First report of pectobacterium brasiliense causing bacterial blackleg and soft rot on potato in Pennsylvania

Authors: ZHANG, XIUYAN - University Of Maine; MA, XING - Cornell University; FAN, XIAOWEI - University Of Maine; GE, TONGLING - University Of Maine; LEIBY, ROBERT - Pennsylvania Co-Operative Potato Growers; Swingle, Bryan; JOHNSON, STEVEN - University Of Maine; Larkin, Robert - Bob; CHIM, BEE KHIM - University Of Maine; HAO, JIANJUN - University Of Maine

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2023
Publication Date: 2/12/2023
Citation: Zhang, X., Ma, X., Fan, X., Ge, T., Leiby, R., Swingle, B.M., Johnson, S., Larkin, R.P., Chim, B., Hao, J. 2023. First report of pectobacterium brasiliense causing bacterial blackleg and soft rot on potato in Pennsylvania. Plant Disease. 107(8):36774584. https://doi.org/10.1094/PDIS-09-22-2085-PDN.
DOI: https://doi.org/10.1094/PDIS-09-22-2085-PDN

Interpretive Summary: This paper reports the first identification of Pectobacterium brasiliense causing bacterial blackleg and soft rot on potato in Pennsylvania. An outbreak of diseased potato plants was found at a commercial potato production farm in Harrisburg, Pennsylvania. We received samples of the diseased plants for diagnosis and to identify pathogens responsible for causing the disease. We used multiple molecular methods to determine the genus and species of bacteria isolated from the disease plants, which we identified as Pectobacterium brasiliense. We confirmed that this was the pathogen responsible by infecting healthy plants, which quickly developed disease symptoms that were similar to what was observed at the potato farm. We then reisolated the bacteria from the diseased plants and used molecular methods to show that the same bacteria were responsible for the disease in our test. This is the first time that Pectobacterium brasiliense has been identified in Pennsilvania, USA.

Technical Abstract: Potato plants showing blackleg symptomatic stems were collected in August 2021 from a farm in Harrisburg, PA. To identify the pathogen, diseased stems were cut at the soil line, surface disinfected, and placed into sterile water to allow bacteria to release into the water. The bacterial suspension was streaked on crystal violet polypectate (CVP) medium and incubated. Single, well-isolated colonies were observed to form cavities on the medium, were picked, and purified by re-streaking on CVP plates. Genomic DNA of each isolate was extracted and used for polymerase chain reaction (PCR) with the primer pairs to amplify the gapA and recA genes. The sequence of the aplicons were used to search for matches in the NCBI database. Results showed that theses genes had between 99.86% and 100% identity with Pectobacteium brasiliense. A greenhouse trial was established to conduct Koch’s postulates. The stems of three potato plants and three tubers were inoculated with a suspension of the isolated P. brasiiense or sterile medium as a control. The stems and tubers inoculated with the bacterium had black and rotten tissues after seven or four days,respectively. Whereas the control plants remained symptomless. We reisolated bacteria from the diseased tissues and confirmed them to be the same P. brasiliense strain using PCR and DNA sequencing as described above. To our knowledge, this is the first report of blackleg and soft rot of potato caused by P. brasiliense in Pennsylvania.