Immunofluorescence used to distinguish Xanthomonas campestris pathovars on citrus
Gabriel et al. (International Journal of Systematic Bacteriology 39, 14-22) separated, by restriction fragment length polymorphism (RFLP) analysis, the strains of X.c. pv. citri (EPPO Al list) into 3 pathovars X.c. pv. citri (A strains), X.c. pv. aurantifolii (B, C and D strains), X.c. pv. citrumelo (E strains). The EPPO Panel on Bacterial Diseases, in 1990-02, withheld judgement on this reclassification, waiting for the RFLP analysis to be supported by other taxonomic indices. Brlansky et al. (1990) now show that, by use of membrane entrapment immunofluorescence, pv. citri strains all react with a specific antiserum and give no cross reaction with a pooled antiserum to 8 strains of pv. citrumelo; pv. citrumelo strains give no cross reaction with antiserum to pv. citri, but do not all react with the supposed homologous antiserum; pv. aurantifolii strains react with neither antiserum. A few reactions with the mixed antiserum to
pv. citrumelo are found in other pathovars of X. campestris. This immunofluorescence study thus confirms the distinctness of pv. citri and pv. aurantifolii. The bacterial strains causing 'citrus bacterial spot' (pv. citrumelo) appear more heterogeneous, though still distinct from the other pathovars on citrus.
Membrane entrapment immunofluorescence (MEI) is recommended as a useful rapid method which has recently been shown to be sensitive, specific and convenient for processing field samples in citrus bacterial spot epidemics (Gottwald et al., Plant Disease, 72, 781-787).
Brlansky R.H., Lee R.F. & Civerolo E. (1990) Plant Disease 74, 863-868.