S14 - Session P4 - Effect of injury type and packaging material on the incidence and severity of postharvest soft rot on selected potato cultivars

Authors: Tlangelani Nghondzweni *, Reinette Gouws-Meyer, Retha Slabbert

Postharvest loss of potatoes due to soft rot bacteria, is one of the major challenges for the potato industry world-wide. Pectobacterium pathogens typically enters the tuber through injuries and natural openings, and rotting symptoms are mostly noticed during storage. Various forms of mechanical damage are found of which skin damage (abrasions) and bruising are the most important. For marketing purpose, potatoes are often packed in transparent plastic materials aimed at improving product presentation. This study aimed to investigate the effect of tuber injury type and packaging material on the incidence and severity of soft rot on various potato cultivars. Seven cultivars (cv.) (Mondial, Sifra, Valor, Fianna, Lanorma, Markies and Rumba) of freshly harvested potato tubers were selected for the study during harvesting of the national potato cultivar trials. Tubers were subjected to skin bruising and shallow tissue pricking as common injury types. Tubers were inoculated by immersion in liquid inoculum of Pectobacterium carotovorum for 60 seconds before subjected to washing. Tubers were airdried before packing in commercial potato paper bag and perforated plastic bag. Tubers were then incubated at room temperature and evaluated three times at 10 days interval using destructive sampling method. Results indicated that tubers with no injuries and packaged in paper bags maintained postharvest quality and prolonged shelf life as compared to tubers in plastic packaging. Tubers with tissue injury showed more soft rot expression as compared to tubers with skin bruising especially when packaged in plastic bags, with cv. Lanorma and Valor at 80% while Fianna and Rumba resulted in 100% soft rot incidence after 30 days in storage. Cultivar Markies proved to be tolerant to soft rot, maintaining tissue rot levels below 5% regardless of injury type and packaging material, throughout the storage period.