Virulence-related syringomycin gene in grouping of Pseudomonas syringae pv. syringae strains, the causal agent of canker on apricot and almond trees

In recent years, due to the increase in canker symptoms on almond and apricot trees suspected to Pseudomonas syringae pv. syringae (Pss) strains in East Azerbaijan province, detection and determination of some phenotypic characters and genetic characterizations of Pss strains were performed after sampling from 13 different geographical regions. A total of 14 Gram negative and fluorescent producing bacterial strains isolated from apparently diseased samples were identified as Pss based on biochemical and differential LOPAT and GATTa tests. Strains showed slight differentiation in morphological, biochemical and physiological tests. Partial sequences of the rpoD gene confirmed the results of the morphological and phenotypical tests. Pss strains had significant differences in regard to inhibition of Geotrichum candidum mycelial growth by toxin production. A 725-bp fragment of the syrB gene required for synthesisof syringomycin was amplified in all Pss strains. Based on pathogenicity tests on apricot twigs, strains were divided into two groups, one of higher and one of lower virulence. Partial sequences of the syrB gene and constructing a dendrogram using Bayesian inference showed genetic diversity among ten studied strains and divided them into two main groups.This grouping was similar to strains’ grouping based on partial sequences of the rpoD gene.