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Contacts:
Scott Adkins
Larry T. Markle
Erin N. Rosskopf
USDA-ARS-USHRL
Fort Pierce, FL 34945
(772)-462-5885
SAdkins@ushrl.ars.usda.gov
Carlye A. Baker
FDACS-DPI
Gainesville, FL 32614
(352)-372-3505 x150
bakerca@doacs.state.fl.us
Symptoms consistent with a virus infection were observed on American black nightshade (Solanum americanum) plants in a vegetable field in southeast Florida in March 2003. A chlorotic mosaic was present on leaves, frequently accompanied by slight distortion (Figs. A, B and C). Symptoms were generally most noticeable on new growth. The presence of a tospovirus was confirmed by symptoms induced on indicator host plants and by inclusion body morphology. Serological tests (ELISA) were used to identify the tospovirus as Tomato spotted wilt virus (TSWV). We believe this is the first report of TSWV infection of American black nightshade in Florida although several other viruses have previously been reported to infect this weed. Since American black nightshade is a common weed in vegetable fields, it can potentially provide a source of TSWV for infection of the crop.
TSWV infects tomatoes, peppers and a wide range of other vegetable, agronomic and ornamental crops in Florida. The Solanaceae and Compositae families contain the largest numbers of susceptible plant species. TSWV is transmitted exclusively by several species of thrips, including the western flower thrips (Frankliniella occidentalis) and the tobacco thrips (F. fusca). Only larval thrips can acquire TSWV, while both the larval and adult thrips can transmit the virus in a persistent, though often sporadic fashion. TSWV replicates in its thrips vectors in addition to its plant hosts. Virus and vector are frequently spread through transport of ornamentals and vegetable transplants.
The extremely wide and overlapping host range of the virus and its thrips vector makes control difficult. A scarcity of host plant resistance genes and a large number of weed and ornamental hosts providing between-crop virus reservoirs exacerbate the situation. The use of virus-free transplants is a necessity. Thrips-proof screens can prevent or delay infection in greenhouse production. Chemical control of the vector is generally not recommended, as it is difficult to achieve good coverage of the thrips and to kill them before they transmit the virus. Scientists at the University of Florida's North Florida Research and Education Center in Quincy have recently developed integrated TSWV management strategies for tomato making use of highly reflective, metalized mulches and Actigard and demonstrated a significant reduction in tomato spotted wilt incidence (http://tmomol.ifas.ufl.edu/TSWMangm.pdf).
Additional information on this virus can be found at:
http://image.fs.uidaho.edu/vide/descr837.htm and http://thrips.ifas.ufl.edu/Background.htm