Citrus cachexia

Citrus cachexia is a severe plant disease caused by the Citrus cachexia viroid (CCaVd), which belongs to the genus Cocadviroid. Unlike viruses, this viroid is composed solely of a small, naked circular single-stranded RNA molecule, making it a highly resilient and infectious pathogen that interferes with the host plant's regulatory processes.

The disease primarily impacts specific citrus varieties, including mandarins, tangelos, and kumquats. When these cultivars are grafted onto susceptible rootstocks, they exhibit signs of metabolic failure. The pathogen essentially redirects the plant's resources, causing localized cell damage and disrupting the structural integrity of the tree's vascular tissue.

The biology of CCaVd is characterized by systemic infection, meaning the viroid spreads throughout the entire tree from the point of inoculation. Transmission is primarily man-made: the use of infected budwood during the propagation process is the most common vector. Furthermore, mechanical transmission occurs easily through contaminated pruning tools, as the viroid is quite stable on metal surfaces.

The disease manifests through distinct anatomical changes that can be observed when peeling back the bark of the trunk or scaffold branches. Common symptoms include:

• Deep, vertical pitting or furrows in the wood.
• Brown gumming or necrotic spots at the graft union.
• Stunted tree growth and reduced vigor.
• Significant decline in fruit yield and size.
• Premature branch dieback and eventually tree death.

Control of Citrus cachexia relies heavily on prevention, as there is no chemical cure for infected trees. Growers must strictly utilize certified disease-free nursery stock. Regular sanitation of pruning equipment using high-concentration disinfectants is mandatory. If an infected tree is identified, it must be promptly rogued and destroyed to prevent the pathogen from spreading to healthy neighbors via mechanical contact or shared machinery.