Detection of Xanthomonas axonopodis pv. citri on Citrus Fruits Using Enzyme-Linked Immunosorbent Assay

  • Published : 2001.02.01

Abstract

Detection of Xanthomonas axonopodis pv. citri (Xac) on citrus fruits for exporting is usually made by bacteriophage test (BPT) to demonstrate the pathogen-free status. BPT has rather time-consuming and complicate procedures for dealing with massive samples to be inspected. In this study, enzyme-linked immunosorbent assay (ELISA) was applied to detect Xac on fruits, and compared with BPT. In ELISA, positive reactions occurred in the bacterial densities of $3\times10^5$ cells/ml or more. To detect the bacterial infection on citrus fruits with a density of lower than $3\times10^5$ cells/ml, the bacterial suspensions were mixed with fruit rinse water and incubated in broth medium. Ordinary peptone sucrose broth (PSB) was not a proper medium for increasing Xac density specifically enough to be detect by ELISA. On the other hand, modified PSB (MPSP) amended with Fe-EDTA (0.25 g/$\ell$) and 2.5% potato-dextrose broth sufficed to differentiate uninfected and infected citrus fruits by ELISA after 24 h incubation of the fruit rinse water. Using various citrus samples from infected and uninfected fields, efficiencies in detecting Xac on fruits were compared between ELISA and BPT. For infected fruits samples, ELISA detected Xac by 100%, while BPT by about 44%, indicating that the detection efficiency was improved by 23.5% by ELISA, compared to BPT. In addition, ELISA has simpler procedures for testing and is less time-consuming than BPT, suggesting that ELISA may be accurate and simple method to detect Xac on citrus fruits.

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