Genus Waikavirus

Type Species	Rice tungro spherical virus	(RTSV)

Distinguishing Features

The RNA is longer than 11  kb and has a poly(A) tail. Rice tungro spherical virus (RTSV) and Maize chlorotic dwarf virus (MCDV) RNA contain a small ORF near the 3-end and have about 600 to 700  aa upstream of the structural proteins in the large polyproteins. Aphid or leafhopper transmission is thought to depend on a self-encoded helper protein. The helper protein of some species can assist transmission of other unrelated viruses.

List of Species Demarcation Criteria in the Genus

Isolates belong to distinct species if:

	Gene products differ in amino acid sequence; from limited comparisons values of <70% identity over the entire polyprotein and <80% between NTP-binding domains or proteinase domains or polymerase domains would suggest distinct species (the extent is not possible to define with certainty as too few sequences are to hand),
	They differ serologically; at most, there is a very weak cross-reaction between RTSV and MCDV in immunoblots,
	They differ in host range; RTSV infects rice and some other graminaceous hosts, MCDV infects maize and some other graminaceous hosts, but not rice and AYV infects umbelliferous (dicotyledonous) hosts,
	They are transmitted by different vector species; MCDV and RTSV are transmitted by leafhoppers (Graminella spp. and Nephotettix spp. respectively) and AYV is transmitted by aphids.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, CMI/AAB description numbers ( ), genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Anthriscus yellows virus	(AYV)
Maize chlorotic dwarf virus (194)	(MCDV)
Rice tungro spherical virus (67)	(RTSV)

Tentative Species in the Genus

None reported.

Phylogenetic Relationships within the Family

Not available.

Similarity with Other Taxa

The amino acid sequences in the conserved NTP-binding and RNA polymerase domains of the polyproteins resemble those in the polyproteins encoded by RNA of viruses in the families Comoviridae and Picornaviridae. The number and sizes of the coat proteins (CPs) resemble those of the Picornaviridae although the protein(s) upstream of the CPs is larger than the L protein of aphthoviruses. The properties of the particles and the genomes of these viruses have prompted their description as ‘plant picornaviruses’. Insufficient information is available to make comparisons with picornaviruses or picorna-like viruses that infect insects.

Derivation of Names

Sequi: from Latin sequi, to follow, accompany, attend (in reference to the dependent aphid transmission of PYFV).

Waika: from Japanese, describing the symptoms induced in rice by infection with RTSV alone (i.e., in the absence of Rice tungro bacilliform virus (RTBV)).