The number, height and age of western hemlock dwarf mistletoe (Arceuthobium tsugense (Rosendahl) G.N. Jones) infections were recorded in two western hemlock (Tsuga heterophylla (Raf.) Sarg.) stands (44 and 130 years old) located on similar sites on the University of British Columbia Research Forest at Maple Ridge, B.C.. The rapid decrease in numbers of infections with infection age was shown to be largely due to infection mortality. The rate of intensification of the disease expressed as "doubling time" was estimated to be 40 or more years in both stands. Also estimated was a rate of vertical spread of .15 metres per year. The results differed markedly from those of other studies in similar stands, which generally predict "doubling times" of 2 to 4 years and vertical spread rates of up to .5 metres per year. / Forestry, Faculty of / Graduate

Thesis (M.S.)--Oregon State University, 1996. / Includes color map in pocket. Typescript (photocopy). Includes bibliographical references (leaves 96-103). Also available on the World Wide Web.

Anatomical and developmental tissue relationships between Arceuthobium spp. endophytic tissues and host vascular tissues were examined by light and transmission electron microscopes. The host-parasite pairs studied were Psudotsuga menziesii/A. douglasii, Tsuga heterophylla/A. tsugense, Pinus sabiniana/A. occidentale, and P. lambertiana/A. californicum. The morphological form and growth characteristics of A. douglasii in different aged host tissues was found to be coordinated with growth and maturation of the host. It is proposed that morphological forms of Arceuthobium endophytic tissue be categorized as (1) primary, (2) diffuse-secondary, or (3) localized-secondary in order to semantically clarify the relationship of endophytic morphology with primary or secondary growth stages of host tissue. In localized-secondary endophytic forms, the parasite integrates with host rays to form multiseriate infected rays. At both the light and electron microscope level, parasite cells can usually be identified by their distinctive chromocentric nuclei and abundant lipid bodies or lipid ghosts. Sinker cells of Arceuthobium have unusual plastids which resemble etioplasts and which do not store starch. Sinker cells have distinctive mitochondria with unusually large nucleoid areas. They have abundant endoplasmic reticulum. Wall/plasmalemma specializations increase the membrane surface area in relation to cell volume in sinker cells. The walls of host and parasite are fused at the middle lamella common to both organisms and the organisms share a common apoplast. Pit-like regions in the fused walls of the host/parasite interface were commonly seen in light microscope studies, although such interspecific pitting is seen less than intraspecific pitting. It was determined that, whereas intraspecific pits are traversed by complete plasmodesmata, interspecific pits had no plasmatic channels, or, only half plasmodesmata on the host side of the pit. In one case a half plasmodesmata was seen on the Arceuthobium side of the host/parasite interface. On the basis of the electron microscope studies of the host/parasite interface it appears that plasmatic connections between host and parasite do not normally occur. Because of this plasmatic isolation it can be concluded that nutrient acquisition does not involve direct flow of nutrients via interspecific symplastic bridges. Therefore, photosynthate, normally housed within phloem cells, must be leaked into the common apoplast of both host and parasite before becoming available for absorption into the parasite symplast. Since host and parasite lack symplastic continuity but share a common apoplast, apoplastically-mobile herbicides should be tested for their ability to accumulate in parasite tissues. Cytopathological effects on the host cells were relatively mild although a significant increase in the ratio of radial to axillary vasculature was noted in infected tissue. Other modifications included a tendency for increased numbers of specialized phloem parenchyma (Strasburger cells) in infected rays. No apparent anomalies were observed in conjunction with host sieve cell structure and development. The structure and ontogeny of healthy P. sabiniana phloem was also studied. It was found that the sieve element reticulum (SER) of mature sieve cells is derived from plastids during the maturation of the sieve cell. After maturation some of the SER membranes seem to disassociate into individual 60 (ANGSTROM) fibrils. These fibrils then reassociate and appear to be condensed into paracrystalline bodies which, in turn, participate in the generation of new membranes in the mature sieve cell. Because of their plastid origin, the SER membranes may have energy transducing and ionic pump capabilities that commonly are associated with plastid membranes. Such specialized functions of SER may contribute to the translocating capacities of sieve cells.

Fatty acid composition of five dwarf mistletoe species was analysed by Gas Liquid Chromatography. Because of the limitations of available equipment, only aerial shoots were analysed. Palmitic, oleic, linoleic and arachidic acids were the major components of total lipids. The sum of these acids accounted for 85-95 percent of total lipids present in the tissue. There was no apparent difference between species. The ratio of saturated acids to unsaturated acids in summer collections was higher than that of fall collections. Temperature may play an important role in controlling of these ratios. Lipid content varied from 3.25% to 8.5% on a dry weight basis depending on species.

