First Report of Pectobacterium aroidearum Causing Soft Rot of Chinese Cabbage in China

Abstract

HomePlant DiseaseVol. 102, No. 3First Report of Pectobacterium aroidearum Causing Soft Rot of Chinese Cabbage in China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Pectobacterium aroidearum Causing Soft Rot of Chinese Cabbage in ChinaH. Xie, X. Y. Li, Y. L. Ma, and Y. TianH. Xie†Corresponding author: H. Xie; E-mail: E-mail Address: xiehua@baafs.net.cnSearch for more papers by this author, X. Y. LiSearch for more papers by this author, Y. L. MaSearch for more papers by this author, and Y. TianSearch for more papers by this authorAffiliationsAuthors and Affiliations H. Xie † X. Y. Li Y. L. Ma Y. Tian , Beijing Agro-Biotechnology Research Center, Beijing Academy of Agriculture and Forestry Sciences, and Beijing Key Laboratory of Agricultural Genetic Resources and Biotechnology, Beijing 100097, P. R. China. Published Online:19 Jan 2018https://doi.org/10.1094/PDIS-07-17-1059-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In June to October 2015, we surveyed Chinese cabbage (Brassica rapa subsp. pekinensis) exhibiting soft rot symptoms in a commercial field in Beijing, China. The lesions initiated at the petiole base, expanded, and rapidly covered the entire plant. Analysis of 30 isolates from infected plants revealed that one of them, KC20, was an isolate of Pectobacterium aroidearum, whereas the other 29 isolates were the common Chinese cabbage pathogen P. carotovorum. Bacterial strain KC20 was tested for pathogenicity by dropping a bacterial suspension (10 μl/inoculation site, 2 × 108 CFU/ml) onto sterilized Chinese cabbage petiole surfaces with sterile distilled water as a control. Water-soaked lesions appeared on inoculated petioles in 24 h after incubation in a growth chamber at 28°C, and strains were reisolated successfully from symptomatic Chinese cabbages to complete Koch’s postulates. In a PCR assay, strain KC20 produced a 434-bp product with pel gene-specific primers Y1/Y2 for Pectobacterium spp. (Darrasse et al. 1994). Analysis of 16S-23S intergenic transcribed spacer PCR (ITS-PCR) amplified by universal primers G1/L1 (Toth et al. 2001) and restriction fragment length polymorphisms generated by digestion with restriction enzymes Rsa I and Cfo I further demonstrated that KC20 isolate differed from P. carotovorum. BLASTn analysis of KC20 16S rDNA (GenBank accession no. MF155025) showed 99% nucleotide identity to that of P. aroidearum strain SCRI 109 (JN600323). Maximum likelihood phylogenetic trees based on 16S rDNA, pmrA sequences (KY021016)(Kettani-Halabi et al. 2013), and multilocus sequence analysis (Nabhan et al. 2012) of housekeeping genes (acnA, icd, gapA, mdh, mtlD, pgi, proA, and rpoS) (MF443741 to MF443748), all clustered KC20 into a clade containing other confirmed strains of P. aroidearum. Physiological tests, including 19 traditional physiological and biochemical tests and 94 phenotypes screened using the Biolog GN2 microplate system (Biolog, Haywood, CA), further confirmed our finding that the KC20 isolate was P. aroidearum (Nabhan et al. 2013). P. aroidearum exhibited a preference for monocotyledonous plants (Nabhan et al. 2013). This is the first report on occurrence of P. aroidearum in Chinese cabbage, which expanded the known host range for it, and also the first official report of the presence of P. aroidearum in Chinese territory.