Abstract
An outbreak of bacterial soft rot and blackleg of potato has occurred since 2014 with the epicenter being in the northeastern region of the United States. Multiple species of Pectobacterium and Dickeya are causal agents, resulting in losses to commercial and seed potato production over the past decade in the Northeastern and North Central United States. To clarify the pathogen present at the outset of the epidemic in 2015 and 2016, a phylogenetic study was made of 121 pectolytic soft rot bacteria isolated from symptomatic potato; also included were 27 type strains of Dickeya and Pectobacterium species, and 47 historic reference strains. Phylogenetic trees constructed based on multilocus sequence alignments of concatenated dnaJ, dnaX and gyrB fragments revealed the epidemic isolates to cluster with type strains of D. chrysanthemi, D. dianthicola, D. dadantii, P. atrosepticum, P. brasiliense, P. carotovorum, P. parmentieri, P. polaris, P. punjabense, and P. versatile. Genetic diversity within D. dianthicola strains was low, with one sequence type (ST1) identified in 17 of 19 strains. Pectobacterium parmentieri was more diverse, with ten sequence types detected among 37 of the 2015–2016 strains. This study can aid in monitoring future shifts in potato soft rot pathogens within the U.S. and inform strategies for disease management.
Highlights
Licensee MDPI, Basel, Switzerland.In 2020, potatoes were, by weight, the fifth most produced food crop globally, behind sugar cane, maize, wheat, and rice [1]
Soft rot bacteria analyzed in this study included 113 strains isolated in 2015 and 2016 from symptomatic potato tissues collected in production and testing fields in Northeastern and North Central USA
The phylogeny predicted by concatenated dnaJ, dnaX, and gyrB sequences placed several reference and 2015–2016 strains, some previously identified only to genus, within clades containing type strains of D. chrysanthemi, D. dianthicola, D. dadantii, and D. zeae (Figure 1; Tables 1–3)
Summary
Pectolytic soft rot diseases cause annual field and storage losses in potato production [3,4,5]. To address continued concerns about the impacts of soft rot diseases on potato production and to increase awareness of the soft rot pathogens present in the U.S, a multi-state survey was conducted to identify the taxa of Pectobacterium and Dickeya present in the Northeastern and North Central U.S during 2015–2016. Pectobacterium parmentieri [19] emerged from the surveys as another pectolytic soft rot pathogen associated with recent aerial soft rot outbreaks in Maine, New York, Minnesota, North Dakota, and Michigan [15,19,20,21,22]. Our findings confirm that soft rot diseases in the U.S potato industry are caused by a wide range of Dickeya and Pectobacterium species
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