Tomato fruit blotch virus (Blunervirus solani): addition to the EPPO Alert List
Why: Tomato fruit blotch virus (ToFBV - Blunervirus solani) is an emerging virus of tomato. ToFBV was first described from symptomatic tomato samples collected in Lazio (Italy) in 2018 on tomato plants showing fruit dimpling and irregular ripening. However, stored samples collected in 2012 were found to be infected by ToFBV, showing that ToFBV has been present in Italy at least since this date. A distinct isolate of the same virus was also detected in samples from Australia. The complete genome of ToFBV has been sequenced, but until now, Koch’s postulates have not been completed. Following this initial description, ToFBV has been detected in other European countries and other continents, suggesting that it might be already more widespread than originally thought and that it would be necessary to better understand its distribution, biology and epidemiology, as well as its impacts on tomato fruit production. The EPPO Panel on Diagnostics in Virology and Phytoplasmology suggested that ToFBV should be added to the EPPO Alert List.
Where: ToFBV is an emerging virus and its geographical distribution remains uncertain. In particular, records in Canary Islands and Tunisia would need to be confirmed. The NPPO of the Netherlands has intercepted in trade symptomatic tomato fruits originating from the Canary Islands (Spain), but for the moment, the presence of ToFBV has not been confirmed in tomato crops on these islands. Sequences of ToFBV isolates from Tunisia have been deposited in NCBI but were collected from potato (Solanum tuberosum), and there is no indication from other sources that ToFBV can infect potato plants.
EPPO region: Greece (mainland and Kriti), Italy, Portugal, Slovenia, Spain, Switzerland.
South America: Brazil (Distrito Federal).
Oceania: Australia (no further details).
On which plants: symptoms associated with ToFBV have been observed on field and glasshouse tomatoes (Solanum lycopersicum). If confirmed, the detection of ToFBV in potato samples (see above) would enlarge the host range of ToFBV to another economically important crop.
Damage: ToFBV affects tomato fruits, and no leaf symptoms have been reported to date. Affected fruit show irregular and blotchy ripening, dimpling and dark spots. Using transmission electron microscopy (TEM), enveloped and bacilliform virus particles (approximately 25 nm wide × 100 nm long) could be observed in samples prepared from blotched areas of the pericarp of ToFBV-infected tomato fruits. When studying fruit tissues, the highest virus concentration was found in the pericarp. In tomato seeds, ToFBV could be detected on their external tegument, but not in emerging seedlings, thus suggesting that it is not seed transmitted. In some cases ToFBV has been detected with other tomato viruses (e.g. tomato brown rugose fruit virus, pepino mosaic virus, Southern tomato virus). For the moment, the economic impact of ToFBV on tomato production remains unknown.
Transmission: mechanical transmission tests on ToFBV in tomatoes have failed to produce infected plants and no seed transmission could be obtained. Although no vectors are known, it is suspected that the tomato russet mite (Aculops lycopersici) is involved in the disease transmission, as it has often been observed on ToFBV-infected tomato plants. Over long distances, trade of infected plants seems to be the most likely pathway.
Pathways: plants for planting of tomatoes from countries where ToFBV occurs, fruit? viruliferous mite vector(s)?
Possible risks: Tomato is an economically important crop which is grown indoors and/or outdoors across the EPPO region. The emergence of a new virus directly affecting the fruit could potentially represent a serious threat to tomato fruit production. As many aspects of the biology, epidemiology, geographical distribution, host range, and economic impact of ToFBV are unknown, it is difficult to assess the risk it might present to the EPPO region. Nevertheless, it is useful that NPPOs should be made aware of the emergence of this new virus of tomato.
Sources
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