Viroids are the simplest RNA-based pathogens known to date.
They consist of 246–401 single-stranded, circular, naked, and non-coding RNAs.
They infect higher plants, induce serious diseases – such as Chrysanthemum chlorotic mottle, Avocado Sunblotch and Potato
Spindle Tuber – and therefore cause considerable economical losses
[1]. It has been shown recently that viroids can replicate in yeast
and thus in other organisms than plants
[2]. Approximately 30 speciesof viroids are currently known and classified into two families: Pospiviroidae and Avsunviroidae.