Occurrence of Tomato spotted wilt virus in Stevia rebaudiana and Solanum tuberosum in Northern Greece

Tomato spotted wilt virus (TSWV) (genus Tospovirus, family Bunyaviridae) was first reported in Greece during 1972 (3) and currently is widespread in the central and northern part of the country infecting several cultivated and wild plant species (1,2). In June 2006, virus-like symptoms similar to those caused by TSWV were observed on sweet honey leaf (Stevia rebaudiana (Bertoni) Bertoni, [synonym Eupatorium rebaudianum Bertoni], family Asteraceae) plants in an experimental field in the prefecture of Kilkis and on potato (Solanum tuberosum, family Solanaceae) plants growing close to tobacco in the prefecture of Kozani in northern Greece. Diseased S. rebaudiana plants expressed chlorotic and necrotic rings and line patterns on systemically infected leaves and occasionally a general chlorosis or dwarfing of the plant. Potato plants expressed only necrotic rings or lesions and a mild plant dwarfing. Seven percent of the S. rebaudiana plants, but only 0.1% of the potato plants, were showing symptoms. TSWV was detected by ELISA using polyclonal antisera in all symptomatic plants of both species, but those plants tested negative for Potato Y virus (PVY), Cucumber mosaic virus (CMV), Alfalfa mosaic virus (AMV), and Potato leafroll virus (PLRV); all viruses known to occur in these areas. Sap from symptomatic plants was used to mechanically inoculate Petunia × hybrida cv. Blue magic, Nicotiana tabacum cvs. Samsun NN and Basmas, N. benthamiana, N. glutinosa, N. rustica, Datura stramonium, and Physalis floridana. Sap from both S. rebaudiana and potato produced typical symptoms of TSWV on the diagnostic test plants; all Nicotiana species and cultivars, as well as D. stramonium and P. floridana, reacted with chlorotic and necrotic lesions on the inoculated leaves followed by systemic mosaic and mottling of the leaves. None of the isolates produced systemic infection on P. × hybrida. Adult thrips, identified as Thrips tabaci, were collected from infected plants of both hosts in the field and determined to be infected with TSWV by the petunia leaf disc method (4). Symptoms observed in the field on both hosts where reproduced in the laboratory after infestation of healthy plants with TSWV-infected individuals from a tobacco population of T. tabaci. To our knowledge, this is the first official report of a TSWV infection in S. rebaudiana. Potato is a known host for TSWV, however, to our knowledge, this is the first natural infection detected in Greece.