Additional Ornamental Species as Hosts of Impatiens Necrotic Spot Tospovirus in Italy.

Impatiens necrotic spot (INSV) and tomato spotted wilt (TSWV) tospoviruses are among the most important viral pathogens of glasshouse ornamental plants worldwide (1). Tospovirus infections drastically reduce the market value of plants and create certification problems for international traders. As with TSWV, the number of natural host species recorded for INSV is steadily increasing (2). In 1998, severe INSV infections were found on different ornamental plants in glasshouses in the Piedmont Region of northwestern Italy, together with heavy infestations of the thrips Frankliniella occidentalis. A high proportion of plants were infected with INSV, as shown by enzyme-linked immunosorbent assay (ELISA) with polyclonal antisera and monoclonal antibodies against its nucleocapsid protein. Results were confirmed by sap-inoculation to indicator hosts. Some species were already known to be susceptible to INSV, but others are apparently new hosts (2): Ageratum houstonianum (Asteraceae), showing small necrotic rings and leaf malformation; Cordyline terminalis (Agavaceae), showing chlorotic-necrotic ringspots and leaf malformation; Dianthus chinensis (Caryophyllaceae), showing stunting, mosaic, and leaf malformation (some plants had symptomless infections); Episcia capreata (Gesneriaceae), showing necrotic spots on stems and leaves; Godetia grandiflora (Onagraceae), showing necrotic rings; Maranta leuconeura (Marantaceae), showing chlorotic-necrotic spots and apical malformation; Peperomia obtusifolia (Piperaceae), showing necrotic ringspots and leaf malformations; Scindapsus aureus (Araceae), showing necrotic spots and rings; Torenia fournieri (Scrophulariaceae), showing necrosis on stems and apexes. Thrips feeding damage was high on some species, particularly those showing necrotic ringspot symptoms. It often was difficult to distinguish between true systemic symptoms and local INSV infection at thrips feeding sites. Capsicum sp., Coleus blumei, and Dahlia sp., which also were infected in our study, are species known to be infrequent hosts of INSV (2). References: (1) M. L. Daughtrey et al. Plant Dis. 81:1220, 1997. (2) D. Peters. 1998. Pages 107-110 in: Abstr. 4th Int. Symp. Tospovirus Thrips Floral Vegetable Crops. University of Wageningen, The Netherlands.