Study of the morphological characteristics and tracing of the genes involved in rubrifacien pigment production in Brenneria rubrifaciens as the agent of deep bark canker in Walnut

Deep bark canker is a disease which is caused by Brenneria rubrifaciens, and reduces the quality and quantity of Walnut fruits. This study was performed to identify the bacterial agent of deep bark canker based on morphological characteristics, pathogenicity and using specific primers for the genes involved in rubrifacien pigment production.
This cross-sectional- descriptive study was performed on walnut trees with canker symptoms in Lorestan Province. Following purification, bacterial identification was performed using the phenotypic characteristics of the bacterial isolates. Further evaluation of the canker agent was carried out using 2BrIF/2BrIFR and GSP2F/GSP2R primers. Also, the virulence properties of the bacteria were tested on walnut seedling and fruits.
Based on the phenotypic characteristics, 14 isolates were identified as B. rubrifaciens. 671 and 280 bp fragments were amplified in the isolates the during PCR test. In pathogenicity test, symptoms of a rotted and blackened tissue were observed at the site of inoculation. In the phylogenetic analysis, two isolates showed 97% and 98% homology with the bacterial isolates identified in the Genbank.
Comparing other methods, PCR using specific primers is a fast, functional and highly sensitive method to detect B. rubrifaciens. Based on our results on the pathogenicity potential of the strains and the occurrence of the symptoms on walnut seedlings, the pathogen under favorable conditions suffers severe damage to the trees.