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    Author(s): M. Botts
    Date: 2010
    Source: MS Thesis, Oregon State University. 92 pages.
    Publication Series: Miscellaneous Publication (MISC)
    PDF: View PDF  (6.45 MB)


    Colonization of N. densiflorus tissues by P. ramorum is not well understood. The pathogen is able to colonize nearly all tissues of this host but it is unclear how a tree is ultimately killed. Because this is such a destructive invasive pathogen, it is important to investigate its pathogenic strategy. Microscopic investigation of xylem colonization has been conducted, but colonization of bark tissues, which has always been regarded as an important part of infection, has not been investigated previously. In this research, P. ramorum infected N. densiflorus bark tissues were examined using various microscopic techniques to try to better understand the importance of bark infection in killing a tree. Host responses to infection were detected by various methods in conjunction with examining P. ramorum colonization, to try to better understand why the host is unsuccessful in stopping the pathogen. Results of this work indicate that the pathogen can colonize nearly all N. densiflorus bark tissues but that phellogen and parenchyma of the inner bark are the most frequently and densely colonized. A last piece of this work investigated the role of elicitins in pathogenicity during this interaction. These low molecular weight proteins have been implicated as having a role in pathogenicity in this and other phytopathogenic Phytophthora species. A fluorescent antibody was used to label elicitins in infected plant tissues to determine where they are produced, and what effect, if any, they appear to have on host cells. Elicitin labeling caused hyphal cell walls to fluoresce in plant tissues, contributing to an understanding of bark colonization more than to an understanding of the role of elicitins in promoting infection. Findings of this research show that nearly all bark tissues are capable of being colonized, that this host responds to infection in several ways, and that elicitins are present in cell walls of hyphae in infected plant tissues.

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    Botts, M. 2010. Histological Examination of Phytophthora ramorum in Notholithocarpus densiflorus Bark Tissues. MS Thesis, Oregon State University. 92 pages.

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