title: The question of Citrus viroid IV as a cocadviroid.
abstract: It has been suggested that Citrus viroid IV (CVd-IV) be classified as a species within the genus Cocadviroid. This relationship was based on the presence of a terminal conserved hairpin (TCH) and absence of a terminal conserved region (TCR) as specific structural motifs in common with isolates of Coconut cadang-cadang viroid (CCCVd) as well as phylogenetic relationships with members of the genus Cocadviroid. Evidence is presented for a "vestigial" TCR in CVd-IV as well as the introduction of the terminal repeat region (TRR) motif and an alternative sequence analysis that suggests a closer phylogenetic relationship of CVd-IV to isolates of Citrus exocortis viroid (CEVd), a species within the genus Pospiviroid than to CCCVd. This position is further supported by the striking similarity of biological properties between CVd-IV and CEVd with the suggestion offered that biological evidence be considered for specific adjustments to any overall classification scheme for viroids.
authors.affiliation: Department of Plant Pathology, University of California, Riverside, California 92521-0122, USA. semancik@ucr.edu
authors.forename: J S
authors.initials: JS
authors.lastname: Semancik
authors.forename: G
authors.initials: G
authors.lastname: Vidalakis
mesh_terms: D001483:Base Sequence; D002957:Citrus / Q000821:virology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000821:virology; D010942:Plant Viruses / Q000145:classification / Q000235:genetics; D014772:Viroids / Q000145:classification* / Q000235:genetics