Identification of Reassortment of Orthotospovirus citrullomaculosi in Jiangxi Province, China

Watermelon silver mottle virus (WSMoV) is a thrips-transmitted <i>Orthotospovirus</i> that severely impacts cucurbits production across Asia. Although previous diversity studies focused on the nucleocapsid (<i>N</i>) gene, genome-level evolutionary analyses are lacking. In 2023 and 2024, symptomatic watermelon in Jiangxi Province, China, was analyzed by RT-PCR and high-throughput sequencing, yielding complete genomes of two WSMoV isolates, FZNC and THBC. Multiple-sequence alignment and phylogenetic analysis of the complete sequences of L, M, and S RNAs defined two phylogenetic clades (O and N). However, the Jiangxi isolates clustered in different clades for the L segment versus the M and S segments, suggesting a potential reassortment event. This conclusion was confirmed by RDP4 and RT-PCR analysis, which identified a significant reassortment event involving an L RNA segment derived from a Guangdong isolate (Clade N) and the M and S segments from a Taiwan isolate (Clade O). This study provides the first evidence of natural reassortment in WSMoV, underscoring its potential for rapid evolution. It also constitutes the first report of WSMoV in Jiangxi Province, in East China, marking a concerning expansion of its geographic range into inland China and raising the risk of cucurbit production.