Co-occurrence of latent Dickeya and Pectobacterium species in potato seed tuber samples from northern Finland

Recent methodological developments have uncovered the etiological diversity of the potato blackleg and soft rot Pectobacteriaceae. At least five species in the genera Dickeya and Pectobacterium have been confirmed to cause blackleg on potatoes in Finland. The bacteria are seed borne and remain latent in the tuber until conditions favourable for growth, multiplication and infection prevail. Tubers could be infected by one or more of these species. This short communication is based on the results of molecular detection data collected for more than 14 years from potato seed lots produced in Finland. Diagnostic PCR assay specific to Dickeya solani, Pectobacterium atrosepticum, Pectobacterium carotovorum, P. brasiliense and P. parmentieri revealed that potatoes are infected by one or more of these species; it also revealed that single species infection is more common than multiple colonization. An event of simultaneous occurrences of different strains from the Pectobacterium species appears to be more frequent than that observed between Dickeya and Pectobacterium species. The absence of co-occurrence of Dickeya solani and Pectobacterium atrosepticum is intriguing.