Polyphasic characterization of xanthomonads pathogenic to members of the Anacardiaceae and their relatedness to species of Xanthomonas

Abstract

We have used amplified fragment length polymorphism (AFLP), multilocus sequence analysis (MLSA) and DNA-DNA hybridization for genotypic classification of Xanthomonas pathovars associated with the plant family Anacardiaceae. AFLP and MLSA results showed congruent phylogenetic relationships of the pathovar mangiferaeindicae (responsible for mango bacterial canker) with strains of Xanthomonas axonopodis subgroup 9.5. This subgroup includes X. axonopodis pv. citri (synonym Xanthomonas citri). Similarly, the pathovar anacardii, which causes cashew bacterial spot in Brazil, was included in X. axonopodis subgroup 9.6 (synonym Xanthomonas fuscans). Based on the thermal stability of DNA reassociation, consistent with the AFLP and MLSA data, the two pathovars share a level of similarity consistent with their being members of the same species. The recent proposal to elevate X. axonopodis pv. citri to species level as X. citri is supported by our data. Therefore, the causal agents of mango bacterial canker and cashew bacterial spot should be classified as pathovars of X. citri, namely X. citri pv. mangiferaeindicae (pathotype strain CFBP 1716) and X. citri pv. anacardii (pathotype strain CFBP 2913), respectively. Xanthomonas fuscans should be considered to be a later heterotypic synonym of Xanthomonas citri.