Susceptibility of cherries to bacterial canker (Pseudomonas syringae pv. syringae) in field and laboratory.

Bacterial canker caused by Pseudomonas syringae pv. syringae is an important disease in cherries worldwide but low attention has been paid to breeding and selection of cherries for bacterial canker resistance. In this research, 21 selected Iranian and 7 introduced cultivars of sweet/sour/ducke cherries were examined for resistance to bacterial canker by artificial inoculation in field and laboratory condition. Correlation between canker resistance with wood diameter was also examined. Three local P. syringae strains were studied using LOPAT and GATTa tests and used as inoculum. For laboratory test, two-years-old dormant shoots were used and the canker length measured one month after inoculation. For field assay, trunk and shoots of two-years-old plants were inoculated in late autumn and eight months later, lesion length was measured. Based on result, in excised shoots, lesion length was the lowest in Shamloo and the highest in KB25. In both organs tested in field condition, Siyah-daneshkadeh was the most susceptible and Albaloo-meshkinshahr the most resistant. Cluster analysis grouped the cultivars in three relative susceptibility groups including highly susceptible, susceptible and intermediate constituting 3.6%, 70.7%, and 25% of the material, respectively. No correlation was found between field and laboratory data but canker length in tree organs correlated together. Lesions were collectively larger in trunk than shoot and a direct correlation existed between shoot diameter and necrosis length. In conclusion, cherries vary in susceptibility to P. s. pv. syringae and artificial inoculation in orchard condition is the recommended method for cultivar discrimination.