Dwarf mistletoes are Parasitic flowering plants that infect conifer tree species. The effects of Arceuthobium americanum on the seed crop of Pinus contorta were examined over a two year period to evaluate the effects of altered host reproductive success on host population dynamics. Heavily infected trees produced significantly fewer cones than uninfected trees during the first season in which cones were collected. Cone length, number of seeds per cone, individual seed mass, and total calories per seed were significantly reduced in moderately and heavily infected trees. Trees with different levels of infection showed trends consistent with the above but no significant differences were observed during the second season. The number of seeds that were produced, disseminated, and that germinated per square meter of forest floor was significantly less in heavily infected plots than in lightly infected plots. Survival of one year old seedlings, however, was significantly higher in heavily infected plots. Significant increases in the abundance of woody litter due to increases in mortality of mature trees and witches brooms were positively correlated with increases in seedling survival in heavily infected plots. Survival of trees less than 45 years of age also increased as the level of infection in plots increased. This increases the fraction of total density that saplings represent in heavily infected stands. The total basal area of plots with different levels of infection were uniform, implying that all available environmental resources are being utilized. The differences in age distribution between lightly and heavily infected plots, however, indicate that resources are partitioned differently between saplings and mature trees in plots with different levels of infection. Dominant host trees experienced higher mortality in heavily infected plots than in lightly infected plots. This reduces the total biomass of all mature trees. Increased mortality of dominant host trees frees resources which reduces intraspecific competition thereby contributing to increased sapling survival in heavily infected plots. Consequently, stand density increases as the level of infection increases.

Arceuthobium americanum is a flowering plant which parasitizes Pinus contorta (Lodgepole pine). This study examined branch performance of P. contorta infected to varying degrees with A. americanum.

No description available.

No study has been done in the western United States concerning dispersal of dwarf mistletoe by mammals. At the outset of the study it was determined that the red squirrel, the yellow pine chipmunk (Eutamias amoenus), the northern flying squirrel, and the bushy-tailed wood rat (Neotaoma cinerea), were all potential vectors of seeds. The red squirrel was chosen as the main object of study because it is diurnal and is closely associated with ponderosa pine (Pinus ponderosa), a heavily infected species. The study was undertaken to determine whether small mammals play a significant role in transporting mistletoe seeds to uninfected areas. Understanding their role can be helpful both in further understanding of the biology of dwarf mistletoe and in evaluating current control practices.

Cytokinin levels were determined by bioassay on a seasonal basis, for two species of dwarf mistletoes (Arceuthobium douglasii and Arceuthobium tsugense) and their respective hosts, Douglas-fir (pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). The highest cytokinin levels occurred in early Spring for all of the samples studied. However, with the exception of the first growth segments of Douglas-fir, the levels of cytokinins detected were significantly greater in infected tissue and aerial shoots of the mistletoe than in the healthy tissue. Further studies were carried out on Spring and Winter samples to determine the kinds of cytokinins present. High performance thin layer chromatography and gas liquid chromatography results showed that zeatin riboside (ZR) was the only detectable cytokinin in Winter samples. ZR was also detected in all Spring samples excepting the aerial shoots of A. douglasii. Two other cytokinins were also detectable in Spring samples. Zeatin was present in aerial shoots from both dwarf mistletoes and in the infected fifth growth segments from Douglas-fir and in infected western hemlock tissue. Zeatin occurred in the healthy tissue only in first growth segments of Douglas-fir. The 2iPA was detectable in the aerial shoots of the dwarf mistletoe, in the fifth grmvth segments of Douglas-fir, and in the infected tissue from western hemlock. These results are discussed with particular reference to the role of cytokinins in the physiological interactions between the host and the parasite.

Germination, respiration, and photosynthesis in seeds of dwarf mistletoe (Arcenthobium) were studied. The effects of 1 hour soakings of seeds in aqueous solutions of 1, 2, or 3% H2O2 or 1, 2, 3, 4, or 5% Chlorox on germination of seeds were tested. Germination rates for seeds from three consecutive years (1975-1977) were obtained. Germination rates varied widely. This variance transcended subtle changes in treatment. Pretreatment of seeds with Chlorox resulted in significantly lower germination rates than those of the control. Chlorophyll concentrations were determined for seeds and aerial shoot tissue of four species. Seeds of A. douglasii had the highest chlorophyll concentration (0.39 mg/g fresh weight) while seeds of A. tsugense had the lowest concentration (0.25 mg/g fresh weight). Net O2 uptake by seeds of A. campylopodum in dark and in light was measured by manometric and polarographic methods. The mean values were 353 μl O2 g-1 h-1 in the dark and 201 O2 g-1 h-1 in the light. The difference between these rates is apparently due to O2 evolution during photosynthesis. In light the seeds can fix 43% of the CO2 produced by respiration. Experiments in which seeds were exposed to 14CO2 in light confirmed that the seeds are able to fix CO2. Extraction of seeds with ethanol showed that 97-99% of the incorporated 14C was ethanol soluble. Ten to sixteen percent of the ethanol fraction was chloroform soluble while the rest was H2o soluble. Ion exchange separation of the H2o phase showed that 11-25% of 14C activity was cationic, 15-29% anionic, and 53-67% neutral.