Bud union crease

Bud union crease is a significant viral disease affecting citrus trees worldwide. It is primarily associated with the presence of the Citrus tristeza virus (CTV), which triggers a physiological incompatibility between the scion and the rootstock. This condition is particularly prevalent in citrus combinations where sensitive rootstocks like sour orange are utilized.

The causative agent is the Citrus tristeza virus, which belongs to the Closteroviridae family. The virus disrupts the vascular tissue, specifically the phloem, causing structural damage at the graft union. This disruption prevents the flow of nutrients and photosynthates, leading to the gradual decline and eventual mortality of the infected citrus tree.

Symptoms of the disease are characterized by a distinct crease or groove forming at the graft union. If the bark is carefully removed, pitting and necrosis are visible in the woody tissue of the rootstock. Externally, the tree displays signs of stunted growth, leaf chlorosis, and general unthriftiness, often resulting in a diminished fruit yield and tree death.

The development and spread of the disease are heavily influenced by the use of infected budwood and the activity of insect vectors. Several factors contribute to the spread:

• Propagation with infected scion or rootstock material.
• Vector transmission by various aphid species, such as Toxoptera citricidus.
• Lack of quarantine measures in citrus nursery operations.

Management strategies for Bud union crease are entirely preventative, as there is no chemical cure for the viral infection. The most effective approach is to utilize certified, virus-free nursery stock. Growers should prioritize planting resistant or tolerant rootstock varieties and implement rigorous pest control programs to manage aphid populations, thereby reducing the risk of transmission in the orchard.