Impatiens necrotic spot tospovirus on ornamentals in USA: general considerations
In the late 1980s, a significant new virus disease problem began to develop in the glasshouse floriculture industry. Two closely related tospoviruses, tomato spotted wilt tospovirus (TSWV;- EPPO A2 quarantine pest) and impatiens necrotic spot tospovirus (INSV) have been associated with these outbreaks in North American and European glasshouses. This could also be related with the upsurge of Frankliniella occidentalis (EPPO A2 quarantine pest). At least in USA, INSV is currently the more commonly encountered problem in ornamental greenhouses, while TSWV causes more difficulties on outdoor vegetable crops. INSV has a wide host range, and it has caused significant crop losses on many ornamentals, including: cineraria (Senecio cruentus, ranunculus (Ranunculus asiaticus), impatiens (Impatiens wallerana), New Guinea impatiens (Impatiens hybrids), cyclamen (Cyclamen persica), exacum (Exacum affine), begonias, primula (Primula spp. and hybrids), gloxinia (Sinningia speciosa). TSWV has caused problems on chrysanthemum and tuberous dahlia, but has occasionally been detected on other ornamentals. As an example, in the single State of Pennsylvania (US) in 1989-1990, losses caused by INSV and TSWV were estimated of more than 675.000 USD. In addition, some gloxinia growers have experienced 100 % crop loss with INSV infections. Several detection methods for INSV are available like mechanical transmission to Nicotiana benthamiana, and essentially ELISA tests with specific INSV antiserum. Other techniques like direct-tissue blot assay, dot blot immunoassay, direct examination of plant tissue for characteristic viral inclusions are also possible. INSV and TSWV are both transmitted by thrips. Frankliniella intonsa, F. schultzei, F. fusca, F. occidentalis, Thrips palmi, T. setosa and perhaps T. tabaci are vectors of TSWV. For INSV, for the moment F. occidentalis is the only known vector. Seed transmission appears very doubtful for TSWV and has not been investigated for INSV. Therefore, in practice, TSWV and INSV are introduced into the glasshouses by the movement of infected plants and of viruliferous thrips. For these two tospoviruses on glasshouse ornamentals, control methods can include: use of virus-free planting material; monitoring of thrips populations with coloured sticky traps and quick response with adequate means of control to any increase of thrips populations, use of screens (with mesh size ;135 µm) to prevent entry of the thrips into the glasshouse, placing of the new plants in separate compartments of the glasshouse. Research on the production of resistant plants is continuing, and for example transformed chrysanthemum resistant to TSWV are being developed.
Sources
Daughtrey, M.; Jones, R.K.; Moyer, J.W.; Daub, M.E.; Baker, J.R. (1997) Tospoviruses strike the greenhouse industry – INSV has become a major pathogen on flower crops.
Plant Disease, 81(11), 1220-1230.