Xanthomonas arboricola pv. fragariae is a doubtful pathovar

The whole genome sequences of two Xanthomonas arboricola pv. fragariae (Xaf) strains with different geographic origin, pathotype strain LMG 19145 and strain LMG 19146, were drafted and compared. The sequence divergence found in their phylogenetic marker genes gyrB, rpoD, dnaK and fyuA suggested that the two Xaf strains were different genomovars of X. arboricola. Moreover, type three secretion system (TTSS) genes were found in the genome of strain LMG 19146, whereas none of these were present in genome of the pathotype strain LMG 19145.
Another ten Xaf culture collection strains were additionally analyzed by 16S rDNA and gyrB sequencing and MALDI-TOF MS. The strains were confirmed as X. arboricola, however, genetically diverse and with different affiliations to the pathotype strains of other X. arboricola pathovars. Specific PCRs for hrcQ and avrBs2 revealed presence of these TTSS genes in only three strains.
Moreover, the Xaf collection strains showed a doubtful pathogenicity in strawberry inoculation tests.
Our sequence based analyses and the unclear pathogenic potential question the criteria that are applied up to now for classifying strains as Xaf but also the validity of Xaf as a separate pathovar of X. arboricola.