Citrus variegated chlorosis - Xylella fastidiosa

EEffective: August 18, 2010 - December 31, 2011
Resources: Pest Tracker
Screening Aids:
Taxonomic Position: Xanthomonadales : Xanthomonadaceae
Pest Type: Bacteria
Pest Code (NAPIS): FPBFRLB
No manual – See Host Matrix
These Approved Methods are appropriate for:
Pest is vectored by:
Sharpshooter species: Blue-winged sharpshooter (Oncometopia nigricans), present in the United States and Glassywinged Sharpshooter (Homalodisca coagulata). Suspected vectors: Homalodisca insolita, Oncometopia spp., Graphocephala spp., Draeculacephala spp.
Survey
Approved Method(s):
Method Instructions NAPIS Survey Method
Visual Collect leaves of various ages showing typical symptoms; include leaves that show gummy brown lesions on the undersides. Cut green twigs, 6 to 8 inches long from areas of tree that show symptoms. 3031 - General Visual Observation
Signs:
No specific signs are present.
Symptoms:
Early symptoms of citrus variegated chlorosis (CVC) include a foliar interveinal chlorosis resembling zinc deficiency on the upper surface of young leaves as they mature. Small light-brown gummy lesions develop on the lower surface, corresponding with the chlorotic areas on the upper surface. Lesions become dark-brown or even necrotic, enlarging with time. The leaves are often smaller than normal. Very young leaves do not show symptoms.
Key Diagnostics


ID/Diagnostic: Serological

1. Serological: ELISA can detect species, but not strains; requires high concentration of X. fastidiosa (Chang et al., 1993; Hartung et al., 1994). Further confirmation is required. 2. Culture: Culture is made difficult by slow growth rate and uneven distribution within plants (Hartung et al., 1994). Chang et al. (1993) describe how to culture the bacterium on PW, CS20, and PD2 agar medium. Lopes and Torres (2006) discuss BCYE medium and an alternative medium PCYE. 3. Pathogenicity testing: inoculation on susceptible hosts can detect X. fastidiosa.
Mistaken Identities:
Citrus blight, nutritional deficiencies, and viral diseases of citrus can be confused with citrus variegated chlorosis.
In Progress / Literature-based Diagnostics:
Molecular: PCR primers have been developed that detect most, if not all, strains of X. fastidiosa in plant tissues and in the vector, including real-time PCR. Additional primers have been developed that are specific to the strain that causes CVC. These primers are currently being validated (Pooler and Hartung, 1995, and Beretta et al., 1997). Fatmi et al. (2005) developed a BIO-PCR technique to detect X. fastidiosa from grape and citrus. The technique was more sensitive than direct PCR. Multilocus simple sequence repeat markers have been determined to differentiate X. fastiosa strains causing Pierce's disease, CVC, almond leaf scorch, and oleander leaf scorch. (Lin et al., 2005). Wickert et al. (2007) identified SNP (single nucleotide polymorphism) makers that were able to distinguish CVC strains from coffee and citrus for the first time.
Notes:
Xylella fastiosa is on the Select Agent List.
References
  1. Beretta, M.J.G., Barthe, G.A., Ceccardi, T.L., Lee, R.F., and Derrick, K.S. 1997. A survey for strains of Xyllella fastidiosa in citrus affected by citrus variegated chlorosis and citrus blight in Brazil. Plant Dis. 81: 1196-1198.
  2. Bextine, B., and Child, B. 2007. Xylella fastidiosa genotype differentiation by SYBRR green-based QRT-PCR. FEMS Microbiological Letter 276: 48-54.
  3. Bextine, B., Blua, M., Harshman, D., and Miller, T.A. 2005. A SYBR green-based real-time polymerase chain reaction protocol and novel DNA extraction technique to detect Xylella fastidiosa in Homalodisca coagulata. Journal of Economic Entomology 98(3): 667-672.
  4. Chang, C.J., Garnier, M., Zreik, L., Rossetti, V., and Bove, J.M. 1993. Culture and serological detection of xylem-limited bacterium causing citrus variegated chlorosis and its identification as a strain of Xylella fastidiosa. Current Microbiology 27: 137-142.
  5. Ciapina, L.P., Carareto Alves, L.M., and Lemos, E.G.M. 2004. A nested-PCR assay for detection of Xylella fastidiosa in citrus plants and sharpshooter leafhoppers. J. Appl. Microbiol. 96: 546-551.
  6. Fatmi, M., Damsteegt, V.D., and Schaad, N.W. 2005. A combined agar-absorption and BIO-PCR assay for rapid, sensitive detection of Xylella fastidiosa in grape and citrus. Plant Pathology 54: 1-7.
  7. Firrao, G., and Bazzi, G. 1994. Specific identification of Xyllella fastidiosa using the polymerase chain reaction. Phytopathol. Meditterr. 33: 90-92.
  8. Hartung, J.S., Beretta, M.J.G., Brlansky, R., Spisso, J., and Lee, R.F. 1994. Citrus variegated chlorosis bacterium: axenic culture, pathogenicity, and serological relationships with other strains of Xylella fastidiosa. Phytopathology 84: 591-597.
  9. Li., W.-B., Pria Jr., W.D., Lacava, P.M.,Qin, X., and Hartung, J.S. 2003. Presence of Xylella fastidiosa in sweet orange fruit and seeds and its transmission to seedlings. Phytopathology 93: 953-958.
  10. Lin, H., Civerolo, E.L., Hu, R., Barros, S., Francis, M., and Andrew Walker, M. 2005. Mulitlocus simple sequence repeat markers differentiating strains and evaluating genetic diversity of Xylella fastidiosa. Applied and Environmental Microbiology 71(8): 4888-4892.
  11. Lopes, S.A., and Torres, S.C.Z. 2006. An effective and low-cost culture medium for isolation and growth of Xylella fastidiosa from citrus and coffee plants. Current Microbiology 53: 467-469.
  12. Minsavage, G.V., Thompson, C.M., Hopkins, D.L., Leite, R.M.V.B.C, and Stall, R.E. 1994. Development of a polymerase chain reaction protocol for detection of Xylella fastidiosa in plant tissue. Phytopathology 84: 456-461.
  13. Pooler, M.R., and Hartung, J.S. 1995. Specific PCR detection and identification of Xylella fastidiosa strains causing citrus variegated chlorosis. Current Microbiology 31: 377-381.
  14. Wickert, E., Machado, M.A., and Lemos, E.G.M. 2007. Evaluation of the genetic diversity of Xylella fastidiosa strains from citrus and coffee hosts by single-nucleotide polymorphism markers. Phytopathology 97: 1543-1549.