Tomato Spotted Wilt Virus Group*

Tomato spotted wilt virus (TSWV) is the sole member of the group. The particles of this virus are roughly spherical, enveloped, and about 85 nm in diameter. They are quite different from those of any other plant virus, although the structure and cytopathology does resemble that of some members of the Bunyaviridae, a family of viruses infecting vertebrates and also multiplying in their arthropod vectors. Several groups of workers have investigated the structure and composition of TSWV, but there are still some unresolved inconsistencies in the results. This is undoubtedly due to the difficulties of working with a virus that is structurally complex and extremely unstable in vitro. The very characteristic enveloped particles of TSWV, about 85 nm in diameter, are easily identified in thin sections of infected cells, and have always been found inside membranous cisternae in the cytoplasm.