Isolation and molecular identification of bacterial bark canker in walnut and evaluation of bacteria pathogenicity on the seedling and immature walnuts fruits in Lorestan province

Bacterial canker in walnut is caused by Brenneria nigrifluens. The prevalence of this disease has been increasing in recent years and it is a serious threat to walnut tree in the appropriate conditions. The aim of this study was to isolate and identify the prevalence bacterial walnut canker in Lorestan and to determine their pathogenesis in the raw walnut.

This cross-sectional study was carried out on 105 branches and trunk bark walnut trees suffering of the symptoms of shallow bark canker. After purification and isolation of the disease agents, the bacteria were identified based on phenotypic characteristics. Next, the results were analyze by Ntsys-pc version 2.02 software. The PCR reactions were performed for more accurate identification of the isolates. Overall, five bacterial isolates were selected to study their pathogenesis on the walnut fruits and trunks.

According to the results of phenotypic characteristics of isolates, these strains were classified as B. nigrifluens. Furthermore, based on numerical analysis of the strains with 94% similarity, these isolates were classified into four groups. All isolates produced an expected 255 bp band in the PCR reaction. These strains caused necrotic area on fruit with reddish brown ooze.

The differential phenotypic tests, the pathogenicity test on the raw fruits and specific primers are reliable methods for diagnosis of the etiology of this disease. In our knowledge, the present study is the first report regarding the occurrence of this disease in Lorestan province and also first report of the pathogenicity of B. nigrifluens on fruit in Iran.