Integrating Local Lesion Assays with Conventional RT-PCR for Detection of Interspecies Tospovirus Reassortants and Mixed Tospovirus Infections

Tomato spotted wilt virus (TSWV) has historically been the major tospovirus present in North America. Recent emergence of Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV) in Florida and the Caribbean has complicated reliable identification of tospoviruses in this region. Field symptoms of these three tospoviruses are indistinguishable in most host plants, and commercially available TSWV lateral-flow immunoassay reagents cross react with GRSV and TCSV, leading to incorrect diagnoses of GRSV or TCSV as TSWV. Reliable diagnosis of TSWV, GRSV, and TCSV is further confounded by the fact that all currently known isolates of GRSV in the United States are reassortants containing one genomic RNA segment derived from TCSV. To address these practical challenges, we developed and validated genome segment-specific primers for conventional reverse-transcription polymerase chain reaction (RT-PCR) detection of the large, medium, and small RNA segments of TSWV, GRSV, and TCSV. When used in conjunction with local lesion-passaged virus isolates, the genome segment-specific RT-PCR assays developed in this study will facilitate high-throughput screening of plant or thrips samples for interspecies reassortants in epidemiological studies and reliable identification of these three tospoviruses in mixed infections commonly observed in the field.

Emergence of Groundnut ringspot virus and Tomato chlorotic spot virus in Vegetables in Florida and the Southeastern United States

Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV) are two emerging tospoviruses in Florida. In a survey of the southeastern United States, GRSV and TCSV were frequently detected in solanaceous crops and weeds with tospovirus-like symptoms in south Florida, and occurred sympatrically with Tomato spotted wilt virus (TSWV) in tomato and pepper in south Florida. TSWV was the only tospovirus detected in other survey locations, with the exceptions of GRSV from tomato (Solanum lycopersicum) in South Carolina and New York, both of which are first reports. Impatiens (Impatiens walleriana) and lettuce (Lactuca sativa) were the only non-solanaceous GRSV and/or TCSV hosts identified in experimental host range studies. Little genetic diversity was observed in GRSV and TCSV sequences, likely due to the recent introductions of both viruses. All GRSV isolates characterized were reassortants with the TCSV M RNA. In laboratory transmission studies, Frankliniella schultzei was a more efficient vector of GRSV than F. occidentalis. TCSV was acquired more efficiently than GRSV by F. occidentalis but upon acquisition, transmission frequencies were similar. Further spread of GRSV and TCSV in the United States is possible and detection of mixed infections highlights the opportunity for additional reassortment of tospovirus genomic RNAs.