Gibbsiella quercinecans as new pathogen involved in bacterial canker of Russian olive

Russian olive ( Elaeagnus angustifolia ) is an economically important ornamental and crop plant. It has a wide range of biologically active compounds and is regarded as a unique medicinal plant with multiple applications. Members of the order Enterobacteriales isolated from trees are often associated with bacterial canker. During the growing season from 2017 to 2020, forty Gram-negative bacterial strains were isolated from Russian olive trees infected with cankers showing symptoms such as distinctive lesions on the trunk and branches, decline, weakness of trees, cracked bark, depressed brown to black lesions accompanied by exudation of gum, in the Kerman and Mazandaran Provinces of Iran. We used a polyphasic approach to identify and characterize these strains. Using a multilocus sequence analysis approach of four housekeeping loci, namely atpD , rpoB , gyrB , infB , and partial 16S rRNA gene sequences, isolates were identified as Gibbsiella quercinecans . These results were further supported by phenotypic and biochemical tests. Results of the biochemical, physiological and phenotypic experiments, indicated that the isolates are members of the Enterobacteriales and within the genus Gibbsiella . Pathogenicity of the G. quercinecans isolates was confirmed by fulfillment of Koch’s postulates. To our knowledge, this is the first report of G. quercinecans as the causal agent of bacterial canker of Russian olive trees.