First Report of Chilli Yellow Ringspot Virus Infecting Tomato (Solanum lycopersicum) in China.

Abstract

Tomato (Solanum lycopersicum L.) is a globally important and economically valuable horticultural crop. Chilli yellow ringspot virus (CYRSV), belonging to the genus Orthotospovirus in the family Tospoviridae within the order Bunyavirales, was first reported infecting chilli peppers in Yunnan Province, China, in 2020 (Zheng et al., 2020). Subsequently, it was identified in Hymenocallis littoralis (Jacq.) in 2021. Yunnan Province has a high incidence of orthotospoviral diseases, characterized by diverse viral species and host plants with widespread distribution (Zhang et al., 2021). Three new Orthotospovirus species were initially reported in Yunnan: Tomato zonate spot virus (TZSV) (Dong et al., 2008), Hippeastrum chlorotic ringspot orthotospovirus (HCRV) (Dong et al., 2013), and CYRSV (Zheng et al., 2020). In December 2021, approximately 15 tomato fruits exhibiting symptoms of yellowing, ring spots, wrinkles, and necrosis were observed in a pre-harvest field in Yuanmou City, Yunnan Province, China. The incidence of the aforementioned symptoms in this field is approximately 50%, and the symptoms exhibited by the infected tomato plants are highly conspicuous. Transmission electron microscopy revealed orthotospovirus-like spherical particles approximately 90 nm in diameter. To identify the viral species in these samples, total RNA was extracted from the symptomatic tomato fruits using a Plant Total RNA Extraction Kit (Accurate, Hunan, China). Complementary DNA (cDNA) was synthesized using an M-MLV Reverse Transcription Kit (Accurate, Hunan, China) according to the manufacturer's instructions. PCR amplification was performed using specific primers targeting the N gene of CYRSV (CYRSV-F: 5'-TCACACTTCCAGAGAAGAACTTGGT-3', CYRSV-R: 5'-ATGTCTAACGTTAAGCAACTT-3') under the following conditions: initial denaturation at 98°C for 1 min, followed by 35 cycles of denaturation at 98°C for 10 s, annealing at 56°C for 30 s, extension at 72°C for 1.5 min, and a final extension at 72°C for 10 min. The resulting 828 bp PCR product was cloned into the pMD19-T vector (TakaRa, Japan) for sequencing (GenBank: PV197272.1). Sequence analysis using BLAST revealed that the amplicons exhibited 99.64% nucleotide identity with a CYRSV isolate from H. littoralis in Yunnan, China (GenBank: OP204905.1), and 99.52% identity with a CYRSV isolate from chilli pepper in Yunnan, China (Zheng et al., 2020). To investigate viral presence in CYRSV-infected tomatoes, Nicotiana benthamiana, Nicotiana tabacum K326, and Solanum lycopersicum were utilized as test hosts. Extracts from CYRSV-infected tomato fruits induced yellow ringspot lesions on K326 leaves, dwarfing and leaf curling in N. benthamiana, and yellowing and necrosis in tomato leaves at 9 days post-inoculation. Additionally, RT-PCR assays using specific CYRSV primers detected an 828 bp single specific fragment in all three plant samples. This study represents the first report of natural CYRSV infection in tomatoes. To our knowledge, natural CYRSV infection in tomatoes has not been reported in China. CYRSV causes severe losses in chilli peppers (Zheng et al., 2020; Zhang., et al. 2021). This is the first report of CYRSV infecting tomatoes in Yunnan Province, China. Our results provide a better understanding of the host range of CYRSV and suggest that CYRSV poses a potential threat to tomatoes. Thus, this study provides a foundation for developing effective prevention, control, and quarantine strategies for managing this disease.