Characterization of a new citrus viroid species tentatively termed Citrus viroid OS.

A new viroid was obtained from a viroid sample, named 'OS', collected from a citrus plant. The viroid consists of 330-331 nucleotides, contains the central conserved region (CCR) characteristic of the genus Apscaviroid, and has the highest sequence similarity (only 68%) with Citrus III viroid (CVd-III) among known viroids. This viroid, by itself, caused only mild petiole necrosis and characteristically very mild leaf bending in Arizona 861-S1 Etrog citrons (Citrus medica L.), the degree of which differed from that induced by other citrus viroids. This viroid could be a new citrus viroid species belonging to the genus Apscaviroid; for convenience, it was tentatively named Citrus viroid OS (CVd-OS) after the original sample. CVd-OS has chimeric features related to other viroids. In particular, CVd-OS has high sequence similarity with CVd-III and Apple dimple fruit viroid in the putative central and terminal left domains, including a duplicative sequence from the lower CCR of the genus Pospiviroid in the left terminus. Further, CVd-OS shares high sequence similarity with Citrus exocortis viroid (CEVd) in the lower strand of the putative variable and terminal right domains, including the sequence identical to that of the right termini of CEVd and of Citrus IV viroid.