Identification of Xanthomonas species causing bacterial leaf spot in Australia

Bacterial leaf spot (BLS) is a disease of tomato, chilli and capsicum caused by four species of Xanthomonas. BLS can cause severe crop damage and is a limiting factor of production across the world. The recent taxonomic reclassification of these bacterial species has made it necessary to review the species associated with BLS in Australia. Bacterial isolates associated with disease symptoms have been collected from fields in major production areas of Australia. This collection was supplemented with isolates from NSW and the Queensland herbarium culture collection. These isolates were identified to species using a variety of techniques, including biochemical tests, PCR, MLSA and comparative genomics. At least four species of BLS causing Xanthomonads have been identified in Australia. Comparative genomic studies of 44 sequenced genomes have shown that there is considerable diversity in these pathogen populations. Pathogen race determination and copper tolerance studies will provide functional information about the behaviour of these species and complement the genetic information available. The impact of these species on production and the biosecurity measures required to protect the Australian industry from exotic BLS strains will be discussed