Characterization and phylogeny of the novel taxon of Pseudomonas spp., closely related to Pseudomonas avellanae as causal agent of a bacterial leaf blight of cornelian cherry (Cornus mas L.) and Pseudomonas syringae pv. syringae as a new bacterial pathogen of red dogwood (Cornus sanguinea L.)

Abstract

In 2013–2018 on the leaves of Cornus mas L. small brownish spots with regular shape merging also to large necrotic lesions or present as extensive necrotic area from leaf petiole were observed. In 2016 on leaves of Cornus sanguinea L. dark red brownish spots of 4 mm in diameter with necrotic center, were observed. From samples with diseased tissue, fluorescent bacteria were isolated, showing a morphology similar to that of the genus Pseudomonas. The phenotypic characters using LOPAT tests [levan production from sucrose (L), presence of oxidase (O), pectolytic activity on potato (P), the presence of arginine dihydrolase (A), hypersensitivity reaction on tobacco (T)], allowed to classify the isolates to Pseudomonas syringae (LOPAT group Ia). The pathogenicity of isolates was proved on young leaves of Cornus mas and Cornus sanguinea, confirming the ability to infect the species. Detection of genes coding for the phytotoxins coronatine (cfl), syringomycin (syrB and syrD), and yersiniabactin (irp1) showed that none of strains from cornelian cherry nor red dogwood possessed cfl gene, but 5 out of 6 cornelian cherry strains contained the irpl gene. Only the strain 1439, isolated from red dogwood possessed the syrD and syrB genes. Sequence analysis of the 16S rRNA, and housekeeping genes gyrB and rpoB showed that strains from cornelian cherry are most closely related to the hazelnut pathogen Pseudomonas avellane, and that the strain from red dogwood could be identified as Pseudomonas syringae pv. syringae. Further research will determine the exact taxonomic position of the cornelian cherry strains.