Abstract
Chrysanthemum stunt viroid (CSVd) is one of the problematic pathogens known to infect chrysanthemum (Dendranthema grandiflorum) plants and causes various symptoms, such as a reduction in plant height, which is a serious problem in cut flower production. No natural sources with resistance to CSVd have been reported. By quantifying the CSVd titer within the plant, we identified the cultivar ‘Utage’ as a plant in which the increase of the CSVd titer was slowest among 6 cultivars tested. ‘Utage’ self-pollinated, and 67 resulting seedlings were screened for CSVd resistance using reverse transcription polymerase chain reaction (RT-PCR), nested-PCR, micro-tissue (MT) direct RT-PCR, and real-time RT-PCR. Of these 67 seedlings, 9 plants lacked the obvious CSVd band detected by RT-PCR. Five months after grafting to CSVd-infected plants, the CSVd titers of 3 plants (C7, A30, and A27) were about 1/240, 1/41000, and 1/125000 compared to that of ‘Utage’, respectively. These 3 plants were comfirmed to have strong resistance to CSVd. In C7, local distribution of CSVd was observed in the youngest expanded leaf by micro-tissue direct RT-PCR and in situ hybridization. For A30 and A27, CSVd was hardly detected in the whole plant. These 3 plants will contribute to the elucidation of CSVd resistance mechanisms.
