Identification of the herbaceous host range of Apple scar skin viroid and analysis of its progeny variants

Apple scar skin viroid (ASSVd) is the type member of the genus Apscaviroid of the family Pospiviroidae and is known to cause scarring and dappling of apple fruits. The herbaceous host range of ASSVd was identified using an infectious dimeric clone. Among 13 plant species inoculated with the viroid, nine were found to be systemic hosts and three served as indicator hosts. The viroid could be transferred to these hosts through agroinoculation, rubbing of dimeric RNA transcripts, dimeric DNA plasmids and through sap inoculation. Single-strand confirmation polymorphism (SSCP) analysis of the progeny obtained after inoculation of the infectious ASSVd clone showed the presence of four sequence variants (V1, V2, V3 and V4) which was also confirmed by sequencing. Two sequence variants (V1 and V3) were identified as dominant, representing 47 center dot 72 and 36 center dot 36% of the total progeny, respectively. The V4 sequence variant was similar to the wild type and occurred at a frequency of only 4 center dot 5% of the total progeny.