Citrus stubborn disease

Definition

A chronic, systemic plant disease of citrus caused by the wall-less bacterium *Spiroplasma citri* (Mollicutes: Spiroplasmataceae), transmitted by phloem-feeding leafhoppers. The disease produces stunted growth, lopsided fruit with aborted seeds, and twig dieback. In entomological contexts, it exemplifies persistent, propagative transmission: the spiroplasma replicates in the insect vector's hemolymph and salivary glands before being introduced to new host plants during feeding. Principal vectors include *Circulifer tenellus* and *Scaphytopius nitridus* in California and Arizona, and *Circulifer haematoceps* in the Mediterranean region.

Etymology

From the characteristic 'stubborn' persistence of infected trees, which remain unproductive for years without dying.

Example

In California citrus orchards, *Circulifer tenellus* (beet leafhopper) acquires *Spiroplasma citri* while feeding on infected citrus or alternate hosts such as London rocket (*Sisymbrium irio*); the bacterium then multiplies within the leafhopper for 2–3 weeks before the insect can transmit it to healthy citrus trees, a latency period that complicates management programs.

Synonyms

• CSD
• citrus little leaf

Related Terms

• vector-borne disease
• leafhopper
• Circulifer tenellus
• propagative transmission
• phloem
• Mollicutes
• Spiroplasma
• plant disease ecology

Usage Notes

The term is used specifically for the *Spiroplasma citri* disease of citrus; do not confuse with citrus greening (huanglongbing), which is caused by *Candidatus* Liberibacter species and transmitted by psyllids. The plural form is not used; refer to 'cases of citrus stubborn disease' or 'stubborn disease outbreaks' when discussing multiple instances. In entomological literature, emphasis often falls on vector competence and transmission dynamics rather than plant pathology per se.