Cytopathological characteristics of tomato spotted wilt virus isolates

The electron microscopy study revealed that four examined virus isolates in the cells of the infected host plant produced different inclusions depending on the virus isolate and the time of passaging by mechanical transmission. Numerous virus particle inclusions as well as viroplasm and filamentous inclusions typical for TSWV were present in the plant cells infected with TSWV isolate (PPR), This isolate was kept in N. rustica by 4 mechanical transmissions. A similar virus isolate but maintained for 2 years by mechanical transmission in Nicotiana plants (T1) produced virus particle inclusions as well as amorphous inclusions typical for defective isolates. In plant cells infected with the same isolate bur maintained by mechanical transmission one year longer (T2) no virus particle inclusions were produced. In the amorphous inclusions produced by this isolate virus particles were seen, but they were not surrounded by additional membrane. The isolate G induced only amorphous inclusions dispersed within the cytoplasm of infected cells. No virus particles were seen in the amorphous inclusions. The mechanical transmission of TSWV isolates in N. rustica plants reduced the number of virus particles present in the cytoplasm. The defectivenes of the isolate cause also the appearance of a new type of inclusion - the amorphous inclusions.