Genetic variability of Iranian strains of Pseudomonas syringae pv. syringae causing bacterial canker disease of stone fruits

Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from healthy and diseased stone fruits tissues sampled from 38 stone fruits orchard sites in Iran in 2010 and 2011. These strains were tested for pathogenicity and the presence of the syrB gene and were genetically characterized by using ERIC (enterobacterial repetitive intergenic consensus), REP (repetitive extragenic palindromes), and BOXAIR and IS50 (insertion sequences) primers and PCR. All 78 strains of Pss tested were moderately to highly pathogenic on Loring peach seedlings. A total of 78 isolates of the Pss amplified a 752-bp fragment with the syrB primers. To assess genetic diversity among the strains, genomic DNA was extracted from strains and used in rep-PCR and IS50-PCR analysis. Cluster analysis was performed using UPGMA. The strains of Pss were separated into nine distinguishable genotypic groups by the combination data set of both rep-PCR and IS50-PCR at 73 % similarity level. There was no significant correlation between genetic diversity and geographical origin of the isolates. These results indicate that a combination of rep-PCR and IS50-PCR fingerprinting can be used as a high resolution genomic fingerprinting method for elucidating intrapathovar diversity among strains of Pss. The results of this study demonstrated the existence of a considerable genetic diversity among Pss strains causing canker of stone fruit trees in Iran. In this study, genetic variability in Iranian strains of Pss were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.