Rapid Detection Of Xanthomonas Axonopodis Pv. Citri By Colloidal Gold Immunochromatographic Assay

Bacterial canker of citrus, caused by Xanthomonas axonopodis pv. citri Vauterin (Synonym Xanthomonas campestris pv. citri, Xac), is an important quarantine disease on citrus species and cultivars in many citrus-producing areas worldwide. Wind-driven rain is the primary short-to medium-distance dispersal mechanism for the disease and long-distance transmission normally occurs from the transportation of infected citrus materials or contaminated equipment. Though PCR-based methods and other molecular techniques for diagnosing citrus canker have been described in different published literatures, but because of the molecular complication and the needs of expensive PCR instruments, they may not applicable or available for diagnosing the disease at the entrance ports and other venues of plant quarantine. More applicable and easier detecting technique is required for citrus canker quarantine and for general diagnosis and detection of the disease in citrus orchards. Therefore, the colloidal gold immunochromatographic technique was exploited in the present work to develop new system for citrus canker diagnosis and detection.In the study, the pure antiserum was first obtained from rabbits immunized by several successive injections of cell suspensions of X. axonopodis pv. citri and polyclonal antibody was extracted from the serum using the octane acid and sulphuric acid method. At the same time, the colloidal gold of 30nm for labeling polyclonal antibody of the bacteria was produced through reducing or deoxygenating the gold chloride with trisodium citrate. Then the polyclonal antibody was mixed with the 30nm colloidal gold with a concentration of 20μg/ml to produce gold-labeled polyclonal antibody mixture. After that, a test strip for X. axonopodis pv. citri was assembled with nitrocellulose membrane, the purified antiserum, the gold-labeled polyclonal antibody,...