Virions are flexuous filaments 690 - 720 x 11 - 15 nm in size. Virion density in CsCl is 1.325 g/cm³ (for Ryegrass mosaic virus, RGMV). Virion S20w is 165 - 166S for most members. Virions contain a single molecule of linear positive sense ssRNA with a 3'-poly(A) terminus. Virion RNA is about 9 - 10 kb in size (Mr 2.7 x 10⁶). Rymoviruses have a single CP with Mr 29.2 x 10³ (RGMV). No lipid or carbohydrate are reported.

The rymoviruses presumably have a genome organization and replication strategy typical of viruses in the family Potyviridae.

Most rymoviruses are moderately immunogenic. No serological relationships among member viruses have been found except for a weak reaction between Oat necrotic mottle virus (ONMV) and WSMV (genus Tritimovirus).

Host Range

Most Rymoviruses have limited but widespread host ranges within the family Graminae but some have relatively narrow host ranges.

Transmission

Transmission by eriophyid mites and mechanical transmission have been reported for most members.

• Genome sequence relatedness.

- CP amino acid sequence identity less than ca. 80%,

- nucleotide sequence identity less than 85% over whole genome,

- different polyprotein cleavage sites.

• Natural host range.

- host range may be related to species but usually not helpful in identifying species. May delineate strains.

• Pathogenicity and cytopathology.

- different inclusion body morphology,

- lack of cross protection,

- seed transmissibility, or lack thereof,

- some aspects of host reaction may be useful (e.g., resistance genes, different responses in key host species).

• Mode of transmission.

- different primary vectors, but vector species not of use in identification to virus species.

• Antigenic properties.

- serological differences.

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