SPECIES AND INFRASPECIES PHYLOGENETIC DISCRIMINATION OF PSEUDOMONAD AND XANTHOMONAD PATHOGENS OF STONE FRUIT AND NUTS
N. Parkinson, J. Elphinstone
Recent phylogenetic analysis of xanthomonad and pseudomonad plant pathogens based on comparison of nucleotide sequences from protein coding loci have proved to reliably classify strains according to coregenome relatedness. Increasingly larger strain populations have been analysed from both pathogen groups, which has defined their diversity in terms of phylogroups, clades and sequevars. The level of discrimination from a single locus is sufficient to facilitate rapid and cost effective identification to species and subspecies level. Analysis of 56 pseudomonad pathogens including all the pathovar reference strains isolated from Prunus, hazel and walnut using the rpoD locus, has placed these pathogens within the phylogenetic structure defined previously using seven loci. The large majority of the strains grouped within phylogroups 1-3. Within Xanthomonas these pathogens are restricted to X. arboricola. The development of sequence reference data-bases to which isolates encountered in the diagnostic laboratory can be compared, will provide opportunities to improve risk assessment, diagnosis, monitoring and surveillance of these important pathogens.