Phenotypic and Biolog-Based Identification of Pectobacterium Species Associated with Blackleg and Soft Rot of Potato in Pakistan.

Potato is a major commercial crop that is cultivated throughout the world. Blackleg and soft rot are potato diseases worldwide, caused by many species under the 2 bacterial genera Pectobacterium and Dickeya . These bacteria cause major loss in potato production, both in field and storage conditions. To study the incidence and prevalence of the blackleg and soft rot diseases, Attock (Bahtar Village) and Islamabad (Islamabad vegetable market) were visited. During the survey and sampling in Attock, incidence and prevalence of blackleg in field was recorded 10.6%, and 80% respectively. While in market tubers with soft rot disease incidence recorded as 8%. For isolation of the bacteria, potato plants showing the blackleg and tubers with soft rot symptoms were collected and brought into lab. Potato plants and tubers were washed with tap water. Small sections of tissues with blackleg and soft rot symptoms were cut into pieces and surface sterilized with 1% NaOCl solution or 70% ethanol. Tissue pieces were minced with sterilized mortar and pestle with 2-3ml sterile normal saline (0.85% NaCl) or sterile distilled water. The suspension was left for 15–20 minutes so the bacteria inside the diseased tissues release into solution. A loopful of bacterial suspension was streaked on CVP media and incubated for 2–3 days at 28ºC. After streaking on CVP media characteristic pits formation was observed. Bacteria from CVP media pits picked and streaked on NA for the purification and further identification. For further identification, colony morphology, biochemical testing (KOH, Catalase, Oxidase, Gram staining), pathogenicity (potato stem assay, potato tuber assay, bell pepper tissue maceration) and Biolog microbial identification system was performed. This is an automated technology that rapidly identifies the microorganisms. In Pakistan no report has been published recently to identify the blackleg and soft rot bacteria. Employing the Biolog identification system and comparing the readings on Biolog GEN III MicroPlates with database, revealed the detection of Pectobacterium carotovorum ss carotovorum B to cause the blackleg and soft rot diseases in potato.