3.4 Genetic and phylogenetic analysis
The σC genes of both newly identified NDRV isolates were 1568 bp in length. To further investigate the genetic characteristics of both newly isolated NDRV strains, their σC genes and induced amino acid were compared with reference WRV strains. According to the sequence alignment of σC genes, Nucleotide identity between HNXX-1/2021 and HNJZ-2/2021 was 99.1%, which shared 98.4% and 98% identities with DRV/SY/Jiangsu/2018 in nucleotide, and 98.8% and 99.1% in deduced amino acid, respectively. Meanwhile, HNXX-1/2021 and HNJZ-2/2021 shared 98.4% and 98% in nucleotide, 98.5% and 98.8% in deduced amino acid with DRV/SDHZ17/Shangdong/2017, respectively. The nucleotide sequences of the σC gene of HNXX-1/2021 and HNJZ-2/2021 were deposited into GenBank (accession numbers: ON012751 and ON012752).
To further explore the evolutionary characters of the newly identified NDRV strains, the phylogenetic tree of NDRVs was constructed based on the σC genes deduced amino acid sequences (Figure 3). As shown in the phylogenetic tree, HNXX-1/2021 and HNJZ-2/2021 were clustered together with DRV/QR/Hubei/2020, DRV/GX-Y7/Guangxi, DRV/SDLY18/Shandong/2018 and DRV/SY/Jiangsu/2018, Which were NDRV strains emerged in recent years in China.
Remarkably, all the DRVs strains were clustered into two distinct clades. Clade1 comprised the majority of DRVs strains that emerged before 2017, and few strains only emerged in Shandong province after 2017. Clade 2 comprised the majority of the NDRV strains that emerged after 2017, including the newly identified NDRV strains HNXX-1/2021 and HNJZ-2/2021 in this study.