The Plant Viruses, Softcover reprint of the original 1st ed. 1985
Polyhedral Virions with Tripartite Genomes
The Viruses Series

It has been known for a long time that the majority of plant viruses contain RNA and in the past decade and a half it has been realized that many have genomes consisting of three molecules of single-stranded RNA with positive polarity. Among these are viruses belonging to four groups recognized by the International Committee for Virus Taxonomy: the Bromovirus and Cucumovirus groups whose genomes are encapsi­ dated in small icosahedral particles or the Ilarvirus and alfalfa mosaic virus groups with spheroidal or bacilliform particles. In addition to their tripartite genomes, these viruses share a number of other properties and it has been proposed that they should perhaps be grouped in a single virus family for which the name Tricornaviridae has been suggested, the tri indicating the tripartite nature of the genome, the co emphasizing the cooperation of the three genome parts required to initiate infection, and the rna indicating that the genome is composed of RNA. Viruses of this "family" are less uniform in their biological proper­ ties. A number of them are widespread, causing very destructive plant diseases. Viruses such as those of cucumber mosaic and alfalfa mosaic have very extensive host ranges and are responsible for serious crop losses in many parts of the world. Others such as prunus necrotic ringspot or prune dwarf viruses are more restricted in their host ranges but never­ theless infect important perennial hosts such as stone fruits and reduce productivity considerably.

1 The Viruses and Their Taxonomy.- I. Introduction.- II. Members of the Tricornaviridae.- III. Taxonomic Considerations.- IV. Conclusions.- References.- 2 Virus Particle Stability and Structure.- I. Introduction.- II. Atomic Resolution Structures of Spherical Viruses.- III. Virus Descriptions and Structure.- References.- 3 Viral Genome Structure.- I. Introduction.- II. General Structure of Tripartite Genomes.- III. RNA Sequence and Gene Content.- IV. Sequence and Structure of Viral RNAs.- V. Satellite RNAs of the Cucumoviruses.- References.- 4 Virus Multiplication.- I. Introduction.- II. Experimental Systems.- III. Virus Entry and Uncoating.- IV. Virus Replication.- V. Assembly in Relation to Virus Replication.- VI. Cellular Location of RNA Replication.- VII. Cell-to-Cell Spread.- VIII. Conclusions.- References.- 5 Virus Genetics.- I. Introduction.- II. Analysis of Pseudorecombinants Constructed from Genome Parts of Naturally Occurring Virus Strains.- III. Analysis of Incomplete Infections.- IV. Analysis of Mutants.- V. Summary and Prospects.- VI. Glossary of Mutants Cited in This Chapter.- References.- 6 Virus-Host Relationships: Symptomatological and Ultrastructural Aspects.- I. Introduction.- II. Effects of Virus Infection on Host Morphology and Cell Structure.- III. Symptomatology.- IV. Cytopathology.- V. Concluding Remarks.- References.- 7 Serology and Immunochemistry.- I. Introduction.- II. Immunological Techniques.- III. Serological Relationships.- IV. Immunochemical Studies.- V. Taxonomic Implications.- VI. Concluding Remarks.- References.- 8 Virus Transmission.- I. Introduction.- II. Modes of Transmission.- III. Concluding Remarks.- References.- 9 Virus Epidemiology and Control.- I. Introduction.- II. Pollen-Borne Viruses.- III. Aphid-Borne Viruses.- IV. Epidemiology of Bromoviruses.- V. Control.- VI. Discussion.- References.