AN OUTBREAK OF THE SOFT ROT ON CABBAGE

Abstract

Soft rot disease is present on a wide range of plant species worldwide. The symptoms are similar in most hosts and can be easily recognized by soft, wet, cream colored flesh often surrounded by a dark margin. The disease progress is followed by the occurrence of a specific smell. Bacterial species mainly belonging to the genus Pseudomonas and Pectobacterium are responsible for soft rot disease. During July 2018 bacterial soft rot symptom on cabbage (Brassica oleracea var. capitata L.), in form of water-soaked lesions on leaves with specific odour was observed in Semberija area. Disease inci dence ranged between 20-30%. The objective of this research was to identify the causal agent of the soft rot disease associated to the cabbage outbreak. Collected samples of symptomatic cabbage plants were subjected to isolation of pathogen and its identification. Leaves of cabbage plants were first washed under tap water, and then dried at room temperature. Isolation was performed using homogenized pieces of leaf tissue taken from the margin of necrotic lesions in sterile distilled water and plated on Nutrient Agar (NA), King’s B and Crystal Violet Pectate mediums (CVP). After incubation time at 26°C for 48 h, most of the formed bacterial colonies were creamy-white, round and convex. Eight representative isolates which pro duced characteristic pits on CVP were further identified on the basis of conventional bacteriologi cal methods and polymerase chain reaction (PCR) using three primer sets: F0145 / E2477 (specific for Pectobacterium carotovorum subsp. carotovorum), Br1f / L1r (specific for P. carotovorum subsp. brasiliensis) and ECA1f / ECA2r (specific for Pectobacterium atrosepticum). Isolates were genetically characterized on the basis of sequence analysis of the gapA and mdh housekeeping genes. All isolates were gram negative, rod shaped, facultative anaerobe, oxidase negative, catalase positive, nonfluorescent on King’s B medium, levan and arginine dihydrolase negative. They were able to cause soft rot on cabbage and potato tuber slices 24 h after inoculation with bacterial sus pension, under high relative humidity conditions. PCR results showed that isolates produced 666 bp band using F0145 / E2477 praimer pair and belong to bacterium P. carotovorum subsp. carotovorum. BLAST analysis of gapA and mdh housekeeping genes confirmed the identity of the isolates with P. carotovorum subsp. carotovorum strains deposited in NCBI database M34 (KY047594) for gapA and Pcc t0437 (KC337296) for mdh with 99.39% (Q. cover 100%, E. value 0.0) and 100% (Q. cover 100%, E. value 0.0) homology, respectively. Considering that there is no effective treatment against soft rot bacteria, and that prevention is the only way for their control, early detection and identification of causing pathogen plays a key role in suppression of the disease spread.