The chrysanthemum stunt viroid (CSVd) is a small, single-stranded, infectious RNA forming a circular secondary structure, which belongs to the Pospiviroidae family and mainly infects certain species and cultivars of Compositae and Solanaceae. The effects on cultivated chrysanthemum are severe, including stunting of plant height, reduced flower size, and flower color bleaching. However, the expression of the symptoms depends on the chrysanthemum cultivars. CSVd is known to be readily transmitted by sap, but the infection rate and incubation period were observed to differ according to the varieties. Some CSVd-resistant cultivars have also been reported and the resistance is heritable in crosses between a CSVd-resistant chrysanthemum cultivar and CSVd-susceptible cultivars.