Cachexia of citrus

Cachexia of citrus is a chronic and economically destructive viroid disease caused by the Hop stunt viroid (HSVd). This pathogen targets the phloem and xylem tissues, causing systemic physiological stress. The disease is characterized by its latent period, which can span several years, allowing the infection to spread undetected within nurseries and production orchards.

The host range of this disease primarily includes various citrus species and hybrids, with mandarins, tangelos, and clementines being particularly susceptible. Transmission occurs primarily through infected budwood used in grafting or via contaminated pruning tools. Because the pathogen is systemic, once a tree is infected, it remains a permanent source of inoculum.

Symptoms of the disease typically manifest near the bud union, although they can spread throughout the trunk and branches. The most diagnostic signs include severe bark cracking, pitting of the underlying wood, and the appearance of gummy, brownish discoloration. These structural changes impede the transport of water and nutrients, resulting in stunting and overall decline of the plant.

The impact of Citrus Cachexia on orchards is significant, leading to reduced canopy growth and substantial yield losses. As the disease progresses, the tree's health deteriorates, making it less productive and commercially unviable. In severe cases, the tree's vascular system becomes so compromised that it eventually dies, necessitating tree removal and orchard replanting.

Prevention is the primary strategy for managing this disease since no cure currently exists. Essential control measures include the use of viroid-tested budwood sourced from certified nurseries and the rigorous sterilization of pruning tools using appropriate chemical disinfectants. If a tree is identified as positive, it must be removed and destroyed to prevent the further spread of the viroid to healthy trees in the vicinity.