First Report of Orostachys malacophyllus Soft Rot Caused by Pectobacterium carotovorum subsp. carotovorum in Korea

Abstract

HomePlant DiseaseVol. 100, No. 1First Report of Orostachys malacophyllus Soft Rot Caused by Pectobacterium carotovorum subsp. carotovorum in Korea PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Orostachys malacophyllus Soft Rot Caused by Pectobacterium carotovorum subsp. carotovorum in KoreaY. S. Kim and Y. JeonY. S. KimSearch for more papers by this author and Y. JeonSearch for more papers by this authorAffiliationsAuthors and Affiliations Y. S. Kim Y. Jeon , Department of Bioresource Sciences, Andong National University, Andong 760-749, Korea. Published Online:28 Oct 2015https://doi.org/10.1094/PDIS-04-15-0413-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Orostachys malacophyllus is a perennial herbaceous plant belonging to the family Crassulaceae that is found widely in Korea, China, and Japan. The plant is typically harvested from summer to autumn, and is used for medicinal purposes after removing its roots and then drying under sunlight (Park et al. 1991). It has been observed that the plant becomes more susceptible to infection when cultivated. For our survey, we collected plants from plantations near Uljin in Gyeongbuk Province during the summers of 2013 and 2014. The early symptoms of plant disease were water-soaked lesions on leaves, starting from base of the stem. Thereafter, the lesions expanded rapidly over the entire plant, resulting in a soft rot of the plant. From July to August, after rainfall, disease incidence rapidly increased from 30 to 80%. In order to isolate the causal agent of the water-soaked lesions, 1-cm leaf segments were surface sterilized in 70% ethanol and 1% NaOCl solution for 30 s, rinsed and macerated in sterile distilled water, and then plated onto nutrient agar medium. Bacterial colonies developed on all the plates after incubation for 48 h at 28°C. Isolated bacteria were gram-negative, oxidase-negative, facultatively anaerobic, positive for degradation of crystal violet pectate agar (CVP), nonfluorescent on King’s B medium, positive for hypersensitive response in tobacco plants, and caused soft rot of potato tubers. To further identify the bacterial strains, we performed Biolog, fatty acid methyl ester (FAME), and 16S rDNA sequence analyses. The Biolog GN2 microplate and the Release 4.20 system putatively found the strain to exhibit 85% similarity with the bacterium Pectobacterium carotovorum subsp. carotovorum. Likewise, analysis of FAME profiles using the Microbial Identification System (Sherlock version 3.1, Microbial Identification System, Newark, DE, USA) also characterized the representative bacterial strain as P. carotovorum subsp. carotovorum with 89% similarity. The isolated bacterium’s 16S rDNA was amplified by PCR using the primer set 27F (5′-TCCGTAGGTGAACCTGCGG-3′) and 1492R (5′-TTCTCCGCTTATTGATATGC-3′) (Weisburg et al. 1991; Cheon et al. 2014), and subsequently subjected to a similarity search using BLAST analysis of the NCBI database. The 16S rRNA gene sequence from the strain (GenBank Accession No. KT222000) showed 99% identity with sequence of P. carotovorum subsp. carotovorum previously deposited in GenBank (KC790305). Pathogenicity of the three strains was confirmed by dropping a bacterial suspension (20 µl per inoculation site, 1 × 108 CFU/ml) onto leaf surfaces in a growth chamber maintained at 28°C and 80% relative humidity. Two leaves were inoculated with each strain, and the experiment was conducted twice. Sterile distilled water was used as the control. Water-soaked lesions appeared on the inoculated leaves within 48 h of inoculation, in contrast to the control leaves, which showed no symptoms. The bacteria were reisolated from the leaf showing symptoms and confirmed as P. carotovorum subsp. carotovorum by Biolog. To our knowledge, this is the first report of P. carotovorum subsp. carotovorum as a pathogen of O. malacophyllus in Korea.