Abstract
Viroids, the smallest RNA pathogen, infect different kinds of horticultural and agricultural crop, and lead to marked quality deterioration in the case of symptomatic infection. It is apparent that their autonomous replication and systemic movement in plants fully depend on the host machinery, since the pathogens lack their own protein-coding genes, whereas how viroids cause disease remains elusive. A model of short interfering RNA (siRNA) derived from viroid RNA that disrupts host gene expression, followed by an abnormal morphological appearance, is more acceptable than those previously proposed. On the other hand, the application of siRNA to block viroid replication is a plausible strategy for the molecular breeding of viroid-resistant plants. Recent advancements in the knowledge of viroid biology, as well as our approach to molecular breeding for Chrysanthemum stunt viroid (CSVd)-resistant chrysanthemum, are briefly reported.
