IDENTIFICATION AND CHARACTERIZATION OF A NEW TOSPOVIRUS ISOLATE FROM ANEMONE CORONARIA L. BY TAS-ELISA AND ELECTRON MICROSCOPY

Anemone coronaria plants with symptoms typical for an infection with tomato spotted wilt virus (TSWV) failed to give positive ELISA results when tested in a triple antibody sandwich ELISA (TAS-ELISA), using an N protein specific monoclonal antibody (MCA) against TSWV, type strain, despite the presence of numerous tospovirus-like particles in leaf sap preparations examined with the electron microscope. The virus isolate was transmitted mechanically to Nicotiana clevelandii and studied further with available polyclonal and monoclonal antibodies as well as electron microscopy.

Further TAS-ELISAs with a TSWV glycoprotein-specific MCA and an N-specific MCA against the Impatients necrotic spot tospovirus (INSV) revealed positive results, indicating a serological relation with TSWV on the glycoprotein and with INSV on the nucleoprotein level. The presence of both viruses as mixture was excluded by westernblot immunoassays, using extracts from infected plants.

Electron microscopy of ultrathin sections cut from infected Nicotiana clevelandii leaf tissue revealed typical arrangements of clusters of spherical particles with 80–100 nm diameter within cisternae of the endoplasmatic reticulum, as well as viroplasms and dense masses that are presumably formed by ribonucleoprotein complexes, and crystalline inclusions that might correspond to the paracrystalline aggregates of fibers formed by the non-structural NS_s proteins described for other tospovirus isolates. According to these cytopathological changes this isolate differs significantly from other INSV isolates that seldom or never form virus particles in infected cells. Two interpretations appear possible for the new isolate: 1. it represents a non-defective form of INSV or 2. it represents a recombinant isolate that has evolved from a mixed infection of INSV and TSWV by exchange of M RNA segments.