3.6 Sequence comparison and phylogenetic analysis
The comparison of nucleotide sequence similarity between the N-DRV-SD19 strain and the reference strain (from GenBank) shows that the similarity between N-DRV-SD19 and N-DRV-XT18 was 100%. The sequence similarities between N-DRV-SD19 and other waterfowl-derived strains isolated in China (except N-DRV-XT18) were 96.2-97.8%, while that with chicken-derived isolates was 37.5-40.6%, and that with mammalian isolates was 27.1-36.0%. To investigate the evolutionary relationship between N-DRV-SD19 strain obtained in this study and other Orthoreovirus strains, based on the nucleotide sequence of the S1 gene fragment, we constructed phylogenetic tree using neighbor-joining method (Chen et al., 2020). The analysis results show that SD19 strain was located in in the same evolutionary branch as the novel duck-derived ARV variant N-DRV-XT18 previously reported. In addition, the N-DRV-SD19 was in the same phylogenetic lineage with these strains isolated from Chinese duck flocks in recent years (Fig. 4). It should be noted that although they are both waterfowl-derived strains, the strains isolated in China are far from the D20-99 strain isolated from Hungary.