Evidence for an Asian origin of Sorghum Mosaic Virus Infecting Sugarcane in Louisiana and the Western Hemisphere.

Three viruses causing mosaic-like symptoms in sugarcane and related grasses, namely sorghum mosaic virus (SrMV), sugarcane mosaic virus (SCMV), and sugarcane streak mosaic virus (SCSMV), have been reported in Louisiana since 1919. In this study, complete genome-coding sequences (9168-9240 nt) were obtained for mosaic viruses from 36 symptomatic leaf samples of cultivated and wild sugarcane and one sample of silver grass. These samples represented historical diseased plants that were collected in Louisiana from the 1940s to the early 2020s. SrMV sequences were obtained from 35 sugarcane samples whereas a SCMV sequence was recovered from one. Miscanthus sinensis mosaic virus (MsiMV) was identified in the silver grass sample. Virus populations of SrMV from the USA and from China differed based on phylogenetic investigations of the complete genome-coding sequence of 59 virus isolates. Recombination events and the greater diversity of SrMV in China suggested that the virus occurring in the USA originated from Asia. All SrMV isolates from the Americas (Argentina, Louisiana, Paraguay, and Texas) also grouped together in a phylogenetic tree based on the coat protein sequence of 683 worldwide virus isolates. These isolates of the Western Hemisphere differed from the isolates from Asia (China, Myanmar, and Vietnam). The isolates of SrMV from the USA, including pathogenic strains H, I, and M, belonged to the same phylogenetic lineage, thus suggesting that the pathogenic variation of the virus needs further investigations and application of strict quarantine measures to avoid further spread of SrMV among sugarcane-producing locations.