The curious case of the virus infected tomato fruit

Ben Beale, educator from St. Mary’s County found an odd thing last week. He found in a grower’s high tunnel, tomato fruit that had the symptoms of a virus infection, but there were no foliar symptoms on any of the plants. Some fruit on a cluster had symptoms while other fruit on the same cluster looked perfectly fine. Ben had the fruit tested and got a fast response from Jill Pollok at the University of Delaware Diagnostic Clinic and it was Tomato Spotted Wilt Virus. The cultivar in question Big Beef Plus has TSWV resistance. There could be one or two possibilities for TSWV symptoms showing up in a resistant cultivar and for fruit symptoms but not any foliar symptoms of the virus.

We will look at how tomatoes can get infected by the TSWV (if you already know how this works skip down to the next paragraph). Tomato spotted wilt virus (TSWV) is an obligate parasite, i.e., it must have a living host and must be moved from one plant to another by thrips or through cuttings or possibly seed. This disease can affect tomato and other Solanaceae crops as well as lettuce, beans and cucumber. TSWV may occur in the field but tends to affect greenhouse and high tunnel crops more severely. The virus is transmitted most efficiently by Western flower thrips (WFT) (Frankliniella occidentalis), and less so by Onion thrips (Thrips tabaci), Tobacco thrips (Frankliniella fusca) and several other thrips species. It is not transmitted by Eastern flower thrips (Frankliniella tritici). Only immature thrips can acquire the virus, which they can acquire within 15 minutes of feeding, but adults are just about the only stage able to transmit the virus. Adults can transmit the virus for weeks. It may take 2 – 4 weeks from when the adult thrips first feeds on a plant until initial symptoms are observed. Because of this TSWV appears to worsen in plantings over time.

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