First report of Tomato spotted wilt virus (Tospovirus, Bunyaviridae) infecting Euphorbia eritrea and Asclepias curassavica in Liguria, Italy

The known natural hosts of tospoviruses, in particular Tomato spotted wilt virus (TSWV), are steadily increasing worldwide. The Liguria region of north west Italy is important for the cultivation of vegetable and ornamental crops, both in open fields and under protection. TSWV and Impatiens necrotic spot virus (INSV) were first reported in Liguria in 1989, when many infected crops were found to be severely affected (Vaira et al., 1993). The virus vector, Frankliniella occidentalis, is present in Liguria on protected crops during the winter and on both protected and field-grown crops during the summer.

In 2000, approximately 20% of a batch of around 10,000 glasshouse-grown pot plants of Euphorbia eritrea L. showed chlorotic and necrotic spots in the stem, starting from the attachment point of true leaves (Figs 1 and 2). TSWV, but not INSV, was detected by both ELISA and immunochromatographic lateral flow assay in tissue showing symptoms but not in tissue without symptoms on the same plants. Only tospovirus particles were detected in symptomatic tissues by electron microscopy. The virus was transmitted mechanically to common herbaceous test plant species, but not to healthy E. eritrea plants. Thus it seems possible that viruliferous thrips fed on, and infected, true leaves and then moved only partly into the stem. Such infected plants were unmarketable.

In 2002, a few potted plants of Asclepias curassavica L. in a glasshouse showed malformation and some necrosis of apical leaves (Figs 3 and 4). Again TSWV, but not INSV, was detected by ELISA and immunochromatographic lateral flow assay, and was transmitted to several herbaceous hosts of TSWV. Electron microscopy of negatively stained sap of affected plants revealed only the presence of tospovirus particles. After removal of necrotic tissues, some plants continued to develop malformation and sometimes necrosis on leaves and stems.

The Asclepiadaceae and Euphorbiaceae include several host of TSWV (Campbell et al., 2003; Peters, 2003), to our knowledge this is the first report of TSWV infection in Euphorbia eritrea and Asclepias curassavica.