Phenotypic Characterization and Grouping of Pseudomonas syringae pv. syringae Strains, the Causal Agent of Apricot Canker in East Azerbaijan Province Based on Ice Nucleation Activity

Bacterial canker disease of stone fruit trees is one of the most important diseases in the world. In recent years, increasing of stone fruits canker disease symptoms as well as oozing and blast has been observed in some area in East Azerbaijan province of Iran. Fluorescent Pseudomonas syringae pv. syringae (Pss) strains were isolated from apricot trees which showed infected bud, bloom, branch and stem. The isolated strains were characterized based on their morphological, physiological and biochemical properties especially LOPAT and GATTa tests. Host preference was not observed among the tested strains and they showed pathogenicity on apricot green-cut twigs and green been pods with different disease severity. A 725-bp fragment of the syrB gene which is required for synthesis of syringomycin was amplified using specific primers in all strains. The tested strains inhibited the Geotrichum candidum mycelial growth with significant differences by toxin production. Using specific designed INAF/INAR primers, the inaZ gene was partially amplified and different range of ice nucleation activity was detected in all Pss strains. Constructing dendrograms using Bayesian inference showed genetic diversity among strains based on partial sequencing of 16S rRNA, rpoD and inaZ genes. These results showed that there are diversity among the causal agent strains of apricot canker disease based on both pathogenicity, toxin production and ice nucleation activity phenotypes and genetics.