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| Editorial- Bleeding canker of pear - An emerging devastating disease |
| CHEN Gong-you |
| Department of Environment and Resource, School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, P.R.China |
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Abstract Bleeding canker (BC) of pear trees, is a devastating disease in China. The disease was originally observed in Jiangsu Province and its causal agent was identified first as Erwinia sp. in the early 1970’s and latter as a novel species, Dickeya fangzhongdai. BC is epidemically emerging prevalently from April to September annually in pear-growing regions in Zhejiang, Anhui and Shandong provinces, and threatening pear industry currently in China. To better control BC disease, it is crucial to know BC symptomatology, epidemics, etiology, and diagnostics first. The special topic of the three papers have well illustrated the points mentioned above.
The first article by Chen et al. (2020b) described in detail the symptomatology, etiology and epidemiology of BC disease. BC mainly damages pear trunks and branches with no obvious symptoms early and bacterial rusty oozes mixed with tree saps exuded from died tissues later. The diseased portions display small soft and sap-filled brown spots or red streaks with strong smells likely of yeast fermentation. Importantly in this paper, the causal agent is identified as D. fangzhongdai in memory of Prof. Fang Zhongda who was a worldwide distinguished phytopathologist at the Nanjing Agricultural University, China. The pathogen infects not only pear, but also potato, cabbage, tomato and butterfly orchid, and its virulence is stronger than D.?solani on potato, implying the quarantine is necessary.
Since early symptoms of BC are inconspicuous and the isolation of the pathogen from infected trees is time-consuming, the second paper (Tian et al. 2020) developed a TaqMan real-time PCR technique to determine D. fangzhongdai using specific primers basing on an elongation factor G (fusA) gene of the pathogen. Efficiently, 0.2 pg µL–1 DNA and 1×103 CFU mL–1 of the bacterium on asymptomatic trees can be detected by this technique, facilitating early and accurate diagnosis of BC five days before visible symptoms appear.
Species in Dickeya genus are originally separated from Pectobacterium and Brenneria. Some Dickeya speices not only cause diseases in herbal plants, but also exist naturally in lakes or rivers. To distinguish D. fangzhongdai from other Dickeya speices, the third article (Chen et al. 2020a) reported the genome sequences of three isolates of D. fangzhongdai and compared them with other Dickeya genomes available in NCBI database. Phylogenetic analysis showed three D. fangzhongdai strains are clustered in one branch, obviously different from other seven Dickeya speices. Genetic differences are observed in D. fangzhongdai strains in some pathogenicity factors, like type III secretion system (T3SS), T3SS-secreted effector (T3SE), type IV secretion system (T4SS), type IV pili (TFPs), plant cell wall degradation enzymes (PCWDE), and membrane transport proteins, which make the pathogen unique. Interestingly, the TFP deletion makes D. fangzhongdai lose twitching motility and reduce biofilm formation and virulence in pear.
The findings in the papers enrich our knowledge on how epidemic is the BC disease, what is the pathogen, what tools can be used for BC diagnosis, what are pathogenic and phylogenetic differences of the pathogen from other Dickeya species which can be employed for further quarantine detection. Believably, the D. fangzhongdai–pear pathosystem set in the reports provides a platform not only for understanding bacterial pathogenicity in the host, but also for developing new technical tools to control BC disease in agriculture.
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Accepted:
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Cite this article:
CHEN Gong-you.
2020.
Editorial- Bleeding canker of pear - An emerging devastating disease. Journal of Integrative Agriculture, 19(4): 887-888.
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