Pectobacterium and Dickeya Responsible for Potato Blackleg Disease in New York State in 2016

Beginning in 2014, outbreaks of blackleg disease compromised potato (Solanum tuberosum) production in the northeastern United States. Disease severity was atypical for plantings with certified seed. During 2016, 43 samples with blackleg symptoms were analyzed, originating from more than 20 farms operating in New York State. A combination of techniques was employed to identify the blackleg pathogens: isolation in vitro, diagnostic PCR assays for Pectobacterium and Dickeya sp., pathogenicity assays, and DNA sequencing. Twenty-three bacterial isolates were obtained, the majority of which were designated D. dianthicola or P. parmentieri; two of the isolates were designated P. atrosepticum. All isolates were pathogenic in stem lesion and tuber soft rot assays and exhibited pectin degrading activity (pitting) in crystal violet pectate agar medium. Phylogenetic analyses of dnaX gene sequences placed all but one of the isolates into clades corresponding to D. dianthicola, P. parmentieri, or P. atrosepticum. One atypical isolate clustered with P. carotovorum subspecies. Data are consistent with the hypothesis that D. dianthicola from New York and the northeast are part of a single clade, and at least three different soft rot bacteria were associated with blackleg during 2016 in New York.