ASBVd

ASBVd, or avocado sunblotch viroid, is a plant pathogenic viroid that infects avocado trees (Persea americana) and causes avocado sunblotch disease. It is classified within the Avsunviroidae family, genus Avsunviroid, and is one of the few viroids known to replicate in chloroplasts. ASBVd is a small, circular, single-stranded RNA that does not encode any proteins. Its replication involves a rolling-circle mechanism in chloroplasts and features hammerhead ribozymes that enable self-cleavage.

Symptoms of avocado sunblotch disease vary with age and cultivar but commonly include foliar mottling or blotching, bark and wood streaks, and surface blemishes or cracking on the fruit. Infected trees may show reduced vigor, irregular bearing, and lower fruit yield and quality. Fruits can be misshapen and display corky or sunken areas on the rind, which reduces market value. The disease can persist in orchards for years, complicating production and quarantine efforts.

Transmission is primarily through propagation material. Infected budwood and grafts are major routes of spread, making certification programs and careful material selection important in nurseries and propagation facilities. Seed transmission is considered rare or uncertain, and there are no well-established insect vectors for ASBVd.

Diagnosis is established through molecular methods, such as RT-PCR and other nucleic acid tests, often using certified diagnostic laboratories. Serological assays exist but molecular approaches are standard for confirmation.

Management centers on prevention and sanitation: using certified virus-free planting stock, removing and replacing infected trees when practical, and implementing quarantine and testing programs to limit spread. There is no cure for ASBVd, so control relies on prevention and careful material movement.