Pathogen Identification And Phylogenetic Analysises Of The "Pear Brown Drippy Disease"

The brown drippy disease of pear was first described in Jiangsu area of China in1970s’, since then, the causal agent has not been reported in any other area. It often caused the tree bleeding cankers in the bark and making the leaves brown spots. The objectives of this study were to identify the pathogen causing this disease of pear and its biological characteristics. The main results as follows:1. There are58strains were isolated from the samples. Biological characteristics were made to the isolated strains in producing pigments、reducing hypersensitive response(HR) in tobacco and colony characteristics.30isolates such as js4、js5、js6and js7were confirmed as the pathogenic bacterias for pathogenicity assay on pear tree, through Koch’s potulates.2. It is important to confirm the phylogenetic analysises of the isolates. In this research,30isolates were made from the diseased stem tissue in order to identify the causal agent from Luniao、Jiangshan and Kaihua. To confirm the morphological identification, the16S and rDNA-ITS region of the isolates was amplified with universal primer. The obtained16S and rDNA-ITS sequences were aligned with GenBank and showed97%(16S) and96%(rDNA-ITS) similarity with30isolates of Dickeya chrysanthemi, and showed99%(16S) and99%(rDNA-ITS) similarity with2isolates isolates of Dickeya pyrifoliae.3. A PCR method was established to detect Erwinia chrysanthemi based on the specific primers designed from the nucleotide sequence of rDNA-ITS gene, which can separate the isolates from other related strains rapidly and correctly.This study facilitates further study on its modes of colonization、protection in pear as well as help to provide a novel way to detect the bacteria for quarantine.