The distribution and nucleotide sequences of chrysanthemum stunt viroid in dahlia fields in Japan and the effect of its infection on the growth of dahlias

Chrysanthemum stunt viroid (CSVd) is known to infect a wide range of Dahlia spp ; however, to the best of our knowledge, no detailed study has been conducted on the distribution of CSVd variants, the infection efficacy of sap inoculations, and the symptoms caused by infection of CSVd in dahlias. We have detected CSVd in 94 of 214 dahlia samples, from across eight different Japanese Prefectures, using RT-PCR. Six sequence variants of CSVd were detected from 32 CSVd-infected dahlia samples including 3 variants which have not been previously reported and three previously isolated variants from dahlias or chrysanthemums. Five CSVd variants infected and replicated in both dahlia and chrysanthemum plants by sap and RNA inoculation three months post inoculation. The sequence mutations among those variants did not significantly affect the infection efficacy. Infection of CSVd significantly reduced fresh plant weight, plant height, size of compound leaves, flower diameter, and fresh flower weight of dahlias in two cultivars, though it did not affect the number of nodes. In addition, it altered the color of ray florets and increased the rate at which flowers exposed their disks and that of disk florets. The altered color of ray florets in the ‘Magokoro’ cultivar were darker pink and those of the ‘Portlight pair beauty’ cultivar were darker orange than the uninfected samples. Our results show that CSVd infects a wide range of dahlias in the field and is an important pathogen to manage for their cultivation as it negatively affects their productivity.