Dickeya fangzhongdai, the causal agent of bleeding canker of pear, is a new member of the Dickeya genus and the only one that infects woody plants.  Recent studies have reclassified several Dickeya isolates as D. fangzhongdai, which were isolated from various environments, including water, Phalaenopsis sp. and Aglaonema sp.  To provide genomic characterization of D. fangzhongdai isolates from pear, the genomes of D. fangzhongdai strain JS5 (=China General Microbiological Culture Collection Center, CGMCC 1.15464T=DSM 101947T), along with two other isolates, LN1 and QZH3, were sequenced and compared to those of other Dickeya spp.  Homology greater than 99% was observed among three D. fangzhongdai strains.  Plasmid, type IV secretion system (T4SS) and type IV pili (TFPs) were found in genomes of D. fangzhongdai isolates.  Comparative analysis of the type III secretion systems (T3SS), type III secretion effectors (T3SE), plant cell wall degradation enzymes (PCWDE) and membrane transport proteins of Dickeya spp. showed some differences which might reflect the variations of virulence, phylogenetic and phenotypic characteristics of Dickeya spp.  In addition, deletion mutant of TFP in D. fangzhongdai JS5 showed no twitching motility and reduced virulence and biofilm formation.  The fingdings of the distinctive plasmid, T4SS and TFPs, as well as the differences of T3SE, PCWDE and membrane transport proteins make D. fangzhongdai isolates unique.  These results also suggested that acquisition of virulence genes by horizontal gene transfer might play some role in the genetic variation of D. fangzhongdai.

 

Bleeding canker, caused by Dickeya fangzhongdai, is a devastating disease of pear in China.  The bacterium causes cankers, branch die-back, and eventually kills pear trees.  The typical sign of bleeding canker infection is a rusty-brown bacterial ooze that exudes down from cankers onto branches or trunks.  However, early symptoms and signs are inconspicuous, which makes effective disease management difficult.  Detection and identification of D. fangzhongdai are time-consuming and difficult because no rapid method exists to date.  In this study, a TaqMan real-time PCR assay was developed for D. fangzhongdai based on an elongation factor G (fusA) gene.  The real-time PCR assay detected 0.2 pg µL^–1 DNA and 1×10³ cfu mL^–1 of D. fangzhongdai.  Based on this assay, bleeding canker on asymptomatic pear trees can be diagnosed as early as 5 days after infection.  The real-time PCR assay can facilitate disease management by providing early and accurate diagnosis of the bleeding canker disease of pear.

 

Fire blight, caused by Erwinia amylovora, is a devastating disease of apples and pears, causing enormous economic losses around the world.  The disease is indigenous to North America and has spread to more than 50 countries since its discovery in 1870s.  Recent reports of the disease in China’s neighboring countries, including South Korea, Kyrgyzstan, and Kazakhstan, pose great threat to the world’s leading producer of apples and pears.  This mini-review intends to provide an update on the disease, pathogen biology, epidemiology, and control.  It will also provide some perspectives and suggestions for the apple and pear industry and growers in China, which will face the imminent threat of this devastating disease.