A New Immunoassay for Xanthomonas campestris pv. citri and Its Application for Evaluation of Resistance in Citrus Plants. Tsunehiro Kitagawa, Professor, Nagasaki University, Faculty of Pharmaceutical Sciences, Nagasaki 852, Japan. Jian-Guo Hu, Yuhko Ishida, Hiromi Yoshiuchi, Sigematsu Kuhara, Meisatu Koizumi, and Ryoji Matsumoto. Biochemical Scientist, Graduate Students, Nagasaki University, Faculty of Pharmaceutical Sciences, Nagasaki 852, Japan; and Research Plant Pathologists, Kuchinotsu Branch, Fruit Tree Research Station, Kuchinotsu, Nagasaki 859-25, Japan. Plant Dis. 76:708-712. Accepted for publication 21 January 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0708.

A selected antibody enzyme immunoassay (SAEIA) for detection of Xanthomonas campestris pv. citri (cause of citrus bacterial canker) was developed, in which a rabbit antiserum specific for X. c. citri strain QN8201, immobilized cell fragments of X. c. citri strain QN7501, and Β-d-galactosidase–labeled goat anti-rabbit immunoglobulin G were used. The SAEIA was specific for strains of X. c. citri and showed very little cross-reaction with single strains of X. c. pv. pruni and X. c. pv. oryzae, or with several strains of other microorganisms. The detection minimum of the SAEIA was 50 cells per assay for five strains of X. c. citri. SAEIA was used for quantitative comparison of the resistance of 10 kinds of citrus species. Populations of QN7501 in citrus leaves were measured at 1, 4, and 7 days after pinprick inoculation. Leaf homogenate samples did not significantly interfere with this analysis. With resistant citrus species, populations in leaves at 7 days after inoculation were two to eight times lower than those in susceptible citrus.