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The genus Dianthovirus consists of three definitive species: carnation ring-spot virus (CRSV) (the type species), red clover necrotic mosaic virus (RCNMV), and sweet clover necrotic mosaic virus (SCNMV) (Francki et al., 1991). A possible fourth species is furcraea necrotic streak virus (FNSV), which is serologically related to RCNMV and hybridizes with cDNA clones to each of the two RCNMV genomic RNA species (Morales et al., 1992). The genus name is derived from Dianthus, the generic name of carnation (D. caryophyllus), which is the most common natural host of CRSV. Dianthovirus particles are isometric, 33 nm in diameter, and sediment as a single species with a sedimentation coefficient (s 20, w) of about 133 S at pH 5.0. They contain a single capsid protein with molecular weight of approximately 37 × 103 and two major genomic RNA species with molecular weights of approximately 1.5 × 106 (RNA-1) and 0.5 × 106 (RNA-2). Dianthovirus particles are stable and easily purified with yields up to 100 mg/kg of infected tissue, and are thus well suited to studies of virus structure and replication. However, di anthoviruses have not been studied as intensively as other plant viruses with bipartite genomes, probably because they do not usually cause serious crop losses. Two comprehensive reviews on the properties of the dianthoviruses have been published within the last few years (Hiruki, 1987; Giesman-Cookmeyer et al., 1995) that attest to recent interest in this genus of plant viruses.