Diversity and pathogenicity of Pectobacterium species responsible for causing soft rot and blackleg of potato in the Columbia Basin

Authors: Rivedal, Hannah; BRAZIL, JESSIE - Oregon State University; FROST, KENNETH - Oregon State University

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2021
Publication Date: 7/14/2021
Citation: Rivedal, H.M., Brazil, J.A., Frost, K.E. 2021. Diversity and pathogenicity of Pectobacterium species responsible for causing soft rot and blackleg of potato in the Columbia Basin. American Journal of Potato Research. 98:267-284. https://doi.org/10.1007/s12230-021-09841-4.
DOI: https://doi.org/10.1007/s12230-021-09841-4

Interpretive Summary: Pectobacterium and Dickeya species cause multiple diseases of potato (Solanum tuberosum) including tuber soft rot, blackleg, aerial stem rot, and lenticel rot, which result in yield losses throughout the United States. The identities of bacterial species responsible for causing soft rot of potato have not been recently determined in the Columbia Basin of Eastern Oregon and Washington. In 2018 and 2019, 145 plant samples with symptoms of soft rot from the Columbia Basin were analyzed to identify the bacterial species causing disease. Soft rot bacteria species, including P. carotovorum (74.1%), P. atrosepticum (20.4%), and Dickeya species (5.6%), were detected in 51 samples using molecular identification. Twenty-eight bacterial isolates from the diseased samples were obtained in culture and their identity was determined through phylogenetic assessment of three gene sequences. Several isolates of P. parmentieri and P. brasiliense, were originally identified as P. caratovorum, indicating a need for more discriminatory diagnostic techniques. Pathogenicity was assessed by inoculation of tubers and stems of multiple potato cultivars. Interactions between Pectobacterium species, inoculation mixtures and soft rot/stem rot symptoms, were complex. However, inoculated alone, P. parmentieri and P. caratovorum caused high incidence of tuber rot and rot severity was enhanced when co-inoculated with other Pectobacterium spp. Inoculated alone, P. atrosepticum caused high incidence of stem rot, but co-inoculation with different Pectobacterium spp. did not always result in increased severity. Although Dickeya spp. may be present in the Columbia Basin, Pectobacterium spp. were the predominant pathogens with soft rot diseases of potato recovered in this study, contrary to reports from eastern US potato production regions. The species diversity within the Pectobacteriaceae isolates shows a need for more precise detection and diagnostic techniques, as these organisms can cause different symptoms and disease severity in Columbia Basin potato.

Technical Abstract: Pectobacterium and Dickeya species cause multiple diseases of potato (Solanum tuberosum) including tuber soft rot, blackleg, aerial stem rot, and lenticel rot, which result in yield losses throughout the United States. The identities of bacterial species responsible for causing soft rot of potato have not been recently determined in the Columbia Basin of Eastern Oregon and Washington. In 2018 and 2019, 145 plant samples with symptoms of soft rot from the Columbia Basin were analyzed to identify the bacterial species causing disease. Soft rot bacteria species, including P. carotovorum (74.1%), P. atrosepticum (20.4%), and Dickeya species (5.6%), were detected in 51 samples using PCR. Twenty-eight bacterial isolates from the diseased samples were obtained in culture and their identity was determined through phylogenetic assessment of dnaX, pelY, and 16s sequences. Several isolates of P. parmentieri and P. brasiliense, originally identified as P. caratovorum, were cultured. Pathogenicity was assessed by inoculation of tubers and stems of six and seven cultivars, respectively. Inoculated alone, P. parmentieri and P. caratovorum caused high incidence of tuber rot and rot severity was enhanced when co-inoculated with other Pectobacterium spp. Inoculated alone, P. atrosepticum caused high incidence of stem rot, but co-inoculation with different Pectobacterium spp. did not always result in increased severity. Although Dickeya spp. may be present in the Columbia Basin, Pectobacterium spp. were the predominant pathogens with soft rot diseases of potato recovered in this study. The species diversity within the Pectobacteriaceae isolates recovered has implications for the accurate detection and diagnosis of disease caused by these pathogens.