Family: Secoviridae

Genus: Waikavirus

Distinguishing features

Waikaviruses have a monopartite genome encapsidated by three capsid proteins; these viruses are transmitted by aphids or leafhoppers. 

Virion

See discussion under family description. 

Genome organisation and replication

The genomic organization of waikaviruses is similar to that of sequiviruses. However, small ORFs have been identified near the 3ʹ-end of the RNA or overlapping with the main polyprotein but in a different reading frame (Figure 3.Secoviridae) (Thole and Hull 1996, Chaouch et al., 2004, Firth and Atkins 2008, Stewart 2011, Stewart 2021). Some experimental evidence has been presented suggesting that subgenomic RNAs are produced from the 3ʹ-region of the RNA (Reddick et al., 1997). The biological significance of the small open reading frames or of the putative subgenomic RNAs is not known. The genomic RNAs are polyadenylated at their 3ʹ-end. The presence of a 5ʹ-linked VPg has not been confirmed experimentally.

Biology

The natural host range of waikaviruses is usually restricted to species within a few plant families (Bockelman et al., 1982). Waikaviruses are not sap-transmitted. Field transmission is in the semi-persistent manner by aphids or leafhoppers. A virus-encoded helper protein is probably needed. Some waikaviruses are helper viruses for the insect transmission of other viruses: Anthriscus yellows virus in the case of parsnip yellow fleck virus (PYFV, genus Sequivirus) (Murant and Gould 1968) and rice tungro spherical virus in the case of rice tungro bacilliform virus (family Caulimoviridae) (this association being responsible for the very damaging rice tungro disease) (Hibino 1983).

Species demarcation criteria

See discussion under family description.