ARS | Publication request: INITIAL SURVEY FOR SPIROPLASMA CITRI, A LEAFHOPPER-TRANSMITTED PATHOGEN INFECTING CITRUS AND OTHER CROPS IN CENTRAL CALIFORNIA.

Submitted to: Entomology Society of America Pacific Branch Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2006
Publication Date: March 4, 2006
Citation: Yokomi, R.K., Mello, A., Kallsen, C., Nunez, J., Gorden, J., O’Connell, N., Freeman, M., Chen, J.C., Fletcher, J. 2006. Initial survey for Spiroplasma citri, a leafhopper-transmitted pathogen infecting citrus and other crops in central California [abstract]. In: Abstracts 90th Annual Meeting Pacific Branch ESA, Maui, Hawaii, March 5-8, 2006. p.108-109.

Technical Abstract: Spiroplasma citri, a phloem-limited, Gram positive prokaryote lacking a true cell wall, is the causal agent of citrus stubborn disease. The vectors of S. citri in California are reported to be leafhoppers (Homoptera: Cicadellidae) and includes the beet leafhopper, Circulifer tenellus, and Scaphytopius spp. The purpose of this research is to survey citrus and other known hosts of S. citri to determine the incidence and distribution of the pathogen and, consequently, its economic impact in California. Initial efforts have focused on assessment and optimization of detection tools and preliminary sampling from different agricultural regions of California. Detection of S. citri was based on isolation and culturing in vitro and examining the cultured microorganism by dark field microscopy. Lyophilized or silica gel-desiccated sample tissue was tested by PCR using spiralin gene primers. PCR detection was reliable when S. citri titer was high but was not reliable during late fall and winter when titer and pathogen distribution were low and erratic. DNA extraction and purification improved PCR detection but made large-scale sample processing laborious and costly. Immunocapture PCR was developed using S. citri polyclonal antiserum. The modified PCR protocol improved detection sensitivity 1,000 to 10,000 fold and will be used in future surveys. Field samples were collected from July to December 2005. S. citri was readily detected in symptomatic citrus trees in Tulare and Kern Counties and was also found in daikon (Fresno Co.) and carrot (Fresno and Kern Counties) showing symptoms for purple top. All cultures of S. citri were preserved and selected isolates are being evaluated for molecular diversity and transmissibility by C. tenellus and Scaphytopius spp. Surveys for S. citri will continue in citrus and other potential hosts in various regions of California in 2006 and 2007.