Serotypes and particle dimensions of tobacco rattle viruses from Europe and America

Abstract

Five tobacco rattle viruses from Britain and one from The Netherlands were closely related serologically (serotype I), but were only distantly related to one from Brazil (serotype III), which in turn was only distantly related to two from the United States (serotype II). No serological relationship was detected between three tobacco rattle viruses from the United States and one of serotype I, but other workers have found distant relationships between tobacco rattle viruses from the United States and The Netherlands. All ten tobacco rattle viruses examined have straight tubular particles of two or more different lengths, and these lengths are characteristic of the virus isolate. Only the longest particles are infective; these have modal lengths of 188 mμ (serotype I), 195 mμ (serotype II), and 197 mμ (serotype III), and sedimentation coefficients of about 305 S at infinite dilution. The viruses fall into six groups (A–F) on the basis of the modal lengths of their shorter particles, which range from 43 to 114 mμ, but these groups do not correspond to the serotypes. Eight of the viruses retained their characteristic particle lengths unchanged after repeated subculture in the glasshouse, but two, which initially had particle lengths characteristic of group F, changed to lengths of other groups. The main components shown in the diagrams of particle-length distribution were also identified in the analytical ultracentrifuge, showing that they are not artifacts of electron microscopy. The short particles of tobacco rattle viruses seem likely to be specific products of virus-infected cells rather than precursors or fragments of the long particles. The ratio of sedimentation coefficient to particle length is larger for tobacco rattle viruses than for pea early-browning virus, and the particles of tobacco rattle viruses appear about 6% wider in the electron microscope. All these viruses are alike in that the two ends of individual particles differ from one another in shape.