Papaya (Carica papaya) is an important tropical fruit crop, but its production in Taiwan is often constrained by viral diseases, particularly papaya ringspot virus (PRSV) and papaya leaf distortion mosaic virus (PLDMV). In September 2019, papaya plants showing chlorotic spotting symptoms were collected in Pingtung County, southern Taiwan. A distinct virus, designated papaya chlorotic spot-associated virus (PCSaV), was isolated through single-lesion transfers on Chenopodium quinoa. Transmission electron microscopy observed filamentous particles approximately 700 nm in length in infected tissues. High-throughput sequencing and Sanger sequencing revealed a complete genome of 8,075 nucleotides (nts) containing six open reading frames, consistent with the genome organization of carlavirus. The PCSaV genome shared less than 65% nt identity with 71 ICTV-listed carlaviruses, with the highest 64.1% nt identity to cowpea mild mottle virus (CpMMV; HQ184471). Phylogenetic analyses placed PCSaV in the CpMMV clade but as a distinct lineage. The results showed that PCSaV is a new carlavirus. PCSaV reacted with CpMMV antisera, but specific reverse transcription-polymerase chain reaction primers were developed to distinguish the two viruses. Field surveys in Pingtung detected PCSaV in 30 of 176 symptomatic papaya samples (17%), including mixed infections with PRSV, indicating that it represents an emerging viral threat to papaya cultivation in Taiwan. These results demonstrate that PCSaV is a previously uncharacterized carlavirus infecting papaya, and highlight the need for continued surveillance and epidemiological studies to evaluate its impact on papaya production.
Lin et al. (2026) studied this question.