Species and genetic variability of sweet potato viruses in China

China is the world's largest producer of sweet potato (Ipomoea batatas (L.) Lam.). Considering that there are numerous sweet potato-producing regions in China and sweet potato is a vegetatively propagated crop, the genetic diversity of sweet potato viruses could be high in the country. However, studies on species and genetic variabilities of sweet potato viruses in China are limited, making it difficult to prevent and control viral diseases in this crop. During 2014-2019, sweet potato samples with viral disease-like symptoms were randomly collected from sweet potato fields in 25 provinces in China. Twenty-one virus species, including 12 DNA and 9 RNA viruses, were identified in the samples using next-generation sequencing, polymerase chain reaction and rolling-circle amplification methods. One novel sweepovirus species, Sweet potato leaf curl Hubei virus (SPLCHbV), was identified. Two species, Sweet potato collusive virus and Tobacco mosaic virus, were identified for the first time in sweet potato in China. Full-length or nearly full-length genomic sequences of 111 isolates belonging to 18 viral species were obtained. Genome sequence comparisons of potyvirus isolates obtained in this study indicate that the genome of sweet potato virus 2 is highly conserved, whereas the other four potyviruses, sweet potato feathery mottle virus, sweet potato virus G, sweet potato latent virus and sweet potato virus C, exhibited a high genetic variability. The similarities among the 40 sweepovirus genomic sequences obtained from eight sweepovirus species are 67.0-99.8%. The eight sweepoviruses include 14 strains, of which 4 novel strains were identified from SPLCHbV and 1 from sweet potato leaf curl Guangxi virus. Five sweet potato chlorotic stunt virus (SPCSV) isolates obtained belong to the WA strain, and the genome sequences of SPCSV are highly conserved. Together, this study for the first time comprehensively reports the variability of sweet potato viruses in China.