Natural Occurrence of Potato virus Y on Tomatillo ( Physalis philadelphica ) in China

In August 2023, a field survey was conducted in Jianshui County, Yunnan Province, China, with the purpose of assessing viral diversity in tobacco and its associated weeds. During this survey, we collected three tomatillo (Physalis philadelphica L.) plants (designated as JS1-JS3) from areas adjacent to tobacco fields, and these plants exhibited suspected viral symptoms such as mosaic, mottling and leaf deformation. The observed disease incidence was approximately 30%. Tomatillo is an annual herbaceous plant native to the Americas. It is commonly found in grasslands, on roadsides, and along field edges, and while also being cultivated in other tropical and subtropical regions worldwide (Kumar et al., 2024). To identify potential viral pathogens, three tomatillo samples (JS1-JS3) were pooled and subjected to total RNA extraction using TRIzol® reagent (Invitrogen, CA, USA), followed by RNA-Seq analysis on the Illumina NovaSeq platform. Following adapter trimming and quality filtering of the raw reads, 33,323,630 high-quality clean reads were obtained and assembled into 55,434 unigenes using Trinity software (v2.15.1). The unigenes were aligned, resulting in 58 contigs mapped to RNA viruses, including potato virus Y (PVY), broad bean wilt virus 2 (BBWV2), chilli veinal mottle virus (ChiVMV) and tomato yellow mottle-associated virus (TYMaV). These viruses were detected by RT-PCR with specific primers. Among the three samples, PVY, BBWV2, and ChiVMV were detected in JS1; PVY and ChiVMV were detected in JS3; and only PVY was detected in JS2. However, TYMaV was not detected in three tested samples. The nearly complete PVY-YN-tomatillo genome sequence was determined by overlapping RT-PCR and 3’RACE (Zhang et al., 2020) from the JS2 sample (GenBank accession no.PX092318). BLASTn analysis revealed that PVY-YN-tomatillo shared a nucleotide identity of 94.98% with its closest relative, the PVY-DSMZ isolate (GenBank accession no. OR477269) from Spain. Phylogenetic analysis further confirmed that PVY-YN-tomatillo consistently clustered with strains of the PVYC group, strongly supporting its genetic affiliation within this lineage. The leaf sap (JS2) was mechanically rub-inoculated onto leaves of Nicotiana benthamiana (n=4) and tomatillo (n=6), with two uninoculated plants serving as negative controls. After 14 days, plants inoculated with JS2 sap showed severe leaf deformation and mottling. RT-PCR confirmed PVY infection in all symptomatic plants (10/10), while control plants remained virus free. Typical vein necrosis symptom was also observed on leaves of inoculated tobacco (N. tabacum cv. K326). As the type member of the genus Potyvirus, PVY systemically infects multiple economically important solanaceous crops, including potato, tobacco, tomato, and pepper (Ali., 2024). To our knowledge, this represents the first confirmed report of natural PVY infection in P. philadelphica in Yunnan Province, China. Additionally, molecular detection of both BBWV2 and ChiVMV in tomatillo has been documented (GenBank accession no. PX136837 and PX136838). To date, there have been reports of tomatillo plants infected by other viruses in the United States and Mexico (Kumar et al., 2024). Given the spatial proximity of tomatillo plants to tobacco fields, this weed host may function as a reservoir for PVY. Consequently, the implementation of integrated weed management strategies is essential to effectively reduce viral transmission within tobacco production systems.