Detection of Ralstonia solanacearum in Asymptomatic Imported Seed Potato using a DNA-based Method

Potato is an economically important crop among vegetables grown in Sri Lanka that mainly relies on healthy seed potatoes. About 40% of the annual seed potato requirement is fulfilled by the import of seed potatoes from Netherland, USA, Germany and France. Import of seed potatoes makes possibilities to enter plant pathogenic pests and diseases to Sri Lanka. Bacterial wilt is one of the most destructive diseases of potato. Ralstonia solanacearum, which causes bacterial wilt of potato, is considered as an important quarantine significant plant pathogen in Sri Lanka. The currently available conventional methods such as culture methods, biochemical methods are time consuming, very laborious and not sensitive for the detection of R. solanacearum in imported seed potatoes. Although immunodiagnostic methods are rapid, the sensitivity is not enough to detect the bacterium in asymptomatic or latently infected seed potatoes. In this study, a DNA-based detection method was applied to screen seed potatoes imported into Sri Lanka and 5 out of 30 tested samples (17%) were positive for R. solanacearum. The seed potato samples detected as infected with R. solanacearum were further studied and it revealed that the Asian phylotype I and the American phylotype II were detected from seed potato samples imported to the country. Phylotype II (Race 3/biovar 2) was detected in seed potatoes imported from USA and France and both phylotype I and phylotype II (Race 3/biovar 2) were detected in seed potatoes imported from Netherland from where majority of seed potatoes are imported into the country. The quarantine measures should be strictly followed to avoid the spread and establishment of phylotype II, Race 3/biovar 2 strains within the country, as it is the extremely destructive potato pathogen which have a restricted distribution in higher elevations of Sri Lanka. Further, the DNA-based method can be used to identify the pathogen to avoid the introduction or entry of R. solanacearum into the country for the betterment of potato cultivation in Sri Lanka. KEYWORDS: Seed potato, Bacterial wilt, Ralstonia solanacearum, Quarantine pest, Rsol_fliC