THE CLOSELY-RELATED CITRUS RINGSPOT AND CITRUS PSOROSIS VIRUSES HAVE PARTICLES OF NOVEL FILAMENTOUS MORPHOLOGY

Some properties of the particles of citrus ringspot virus (CtRSV) and the related citrus psorosis-associated virus (CPsAV) are described. Th e particles of CtRSV have been reported to be sinuous linear structure s about 10 nm in diameter and of two lengths (300 to 500 nm and 1500 t o 2500 nm) representing 'top' and 'bottom' sedimentation components. W e show that these particles are collapsed double-stranded forms of nuc leocapsid-like, highly flexuous open circles formed of filaments 3 to 4 nm in diameter. Top-component filaments had contour lengths of 600 t o 1000 nm, i.e. twice that reported for the corresponding collapsed fo rm. Bottom-component filaments had contour lengths about four times lo nger than those of top-component filaments. The structures suggest tha t CtRSV represents a new genus (possibly family) related to the tenuiv iruses. However, we failed to demonstrate any serological relationship between CtRSV and several tenuiviruses; moreover, the capsid protein sizes and host ranges are quite different. We offer the name Ophioviru s for the proposed new genus.