Abstract
Twenty, black stain root disease infected Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) from the Oregon Cascade and Coast ranges were dissected; macroscopic and microscopic patterns of fungal colonization are described. Ceratocystis wageneri Goheen et Cobb colonized secondary xylem, disrupting xylem transport. Histopathological studies revealed that the tracheid-limited pattern of colonization exhibited by this fungus is unique among Ceratocystis wilt pathogens. Axial colonization by hyphae was confined to xylem tracheids and radial development of mycelia in ray tracheids was limited. Parenchyma and cambial necroses did not result from direct hyphal attack. Living host cells, although not invaded, were responsive to hyphal attack of adjacent functional xylem. Secondary phloem was never invaded by hyphae, but some dysfunction was evident. Host responses to infection were unsuccessful in curtailing the spread of the pathogen.
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