Xanthomonas arboricola pv. fragariae : what's in a name?

Polyphasic analysis exposed important heterogeneity between bacterial strains catalogued as X anthomonas arboricola pv. fragariae ( X af) from different culture collections. Two draft whole‐genome sequences revealed pathogenicity related genes of the type‐three secretion system in strain LMG 19146, whereas none were found in the X af pathotype strain LMG 19145. Also, considerable sequence divergence was observed in the phylogenetic marker genes gyr B , rpo D , dna K and fyu A . Further study of 16 X af culture‐collection strains showed that co‐classification is not justified. Partial 16S rRNA gene and gyr B sequencing demonstrated that 12 strains belonged to X . arboricola , but that they did not form one homogeneous group within the species. The four remaining strains were identified as X anthomonas fragariae and X anthomonas sp. All sequence‐based identifications were confirmed by MALDI‐TOF MS fingerprinting. Also, the pathogenicity genes hrc Q and avr B s2 were detected in only three of the 12 analysed X . arboricola strains. The X . arboricola and X anthomonas sp. strains showed pectolytic activity, and upon inoculation in strawberry none of the strains reproduced the leaf blight symptoms reported for X af. This study demonstrates that (i) no clear criteria exist for the identification of strains as X af, (ii) the name X af is currently used for a genetically diverse assortment of strains, and (iii) the species X . arboricola holds many undetermined plant‐associated bacteria besides the described pathovars.