Date of Award
Spring 5-10-2025
Level of Access Assigned by Author
Open-Access Thesis
Degree Name
Doctor of Philosophy (PhD)
Department
Ecology and Environmental Sciences
First Committee Advisor
Jianjun Hao
Second Committee Member
Robert P. Larkin
Third Committee Member
Gregory Porter
Additional Committee Members
Seanna L. Annis
Ek Han Tan
Abstract
The potato (Solanum tuberosum) plays an important role in global food security. However, its production is severely threatened by diseases like potato blackleg and soft rot (PBSR), which are caused by many species of Dickeya and Pectobacterium. This research aimed to identify and characterize bacterial species associated with PBSR, evaluate their pathogenic potential, and investigate interactions among bacterial communities affecting disease dynamics. A total of 196 bacterial strains were isolated from these samples from 2015 to 2023, which were analyzed using molecular approaches.
The study identified Dickeya dianthicola and Pectobacterium parmentieri were predominant in 2015 and 2016, but recent sampling indicated these species were replaced by newly dominant species P. versatile and P. carotovorum. Additionally, P. punjabense and P. parvum were found for the first time in Maine. Although single-specie infections were common, multiple species were frequently isolated from the same plant sample, suggesting potential interactions among the pathogens.
Pathogenicity assays demonstrated that Dickeya dianthicola genotype I was more virulent than genotypes II and III, confirming a major role in the 2015 PBSR outbreak. Tuber inoculations showed that P. parmentieri and P. carotovorum were less pathogenic than D. dianthicola, however, P. parmentieri was more aggressive across a wider temperature range. Co-infections of one of the Pectobacterium spp. with D. dianthicola generally resulted in larger lesions.
A phylogenetic tree constructed based on single nucleotide polymorphism (SNP) data showed that P. brasiliense, P. parmentieri, P. atrosepticum, P. polaris, P. versatile, P. carotovorum showed more diverse and distinct evolutionary relationship with international strains. The type III secretion system is completely absent in P. aquaticum and P. parmentieri. also completely lacked the type Va secretion system was not found in P. aquaticum, while both P. parvum and P. punjabense lack type VI secretion system subtype I. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway map showed that the general metabolic pathway was the most significantly enriched pathway, indicating that P. versatile may have a wider or more specific metabolic capacity, which to some extent explains its widespread distribution in recent years.
Recommended Citation
Zhang, Xiuyan, "Genetic And Biological Characterization Of Bacterial Complexes Causing Potato Blackleg And Soft Rot" (2025). Electronic Theses and Dissertations. 4131.
https://digitalcommons.library.umaine.edu/etd/4131