Assessment of certain plant extracts for controlling potato tuber soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum

The study aimed to evaluate the effectiveness of three plant extracts (cumin (Cuminum cyminum L.), peel fruit of pomegranate (Punica granatum), and fruit of black pepper (Piper nigrum L.)), against Pectobacterium carotovorum subsp. carotovorum (Pcc), a bacterium that causes potato tuber soft rot disease. This disease can result in significant losses to potato production and affects the quality of potatoes during storage, transit and shipment. To conduct the study, five isolates of the pathogenic bacterium were obtained from naturally infected potato tubers. According to the in vitro screening, the most virulence isolate Pcc2 was molecularly identified using 16S rRNA gene partial sequencing. Three plant extracts (cumin, pomegranate, and black pepper), were tested for their antibacterial activity against the bacterium using in vitro experiments. The results showed that all the three plants extract exhibited inhibition of the bacterial growth. Among the three-plant extract, pomegranate was found to have the best inhibitory effect on the bacterium (0.92 cm inhibition zone). Based on the findings of the in vitro experiments, the use of all extract at a concentration of 50 mg was recommended for controlling the soft rot disease in potato tubers during storage conditions. The data demonstrated that pomegranate extract was on the first ranking with bacterial growth reduction percentage estimated (1.4 mm), followed by cumin extract with growth reduction estimated (0.92). The data revealed that all of the tested plant extracts were able to reduce the severity of the disease. Of all the extracts, pomegranate extract showed the highest reduction in disease severity (91.3%). It is evident that the treatments with pomegranate, black pepper, and cumin consistently led to an increase in total phenol content over the course of 21 days. Treatments with methanolic extract of pomegranate, black pepper, and cumin lead to varying degrees of increased peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities over the course of the experiment. The data shows that the effectiveness of these treatments generally increases with time. In conclusion, the study showed that all plants extract tested herein has the potential to control potato tuber soft rot disease, which is a major problem affecting potato production.