GENOTYPIC CLASSIFICATION OF ATYPICAL SYMPTOM-INDUCING XANTHOMONAS AXONOPODIS pv. CITRI STRAINS IN TAIWAN

Citrus canker caused by Xanthomonas axonopodis pv. citri (Xac) is one of the most important diseases in many citrus-producing countries. This disease is characterized by the formation of erumpent, callus-like lesions with a water-soaked margin. Several distinct phenotypes of Xac have been reported internationally. Three novel atypical symptom-inducing strains, designated Xac-A super(f), -A super(r) and -A super(p) were reported recently from Taiwan (Lin et al., 2005, 2008). In this study, DNA fingerprintings generated by REP-PCR and amplified fragment length polymorphism (AFLP) (Ah-You et al., 2007) were optimized to compare 36 strains, including the atypical symptom-inducing strains Xac-A, -A super(p) and -A super(r) from Taiwan, and the additional reference strains Xac-A, -A*, -A super(w), X. axonopodis pv. aurantifolii and X. axonopodis pv. citrumelo. Cluster analysis by combining the band patterns of ERIC-and REP-PCR clearly grouped the atypical symptom-inducing strains in types Xac- A super(f), -A super(r) and -A super(p) into the same cluster with typical symptom-inducing strains in type Xac-A. These three types of atypical symptom-inducing Xac strains could be excluded from strains of Xac-A* and -A super(w) in this combined analysis. Based on AFLP analysis, all type Xac- A super(f), -A super(r) and -A super(p) strains were also grouped into the same cluster with strains in type Xac-A. Strains of Xac-A* and -A super(w) were closely related to Xac-A strains in our results. No Taiwan isolate was related to X. axonopodis pv. aurantifolii or X. axonopodis pv. citrumelo. The results further confirm the atypical symptom-inducing Xac strains in Taiwan belong to the A type of Xac.