Characterization of host and non-host interactions of the bacterial wilt pathogen, Erwinia tracheiphila
Bacterial wilt, caused by insect-transmitted Erwinia tracheiphila, is one of the most devastating diseases of cucurbit crops in the United States. Yield losses on susceptible cucumber ( Cucumis sativus), melon (Cucumis melo), and squash (Cucurbita pepo) cultivars reach up to 80%. Despite its economic importance, the pathogen has received inadequate research attention due to the prevalence and success of insecticidal sprays to control the vectors—a conventional disease management strategy—in addition to the pathogen’s difficulty being isolated and manipulated in the laboratory. As a consequence, the pathogenic mechanisms and basic biology of the bacterium are poorly understood. To answer basic questions and investigate more about the pathogen, I aimed to characterize how E. tracheiphila behaves in both compatible and incompatible systems. The first part (Chapter 2) confirms a previous finding that different strains of the pathogen possess specific compatibility with different cucurbit hosts. I developed modified inoculation and disease assessment methods and validated host-specificity of the strains. Cucumber, melon, and squash plants were inoculated with selected strains HCa1-5N, UnisCu1-1N ( Cucumis strains) and MISpSq-N (Cucurbita strain). The results suggest that Cucumis strains are more virulent in cucumber and melon but less virulent in squash. Similarly, the Cucurbita strain is more virulent in squash than in cucumber and melon. The second part (Chapter 3) discusses the incompatible, non-host interaction of the pathogen with tobacco (Nicotina tabacum). The induction of hypersensitive response (HR) as an immunity reaction in non-host plants is one of the classic characteristics of Gram-negative phytobacteria. I surveyed 21 E. tracheiphila strains for HR induction, characterized the plant physiological changes during the response, compared the sequences of the HR-inducing protein Harpin (HrpN), and conducted a HrpN-based phylogenetic analysis among erwiniae. The results indicate that E. tracheiphila induces authentic HR in tobacco through its HrpN protein, similar to other known HR-inducing Erwinia species. These findings provide basic information about the pathogen that can be exploited to develop more resistant cucurbit cultivars. For instance, the host-specific mechanism can be used to create host-pathogen incompatibility in susceptible hosts and lessen the ability of the pathogen to cause disease.^
Eric S Nazareno,
"Characterization of host and non-host interactions of the bacterial wilt pathogen, Erwinia tracheiphila"
ETD Collection for Tennessee State University.