Both the small circular RNAs and the double-stranded RNAs associated with the chlorotic rusty spot disease of sweet cherry are also found in sour cherry with similar symptoms

A novel disease, termed cherry chlorotic rusty spot (CCRS) on the basis of its most conspicuous leaf symptoms, has been reported affecting sweet cherry in southern Italy. We have found a series of dsRNAs of a presumably viral origin and two small circular RNAs associated with the CCRS disease. Cloning and sequencing of the most abundant cherry small circular RNA (csc RNA1) has revealed a sequence of 451 nucleotides with hammerhead ribozymes in both polarity strands. This class of ribozyme has been previously found in several viroid and viroid-like satellite RNAs although the association of csc RNAs with the dsRNAs suggests a satellite nature for the former. Recently, we have observed a similar symptomatology in sour cherry trees grown in the vicinity of sweet cherry plants affected by the CCRS disease. Analysis by PAGE of nucleic acids from symptomatic sour cherry tissue has revealed the same pattern of dsRNAs and csc RNAs previously associated in sweet cherry with CCRS disease. Moreover, the presumed csc RNA1 from sour cherry showed strong hybridization with a probe specific for the csc RNA1 from sweet cherry and RT-PCR amplifications using adjacent primers derived from the csc RNA1 from sweet cherry led to a product of the expected length and with essentially the same sequence. Therefore, both the similar symptomatology and the pattern of associated RNAs strongly suggests that a common causal agent is involved in both cases.