Evaluation of the pathogenicity of chrysanthemum stunt viroid variants against dahlia under different conditions

Abstract

AbstractChrysanthemum stunt viroid (CSVd) is an important pathogen that decreases dahlia yields due to stunting symptoms. Here, we evaluated the effect of nucleotide sequence of CSVd, cultivation conditions, inoculum type and infection timing on CSVd‐infected dahlia growth. Inoculation with CSVd after planting resulted in reduced plant height in the second cut flower, but not the first, indicating that the infection may affect the growth of dahlias after approximately 3–5 months. Additionally, there was no significant difference in the degree of symptom severity among the plants infected with the two types of inoculum, synthesized CSVd RNA and CSVd‐infected plant sap. All three CSVd variants affected the growth of dahlias. The reduction in plant height was almost similar among the three variants. However, the reduction in plant fresh weight and compound leaf size in variant JP1 was significantly higher than that in the other variants in the spring experiment. The rates of blown centre in JP1 were also higher than those in the other variants in the spring and winter experiments under the 14.5‐h photoperiod. These results suggest that JP1 is a more severe variant than JP2 and JP3. Dark period interruption improved the reduction in plant height and weight and flower weight, as well as the rate of blown centre in CSVd‐infected dahlias in the winter experiment compared with the 14.5‐h photoperiod. Our results indicate that the three CSVd variants incite stunting symptoms in dahlias and nucleotide sequence of CSVd, photoperiod and infection timing affect the degree of symptom severity.