)ssRNA viruses [40; 41; 42; 43]. Moreover, the NP is important in immunological tests for the identification of \(-\)ssRNA viruses and has been used in human [44] and plant viruses such as emaraviruses [45].