Previously, we have produced a phylogeny of species type strains from the plant-pathogenic genus based on sequences. To evaluate this locus further for species and infraspecies identification, we sequenced an additional 203 strains comprising all the pathovar reference strains (which have defined plant hosts), 67 poorly characterized pathovars, currently classified as , and 59 unidentified xanthomonads. The well-characterized pathovars grouped either in clades containing their respective species type strain or in clades containing species related to . The , and species complex, and were discriminated as -related clades and comprised a large proportion of unidentified strains as well as 80 pathovars representing all the pathovars and many poorly characterized pathovars, greatly increasing the plant host ranges of the constituent species. Most xanthomonads from these three large clades were isolated from a taxonomically diverse range of plant hosts, including many weed species, from field systems in India, suggesting that these lineages became established and diversified in agricultural areas in this region. The majority of these xanthomonads had minimal sequence diversity, consistent with rapid and highly extensive pathovar diversification that has occurred in relatively recent times. Low-intensity farming practices may have provided conditions conducive to pathovar development, and evidence for pathovar diversification within other regional angiosperm floras is discussed. The locus was sufficiently discriminating to identify diversity within many species. Seven branches or clades were sufficiently distinct to be considered as potential novel species. This study has provided a comprehensive xanthomonad classification framework and has firmly established sequencing as a rapid and efficient identification tool.


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GenBank accession numbers of sequences determined in this study. [PDF](27 KB)


Comprehensive xanthomonad phylogeny, presented as a conventional phylogenetic tree. [PDF](607 KB) [NB. This figure is large and, if a printout is required, A3 paper should be used in order for the text to be legible]

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