Xanthomonas hydrangeae sp. nov., a novel plant pathogen isolated from Hydrangea arborescens .

This paper describes a novel species isolated in 2011 and 2012 from nursery-grown Hydrangea arborescens cultivars in Flanders, Belgium. After 4 days at 28 °C, the strains yielded yellow, round, convex and mucoid colonies. Pathogenicity of the strains was confirmed on its isolation host, as well as on Hydrangea quercifolia . Analysis using MALDI-TOF MS identified the Hydrangea strains as belonging to the genus Xanthomonas but excluded them from the species Xanthomonas hortorum . A phylogenetic tree based on gyrB confirmed the close relation to X. hortorum . Three fatty acids were dominant in the Hydrangea isolates: anteiso-C 15 : 0 , iso-C 15 : 0 and summed feature 3 (C 16 : 1  ω 7 c /C 16 : 1  ω 6 c ). Unlike X. hortorum pathovars, the Hydrangea strains were unable to grow in the presence of lithium chloride and could only weakly utilize d-fructose-6-PO 4 and glucuronamide. Phylogenetic characterization based on multilocus sequence analysis and phylogenomic characterization revealed that the strains are close to, yet distinct from, X. hortorum . The genome sequences of the strains had average nucleotide identity values ranging from 94.35-95.19 % and in silico DNA-DNA hybridization values ranging from 55.70 to 59.40 % to genomes of the X. hortorum pathovars. A genomics-based loop-mediated isothermal amplification assay was developed which was specific to the Hydrangea strains for its early detection. A novel species, Xanthomonas hydrangea e sp. nov., is proposed with strain LMG 31884 T (=CCOS 1956 T ) as the type strain.