Citrus Stubborn Disease
CSD is caused by Spiroplasma citri, a phloem-limited, cell-wall-less bacterium. S. citri is transmitted in a propagative, circulative manner by several leafhoppers including Circulifer tenellus and Scaphytopius nitridus in citrus-growing regions of California and Arizona and C. haematoceps (syn. Neoaliturus haematoceps) in the Mediterranean region. The pathogen multiplies in the vector but no transovarial transmission occurs. Spatial and temporal analysis of CSD incidence indicate only primary spread occurring and no or very limited secondary spread (citrus to citrus). Scaphytopius can develop on citrus but the population remains low to negligible throughout the season. C. tenellus and C. haematoceps have a wide host range which includes many natural hosts of S. citri but citrus is a non host of these leafhoppers. Citrus becomes infected when inoculative Circulifer vectors feed temporarily on citrus during migratory flights.
S. citri is graft-transmissible with side grafts but rate of bud transmission is very low due to low pathogen titer. Seed transmission does not occur. S. citri is phloem-restricted where it multiplies and moves slowly through the tree. CSD has a long latent period of months to years after inoculation. Detection varies with season with highest titer being in hot summer months, concomitant with most pronounced symptom expression.
Other Common Names
Little-leaf disease (Israel); safargali (Egypt); early descriptions in California include pink nose, acorn fruit, blue albedo and crazy top in Arizona.
Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]