Viroids, small RNA pathogens capable of infecting flowering plants, coexist in the field with parasitic plants that infest many crops. The ability of viroids to be exchanged between host and parasitic plants and spread in the latter has not yet been investigated. We studied the interaction between the Potato spindle tuber viroid (PSTVd) and Branched bromrape (Orobanche ramosa) using the tomato, Solanum lycopersicon, as a common host. We report the long distance trafficking of PSTVd RNA via the phloem from tomato to O. ramosa, but not vice versa. Furthermore, we identify O. ramosa as a novel host with the ability to facilitate the replication and processing of PSTVd. Finally, molecular variants of PSTVd with single nucleotide substitutions that replicate with different efficiencies in tomato were isolated from O. ramosa.
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