Host selection-producing variations in the genome of hop stunt viroid

A random mutant pool of hop stunt viroid (HSVd) was created by shuffling cDNA fragments prepared from three natural HSVd variants obtained from grapevine, citrus, and plum. It was used to infect five host plant species: hop, cucumber, grapevine, peach, and citrus. After infection, progenies having variations characteristic for grapevine and citrus HSVd variants have been preferentially enriched in the homologous plant species, suggesting that strong but different selection pressures affected the genomic RNA when HSVd-infected either grapevine or citrus. In the progeny propagated in cucumber, hop, and peach, variations characteristic to grapevine, citrus, and plum HSVd variants were detected simultaneously as a blend. Accordingly, we showed that at least some of the host-specific variations found in HSVd variants isolated from host plant species, e.g., grapevine and citrus, seemed to have arisen from positive host selection pressures. The HSVd-grapevine variant was found to be ideally adaptable not only to grapevine but to various host plants as well.