Identification of Melon Severe Mosaic Virus (Orthotospovirus melotessellati) in Cucurbits in Mississippi Highlights the Need for Routine Virus Monitoring with Assays Targeting Multiple Viruses.

Melon severe mosaic virus (MSMV; Orthotospovirus melotessellati) was identified in a pumpkin plant collected in Mississippi during the fall of 2022; the plant exhibited mosaic symptoms, an alligator-skin pattern, and frilly edges on leaves, symptoms typical of cucurbit plants infected with widely prevalent cucurbit-infecting viruses in the United States. High-throughput sequencing was used for virus identification after routine assays for five widely prevalent mosaic-inducing viruses were negative. Screening of stored nucleic acid extracts from 53 additional cucurbit plants collected from Mississippi in 2021 and 2022 using RT-PCR assays revealed two additional positives for MSMV from 2022. MSMV was confirmed in the three positive samples using RT-qPCR and RT-PCR with amplicon sequencing. These results indicate that MSMV was present in the United States at least one year prior to its first report in the country. This example in cucurbits illustrates the importance of seeking diagnoses for plants exhibiting symptoms typical of commonly observed virus diseases as well as the need for routine virus monitoring with diagnostic assays capable of detecting multiple viruses, including exotic viruses. This approach allows for more rapid detection of virus introductions and, with appropriate action, could prevent or limit their establishment and spread in any given location or country.