Notes on Family: Pospiviroidae
Viroids are small circular ssRNA molecules, which cause virus-like diseases of plants. There are two families and this one (which is the larger) contains those that have a central conserved region (CCR) and which lack the ability to self-cleave through hammerhead structures. Classification is difficult because nucleotide sequences form its only basis. Recombination between different viroids in mixed infections seems almost certain and adds to the difficulty. An arbitrary level of 90% sequence similarity currently separates variants from species. Comparisons based on the type and sequence of the CCR and phylogenetic trees lead essentially to the same grouping and this has recently made it possible to adopt a more formal classification scheme.
There are no virions.
Circular, ssRNA, consisting of 240-400 nucleotides. No peptides are encoded by the genome.
Genera in the Family