First Report of Pectobacterium atrosepticum, Causing Bacterial Soft Rot on Calla Lily in Serbia

Abstract

In 2015, bacterial soft rot symptoms on calla lily (Zantedeschia aethiopica L.) were found in greenhouse in Kraljevo area, Serbia, with a disease incidence of 20 to 30%. The disease was characterized by water-soaked necrotic lesions on leaves and stems, resulting in collapse of whole plants. Small pieces of leaf tissue, taken from the margin of necrotic lesions, were homogenized and spread onto nutrient agar (NA). After incubation for 48 h at 26°C, single creamy white, round, and convex bacterial colonies were formed. Eight representative isolates (PC1 to PC8), randomly selected for further identification, produced characteristic pits on crystal violet pectate medium (CVP) (Perombelon and Van der Wolf 2002) and showed pectolitic activity by developing rotted tissue on the inoculated potato tuber slices. All isolates were gram-negative, rod shaped, facultative anaerobic, nonfluorescent on King’s B medium; positive for catalase, hypersensitive response on tobacco and nitrate reduction; negative for oxidase reaction, production of levan, arginine dihydrolase, and indole. Differentiation tests among Pectobacterium spp. (Perombelon and Van der Wolf 2002) resulted in negative growth at 37°C, and positive reaction for the production of reducing substances from sucrose. Isolates were further characterized on the basis of sequence analysis of the housekeeping genes gapA and mdh (Ma et al. 2007). Sequences were deposited in the National Center for Biotechnology Information (NCBI) GenBank database for mdh (MF109822–29) and gapA genes (MF109830–37) for the isolates from PC1 to PC8, respectively. BLAST analysis revealed 97% homology (Query coverage 100%; E. value 0.0) with Pectobacterium atrosepticum strains 21A (CP009125) and JG10-08 (CP007744). Pathogenicity was tested on leaf petioles of calla lily plants by injecting with a bacterial suspension (107 to 108 CFU/ml), and incubated at room temperature and 70 to 80% relative humidity (Ni et al. 2010). Three replicates for each isolate were used. After a 24 h period, the inoculated calla lily plants exhibited the rot symptoms, initially presented as light brown lesions at the inoculation sites, which further resulted in dissemination to surrounding tissue, its maceration, and cell death after 3 days. No symptoms were observed on controls inoculated with sterile distilled water. Reisolates produced characteristic pits on the CVP medium. To our knowledge, this is the first report of soft rot caused by P. atrosepticum on calla lily in Serbia. Further research will be performed in order to determine how far the disease is spread to other area or hosts in Serbia.