Potato Seed Decay and Stand Loss is Not Caused by Dickeya Spread during Cutting and Handling of Seed Potatoes

Soft rot bacteria are the main cause of early seed decay and stand losses in field grown potatoes. These bacteria are present in most surface water and colonize lenticels of early generation seed potatoes and cause disease when conditions are favorable for bacterial growth. Soft rot bacteria, formerly in the genus Erwinia , have been reclassified into the genera Dickeya and Pectobacterium. Because of their ubiquitous association with potato tubers, it is assumed that the soft rot bacteria is spread during handling and planting of seed potatoes and can potentially cause seed decay and blackleg. A soft rot bacterium new to the United States, Dickeya dianthicola was first recognized in 2015 (Secor, unpublished) as the cause of serious stand losses of potatoes in production sites in the eastern US. Replicated and commercial field trials using seed laboratory inoculated and naturally infected with D. dianthicola were conducted in multiple locations to determine spread from infected seed potatoes to healthy seed potatoes during handling and cutting. There is no evidence of increased stand losses or blackleg after simultaneous handling and cutting of Dickeya infected seed potatoes with seed potatoes free of Dickeya. Laboratory trials with labeled soft rot bacteria demonstrated spread of bacteria by cutting knives. There may be other factors that prevent establishment and infection by soft rot bacteria that may spread during seed potato cutting that need to be investigated. We conclude that spread of Dickeya bacteria during handling and cutting of seed potatoes is not a major cause of subsequent seed decay and blackleg resulting in increased stand losses in the field.