First Report of Dickeya dianthicola Causing Potato blackleg in Oregon

Authors: MA, XING - Cornell University; FROST, KENNETH - Oregon State University; ZHANG, XIUYAN - University Of Maine; HAO, JIANJUN - University Of Maine; Swingle, Bryan

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Potato is susceptible to many diseases, including those caused by bacteria. In May 2023, about 24% of potato plants (variety ‘Russet Norkotah’) growing in a seed trial in Hermiston, Oregon, were smaller than normal and had brown and rotting stems. To determine the cause of the symptoms we isolated bacteria from the diseased plants and found bacteria that could break down plant material called pectin, which is a key diagnostic feature of a group of bacteria that cause disease in potato. The bacteria’s DNA was examined using genome sequencing methods, and the results showed the bacteria belonged to a group called Dickeya dianthicola. This group of bacteria has caused extensive potato diseases in the eastern United States and Canada, but it hadn’t been previously reported in Oregon. Healthy potato plants and tubers were infected with the bacteria and reisolated, confirming that these bacteria caused the disease and were responsible for symptoms as seen in the field in Oregon. This discovery is important because it shows that this harmful bacterium has reached Oregon. Farmers and scientists will need to be vigilant to prevent the disease from spreading further in the region.

Technical Abstract: In May 2023, a potato seed lot (variety ‘Russet Norkotah’) submitted to the Hermiston Agricultural Research and Extension Center (Umatilla County, Oregon) exhibited wilt and brown stem rot, with a 24% disease incidence (43/182 plants). Symptomatic plants were shipped to the USDA Emerging Pests and Pathogens Research Unit in Ithaca, NY, for pathogen identification. Pectinolytic bacteria were isolated from diseased stem tissue using crystal violet pectate (CVP) media. Two isolates, designated KF23-6 and KF23-8, were obtained and stored in glycerol at -80°C. Genomic DNA was extracted, sequenced using Illumina technology, and de novo assembled. Phylogenetic analysis revealed that the isolates clustered with Dickeya dianthicola. Genome-wide average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values confirmed species-level identity with D. dianthicola, though the isolates were distinct from the ME23 reference strain linked to previous outbreaks in the eastern US and Canada. ANI between KF23-6 and KF23-8 was 99.9936%, indicating clonality and that they are likely to be the same strain. Koch’s postulates were fulfilled through tuber and stem inoculations. Inoculated tubers and plants developed soft rot and blackleg symptoms. Pectinolytic bacteria re-isolated from symptomatic tissue were confirmed as the original inoculants via dnaX PCR and sequencing. This report represents the first detection of D. dianthicola in Oregon. Previously, this pathogen has been a major cause of soft rot and blackleg in northeastern and mid-Atlantic states, Florida, and parts of Canada. Its emergence in the Northwest highlights the need for increased surveillance and management strategies in this production region.