Avsunviroidae

Avsunviroidae is a family of viroids characterized by a small, circular, single-stranded RNA genome that does not encode any proteins. These pathogens are unique because their replication occurs specifically within the chloroplasts of the host plant, utilizing the host’s own enzymatic machinery to propagate their infectious RNA molecules.

These viroids have a significant impact on various horticultural crops, most notably avocado, where they cause avocado sunblotch disease, as well as various fruit trees and grapevines. Once established within the vascular system of the plant, the infection becomes systemic, often persisting for the lifetime of the host.

Symptoms of Avsunviroidae infection vary widely but typically include leaf discoloration, yellow or white blotches, necrotic patterns on stems, and severe stunting of fruit growth. In many cases, infected plants show reduced vigor and decreased yields, making the disease economically devastating for commercial fruit production.

Transmission occurs primarily through vegetative propagation, such as grafting with infected scion wood, or mechanical transmission via contaminated cutting tools during pruning. Because they lack a protein capsid, these viroids are highly stable and can easily survive on surfaces of pruning shears or saws if they are not properly sanitized.

Managing Avsunviroidae is challenging due to the lack of chemical treatments against viroid infections. Therefore, effective control relies strictly on phytosanitary practices and preventative management strategies:

• Strict use of certified disease-free propagation material.
• Rigorous disinfection of all pruning tools using approved sanitizing agents.
• Immediate removal and destruction of infected plants to reduce inoculum pressure.
• Implementation of molecular diagnostic testing to detect sub-clinical infections.