Graduate Thesis Or Dissertation
 

Anatomical studies of Pinus ponderosa Laws : infested by Elytroderma deformans (Weir) Darker

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/70795c05q

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  • Pine needle blight of Pinus ponderosa Laws. caused by Elytroderma deformans (Weir) Darker is recognized by changes in the needles, in the bark and in the development of the branches. Anatomical studies of the host-parasite relation have been made previously on young pine tissue up to four years of age but not on older tissues. Neither has the pattern of invasion been worked out in individual plants. Permanent microsections using standard methods of micro-technique were made on material collected from Round Mountain and from the Pringle Falls Experimental Forest near Bend, Oregon. Normal bark development was studied in noninfected trees from age one through 25. Comparisons made with infected stems revealed: 1. Whereas deep periderms do not occur in uninfected stems up to 25 years old they do occur in infected stems anytime after the second year. The cork cambiums which arise within parenchyma cells of the primary and the secondary phloem in association with hyphal invasion of sieve cells ultimately produce pathological resin canals. Hyphal degeneration results and tissues external to the wound periderms become necrotic. These reactions are generalized responses such as any tissue makes to a foreign agent. However, there is no straight-line relationship between the intensity of tissue response and the severity of the invasion. Z. In stems, hyphae are confined entirely to the sieve cells of the phloem. They may spread vertically within a specified phloem layer and radially from one growth increment to the next. 3. When hyphae invade secondary phloem sieve cells close to the vascular cambium, the vascular cambium is stimulated to produce abnormal parenchyma cells. 4. Phloem horizontal resin canals are more abundant in infected than in noninfected tissue. 5. Sclereids occur in larger groups and more abundantly in both the cortex and the pith of infected stems. 6. Mycelia and microscopic anatomical changes may be present within stems which are macroscopically asymptomatic and bear .green needles. The distribution of hyphae within infected trees was determined by free-hand sections of suppressed ponderosa pine saplings up to 30 years old. Hyphae were found in stem tissue up to 20-years-old. Evidence is conclusive for hyphal growth from the trunk along branches toward growing tips and is suggestive of growth from apical meristems toward the trunk.
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