First Report of Natural Infection of Potato virus M on Tobacco ( Nicotiana tabacum ) in China

Tobacco (Nicotiana tabacum), an annual or limited perennial herbaceous plant belonging to the family Solanaceae (Zou et al. 2021), holds significant economic value. In recent years, it has been threatened by various viral diseases. Viruses reported to infect tobacco include Tobacco mosaic virus, Cucumber mosaic virus, Potato virus Y, and others. The infection of these viruses severely impairs both the yield and quality of tobacco, sometimes causing devastating economic losses and hindering the high-quality development of the entire tobacco industry. Potato virus M (PVM) is an important pathogen of potato (Solanum tuberosum L.), causing yield losses and tuber quality reduction (Xu et al. 2010). It is a member of the genus Carlavirus (family Betaflexiviridae) with a single-stranded, positive-sense RNA genome (Su et al. 2017). PVM has a relatively wide host range primarily within the family Solanaceae, including potato, tomato, and some Nicotiana species (Tatarowska et al. 2020). Tobacco (Nicotiana tabacum) and N. benthamiana are well-documented experimental hosts for virus maintenance and study, which often exhibit mild or latent infections upon artificial inoculation. However, natural infection of PVM in tobacco has not been reported. In May 2023, in a commercial field in Yuxi Prefecture, Yunnan Province, China, approximately 5% of tobacco plants were observed to show mild mosaic, chlorotic mottling, and slight leaf distortion. To ensure representativeness, multi-point sampling was conducted for symptomatic plants in Yuxi City. Three representative leaves with typical symptoms were collected from different parts of the plants, and detection was performed using a PVM-specific enzyme-linked immunosorbent assay (ELISA) kit. Healthy tobacco leaves were used as the negative control, while PVM-infected pepino leaves served as the positive control. The ELISA results showed that all symptomatic leaf samples tested were positive for PVM. To further confirm the presence of PVM in tobacco, total RNA was extracted from five representative PVM-positive samples and subjected to RT-PCR using specific primers (Supplementary Table.1) targeting the coat protein (CP) gene of PVM. An 861-bp fragment, consistent with the expected size, was successfully amplified from all tested samples, and the corresponding isolate was designated as PVM-SLS. The full-length genome of PVM-SLS was obtained by Sanger sequencing (Supplementary Table.2) technology and the genome size of PVM-SLS was 8794 bp (GenBank accession: OR906323). Multiple sequence alignment of the viral polyprotein showed that PVM-SLS shared 43.2% to 96.3% amino acid sequence similarity with other PVM isolates (Glasa et al. 2019). A phylogenetic tree constructed based on the CP gene showed that PVM-SLS clustered independently of other PVM isolates and shared a nucleotide sequence similarity of 90.39% and a sequence coverage of 96% with the known isolate M57 (AY311395). In summary, while PVM infection and detection in potato have been extensively studied, no prior reports of its natural infection in tobacco have been documented. This study, by combining ELISA and RT-PCR with specific primers, demonstrates the natural infection of tobacco by this PVM-SLS isolate. To our knowledge, this is the first report of Potato virus M infecting tobacco. These findings provide a crucial basis for the prevention and control of viral diseases in tobacco.