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
No specific signs are present.
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.
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.
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.