Isolation and Characterization of Brenneria nigrifluens Causing Bacterial Shallow Bark Canker of Walnut Trees in Golestan Province, Iran

Shallow bark canker incited by Brenneria nigrifluens is considered one of the most dangerous diseases which can cause a significant reduction in walnut and timber production.  During spring and summer of 2019, walnut gardens were surveyed for symptoms like leaf spot, fruit, and stem canker from four different regions of Golestan province located in Iran. A set of 11 Gram-negative bacteria were isolated from sample tissues with symptoms. In pathogenicity tests on unripe walnut fruits, all isolates caused typical black necrotic lesions covering almost the entire pericarp. Results of selected phenotypic tests and whole-cell protein patterns indicated that all isolates were the same as described for the type strain of B. nigrifluens. Phylogenetic analysis based on sequencing of the gyrB, rec A, and 16s rRNA genes of the representative isolate formed a unique clade, well-characterized, and separated from related species. The results of this study can have a bearing on the choice of disease management strategies.