Abstract: Polymerase chain reaction (PCR) and newly designed primers, JYF5/JYR5, were tested for selective detection of Xanthomonas axonopodis pv. citri (Xac). The efficiency and reliability of PCR detection method were compared with dot immunobinding assay (DIA) and classical pathogenicity test techniques for detecting Xac in suspensions of pure cells and extracts of citrus samples. Detection limit of PCR was 10 cells or 1.56pg of target DNA per reaction, the sensitivity of PCR assay is higher than DIA (300 cells or more per sample dot). The detection rate of the three techniques (Pathogenicity test, DIA and PCR assay) for Xac reach 100% for symptomatic citrus sample. Differences among the three techniques were clearly evident when using citrus tissues without symptoms, the detection frequency from the least to the most was pathogenicity test, DIA and PCR. Add 15% glycerol in PCR reaction mix can reduce the effect of inhibiting compounds in sample and avoid false negative of PCR.

Key words: Xanthomonas axonopodis pv. citri, PCR, DIA, (dot immunobinding assay), Pathogenicity test