First report of bacterial canker of fig trees caused by Brenneria nigrifluens.
Common fig (Ficus carica) is an important food crop worldwide. A canker disease was observed on common fig trees in the Kerman province, Iran, during 2016-2019. Symptoms included weak trees, brown to black lesions and canker formation on the trunks accompanied by exudation of black sap. A putative pathogen was isolated from infected tissues and characterized using a combination of phenotypic and biochemical tests, pathogenicity assays and molecular tests. On the basis of the colony morphology, biochemical features, molecular data obtained from specific primers and sequence analysis of five genes (16S rRNA, rpoB, gyrB, atpd, and infB), the putative pathogen was identified as Brenneria nigrifluens. Pathogenicity of the bacterial isolates was tested by inoculating one-year-old fig seedlings with a bacterial suspension containing 107 CFU/ml under greenhouse condition. Thirty days after inoculation, no external cankers were observed on inoculated seedlings, but small necrotic lesions appeared on the bark around the inoculation sites, as well as brown necrotic streaks in internal wood. To fulfil Koch's postulates, the pathogen was re-isolated from lesions on inoculated fig seedlings and confirmed as B. nigrifluens. Bacterial canker caused by Pectobacteriaceae members such as Brenneria has led to major economic losses in different trees including walnut, artichoke and Japanese plum around the world. To our knowledge, this is the first report of B. nigrifluens on common fig globally.