CLVd

CLVd, or Citrus leaf viroid, is a plant pathogenic viroid that infects citrus species. Viroids are the smallest infectious agents known, consisting of a short, circular piece of RNA that does not encode proteins and relies on the host plant’s cellular machinery for replication. The CLVd genome is a circular RNA of roughly 335 to 360 nucleotides and, in infected cells, forms compact, rod-like structures. Replication occurs in the host cell nucleus and follows the viroid rolling-circle mechanism typical of members of the viroid family.

Host range and symptoms vary by cultivar and environment. CLVd primarily infects citrus species such as orange, grapefruit, lemon, and lime, and has also been detected in related Rutaceae. Many infections are latent or only mildly symptomatic, but when symptoms appear they can include leaf mottling, distortion, curling, vein clearing, chlorotic flecks, and stunted growth. Yield reductions and poorer fruit quality can occur in some cases, contributing to economic impact.

Transmission is mainly through propagation materials. The viroid is spread when infected budwood or nursery stock is propagated or exchanged, and it can spread within orchards via contaminated pruning tools or grafting practices. There are no known insect vectors for CLVd, and seed transmission is not considered a common route.

Detection and management rely on molecular and culture-based methods. Diagnosis is typically by RT-PCR and sequencing, sometimes complemented by isothermal amplification techniques. Management emphasizes the use of certified disease-free planting material, removal or roguing of infected trees, and sanitation of tools. Meristem tip culture can produce CLVd-free plantlets, and quarantine or regulatory measures are used to prevent spread in commercial nurseries and production systems.