Fuente: WIPO "tomato" The present disclosure relates to a viral vector suitable for introducing a therapeutic agent, such as a peptide, protein or small RNA, into a host or otherwise treating a host. The vector may include an exogenous RNA segment with a hairpin-like structure or having two or more base-paired regions separated by one or more non-base-paired regions. The exogenous RNA segment may have a secondary structure, minimum free energy, average positional entropy or other attributes within specified ranges, or with values similar to one or more hairpin-like structures of a reference wild type virus. Optionally, the RNA vector may be derived from the reference wild type virus or a relative of the reference wild type virus. In some examples, the vector is capable of capable of systemic and phloem-limited movement and replication within a host plant. In some examples, the reference wild type virus is an umbravirus-like associated RNA.