Identification of the Causal Agent of Bacterial Canker of Stone Fruit Trees Pseudomonas syringae pv. syringae in Kohgiluyeh and Boyer-Ahmad Province and Comparison of Some Cherry Cultivars Resistance to it

Pseudomonas syringae pv. syringae (Pss), the causal agent of bacterial canker of stone fruits, is a dangerous pathogen that attacks more than 200 different plant species. Due to the importance of disease, the purpose of this study was to identify the causal agent of the disease in Kohgiluyeh and Boyerahmad province and comparing the resistance of some cherry cultivars to this pathogen. During 2015-2016, 33 bacterial strains were isolated from stone fruit plants with canker, gummosis, and leaf spot symptoms from different regions of Kohgiluyeh and Boyer-Ahmad province. Isolates were rod-shaped, motile, gram-negative, obligate aerobe, oxidase negative, catalase, levan and tobacco hypersensitive reaction positive, arginine dihydrolase and potato rot negative. The genes responsible for syringomycin synthesis (syrB) and syringomycin secretion (syrD) were detected in all isolates. All strains were able to produce necrosis spots on cherry fruit but showed different virulence. Regarding the phenotypic characteristics, pathogenicity test and PCR results of this study, all isolates were identified as Pss. To study the resistance of cherry plants, Takdaneh Mashhad, Ghaheri and Surati cultivars were selected. There was a significant difference between different cultivars, based on the number of the necrotic lesion on the leaf, length of the necrotic region on the branch and bacterial population in leaf tissue. Among the different cherry cultivars studied in this research, Takdaneh Mashhad cultivar was the most susceptible and Surati cultivar showed the least sensitivity to Pss.