Molecular Typing and Genetic Characterization of Pathogenic Variants of Xanthomonas axonopodis pv. citri in Taiwan

Molecular typing was applied and optimized for genetic characterization for three pathogenic variants of Xanthomonas axonopodis pv. citri (Xac) from Taiwan. These three novel variants of atypical symptomproducing X. axonopodis pv. citri were designated as Xac-Af, Xac-Ap and Xac-Ar. Based on polymerase chain reaction (PCR) with primers specific to X. axonopodis pv. citri, leucine-responsive regulatory protein (lrp) gene assay and DNA fingerprintings generated by repetitive-sequence PCR (rep-PCR) and amplified fragment length polymorphism (AFLP) were used to compare strains including the three types of atypical symptomproducing strains Xac-Af, Xac-Ap and Xac-Ar, and additional reference strains from pathotypes Xac-A, Xac-A*, Xac-Aw, X. axonopodis pv. auruantifolii and X. axonopodis pv. citrumelo. These three types of X. axonopodis pv. citri variants can be detected with six sets of primer specific for X. axonopodis pv. citri. Cluster analyses by lrp sequence assay, AFLP and combing the band patterns of rep-PCR clearly grouped the atypical symptomproducing variants in types Xac- Af, Xac-Ar and Xac-Ap into the same cluster with typical symptom-producing strains in pathotype Xac-A. These three types of X. axonopodis pv. citri variants could be excluded from strains of Xac-A* and Xac-Aw in these genotypic analyses. Strains of Xac-A* and Xac-Aw were closely related to Xac-A strains in our results. No Taiwan isolate was related to X. axonopodis pv. auruantifolii or X. axonopodis pv. citrumelo. The results further confirmed the atypical symptomproducing variants of X. axonopodis pv. citri in Taiwan belong to pathotype Xac-A.