Citrus greening disease

Definition

A lethal, systemic, graft-transmissible disease of citrus (Rutaceae) caused by fastidious, phloem-limited bacteria of the genus Liberibacter, vectored exclusively by psyllids (Hemiptera: Psyllidae). The Asian citrus psyllid (Diaphorina citri) transmits 'Candidatus Liberibacter asiaticus' in warm regions, while the African citrus psyllid (Trioza erytreae) transmits 'Ca. L. africanus' in cooler, subtropical areas. Infected trees exhibit asymmetrical chlorosis resembling nutrient deficiency ('greening'), stunted growth, and bitter, misshapen fruit; no curative treatment exists, making vector suppression the primary management strategy.

Etymology

From the distinctive yellow-green mottling of leaves in affected trees; also known as huanglongbing (Chinese: 'yellow dragon disease').

Example

In Florida citrus groves, establishment of the Asian citrus psyllid in 1998 and subsequent spread of 'Candidatus Liberibacter asiaticus' collapsed commercial orange production within a decade, demonstrating how a tiny hemipteran vector (~3–4 mm) can drive landscape-scale agricultural devastation.

Synonyms

• huanglongbing
• HLB
• yellow shoot disease

Related Terms

• Vector
• psyllid
• phloem
• fastidious bacterium
• graft transmission
• Integrated Pest Management
• Quarantine
• Asian citrus psyllid
• Liberibacter

Usage Notes

The term is used broadly for the disease syndrome regardless of Liberibacter species or vector; specialists distinguish 'Ca. L. asiaticus' (heat-tolerant, Asian/Americas) from 'Ca. L. africanus' (heat-sensitive, Africa/Mediterranean). 'Greening' refers to the chlorotic symptom, not fruit coloration. The disease is not seed-transmitted and has no resistant citrus cultivars, making it distinct from canker or tristeza.