Citrus psorosis

Citrus psorosis is a destructive viral disease caused by the Citrus psorosis virus (CPsV), which belongs to the genus Ophiovirus. It is a systemic pathogen affecting various citrus species, including oranges, grapefruits, and mandarins. Because the virus spreads throughout the plant's vascular system, an infected tree remains a reservoir for the virus for the remainder of its lifespan.

The disease is characterized by distinct symptoms on the bark, primarily the scaling of the bark on trunks and main branches. These lesions often resemble flakes, giving the disease its name. Foliar symptoms, such as chlorotic flecking or patterns in young leaves, may appear periodically. Over time, the disease leads to a gradual decline in tree vigor, reduced fruit size, and significant yield losses, eventually resulting in tree death.

The biology of the virus involves a prolonged latent period where the tree may show no visible symptoms for years. Transmission is primarily vegetative. In commercial settings, the most significant transmission route is the use of infected budwood during grafting. Transmission by insect vectors is not considered a primary concern for this specific virus, making the movement of nursery stock the critical factor in its spread.

Development and spread of the virus are heavily influenced by orchard management practices. Environmental conditions do not trigger the virus itself, but the physiological stress of the tree may influence the expression of bark symptoms. The virus spreads across regions and continents through global trade of citrus budwood and nursery plants, highlighting the need for strict quarantine measures.

There is no known cure for infected trees, making preventive strategies the only effective approach. Control programs must focus on the following:

• Establishing strict clean-stock certification programs for nurseries.
• Utilizing thermotherapy or tissue culture techniques to produce virus-free foundation plants.
• Sanitizing pruning tools thoroughly between trees to prevent mechanical transmission.
• Systematic monitoring and immediate removal of symptomatic trees to protect the remaining orchard.