Identification and genotypic characteristics of Erwinia amylovora isolates, the causal agents of fire blight on pome fruit trees in Hamadan province

One of the most destructive diseases of pome fruit species which causes irreparable damage to gardening products worldwide is fire blight disease caused by Erwinia amylovora. In Iran, it was first observed in pear trees in Alborz province and then spread across fruit orchards in the country. One of the main problems in fire blight management is evaluating causal agent genotypic characteristics. Thus, the present research was conducted to characterize genotypic features of E. amylovora as the cause of fire blight disease in pome fruit species in Hamadan province, Iran.

In this study, the samples with symptoms of canker on shoots and blight blossoms were observed and collected from the orchards in Hamadan province located in the west of Iran. After isolation, the isolates were purified for further studies. Phenotypic, biochemical, and pathogenicity tests were performed due to standard bacterial criteria. Phenotypic and biochemical tests of strains were examined by Ntsys-pc 2.02 software. A total of 15 representative isolates were selected and analyzed due to the size of amplified DNA using primers Ea71 and genetic features of the rep-PCR test using primers ERIC and BOX. For more accuracy and higher reliability of the specific primers results, the 16S rDNA_ gene of two representative isolates was amplified and subjected to sequencing.

Based on the biochemical, pathogenicity and molecular tests, a total of 34 isolates were identified as E. amylovora. Due to the numerical analysis, the data obtained by phenotypic and biochemical tests were similar at 89% level. Therefore, the isolates obtained from a specific host or region was grouped very close to each other. In the PCR tests survey, the isolates amplified 187 base pair expected fragments. The results of determining sequences indicated that both isolates were similar to E. amylovora showing 97% identity to the type of strains in the NCBI database. Due to data from the rep-PCR analysis, the isolates were divided into three groups at the similarity level of 77%.

The results of genetic diversity using rep-PCR showed that there is no significant difference among E. amylovora bacterial isolates from different regions of Hamadan Province. Moreover, they showed high similarity to each other and placed close to each other. Our results confirm other studies regarding phenotypic characteristics of E. amylovora. Our results confirm that the isolates are homogenous in Hamadan province of Iran. To summary, these findings can be applied to breeding programs to better management of the bacterial disease.