In a recent research article just published in Plant Disease, potato researchers in Maine and elsewhere examined 16 isolates associated with the Dickeya dianthicola outbreak in potato which began on the East Coast in 2015. This is a follow-up to an article published late last year looking into the origins of the outbreak. For more information on what was found in that study please click here. In their most recent study titled ‘Pangenomic analysis of Dickeya dianthicola strains related to the outbreak of Blackleg and soft rot of potato in the USA‘ eight distinct clades were distinguished based on phylogenomic analysis of 32 isolates with three clades (as previously reported) causing the outbreak on the East Coast in 2015, with the majority of isolates belonging to Clade I. Clade I strains were determined to be unique and homogeneous and the authors suggested they were a recent incursion from alternative hosts or environmental sources. The authors state the genomes of D. dianthicola isolates in Clade I possessed nearly identical genomics to that of isolate ME23 (previously identified in ME in 2015), and that each outbreak of the disease is typically caused by one predominant genotype due in part to contamination and spread of that genotype in one or a few widely used potato sources. The authors state that in the US, seed potatoes from a small number of sources in the northeast quarter of the US appeared to be important during the early stages of the outbreak, although, they (the authors) do not have enough evidence to explain how Clade I emerged and caused the outbreak. The authors suggested that while Clade I was predominant in causing the outbreak, other clades should not be ignored since these are present in the environment and additional outbreaks could occur since D. dianthicola has a wide host range and, clades currently not detected in the US could enter through trade in ornamental plants or seed.
