Arceuthobium americanum is a vascular plant which is parasitic upon Pinus contorta var murrayana. Its documented effects include reductions in host growth, vigor and wood quality. The specific physiological changes that occur in the host are, for the most part, unknown.

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This dissertation describes arthropod responses to and effects on decay processes in ponderosa pine, a dominant forest canopy tree in northern California. We used both descriptive and experimental field techniques to establish how arthropod assemblages depend on and are important to the disintegration of woody structures in forests of this type. The first study used pitfall traps placed within and on the outsides of fallen, large old ponderosa pine trees to establish the effects of microenvironments created during tree death. We studied the internal and external structures of fallen trees as well as the forest floor in canopy gaps and in the surrounding undisturbed forest. Five trees were surveyed, representing a decay sequence from newly dead and with distinct canopy gap, to well-decayed with recovering canopy. Arthropod assemblages were distinct among the different microenvironments, but were less so with increasing tree/gap age. Differences between tree and soil faunae decreased with increasing decay, as did the differences between gap and non-gap catches from the forest floor. The second study used experimental exclusion techniques to examine how longitudinal (bark beetle) and transverse (woodboring) insect colonists could influence rates of mass loss and carbon respiration from young, dead ponderosa pine. We found that both groups enhanced the prevalence of staining fungi in the sapwood, which in turn was negatively related to the degree of structural failure in the sapwood, associated with decay fungi. Carbon respiration was positively related to sapwood structural failure and we believe that the two insect groups act in concert to suppress wood decomposition in this system. This is contrary to prevailing wisdom among forest practitioners who have suspected that decay and insect activity are positively correlated, but in agreement with laboratory studies showing antagonism between stain and decay fungi. Lastly, we observed that neither forest harvesting nor fire had strong effects on the development of exemplar taxa from decay communities in ponderosa pine two years post-treatment. Though time since treatment did affect all functional groups inside of logs, only undisturbed old-growth treatments showed a reduced variability in composition, leading us to suspect effects to emerge at longer time intervals. / Graduation date: 2004

No description available.

Fusarium subglutinans sensu lato is a complex of fungi, which are the causal agents of important diseases on a wide variety of plants. Two important diseases caused by F. subglutinans sensu lato are pitch canker and mango malformation. F. subglutinans sensu lato isolates causing pitch canker on pine trees have been described as a separate species, F. circinatum. whereas F. subglutinans sensu lato isolates associated with mango malformation have not been formally described. The objective of study was to clarify the taxonomy and population genetics of the pitch canker and mango malformation fungi residing in the Gibberellafujikuroi complex. The introductory chapter of this thesis provides a review of the taxonomic classifications used for Fusarium spp. in the G. fujikuroi complex. In addition, the current knowledge pertaining to the population structure of the pitch canker and mango malformation fungi is discussed. In the second chapter the occurrence of F. circinatum was investigated in Mexico. Fusarium isolates were collected from pine trees in Mexico and identified as F. circinatum. Morphology, sexual compatibility studies, pathogenicity tests and histone H3-RFLPs were used to identify and characterize this fungus. The pitch canker fungus, F. circinatum and its teleomorph, G. circinata has been recently described. However, the name G. circinata is invalid, because insufficient information was provided to characterize the type specimen in the description. Additional information and a selection of F. circinatum isolates were, therefore, obtained and studies were undertaken in order to validate the description of G. circinata. The teleomorph G. circinata was validated and morphological criteria were shown to clearly distinguish F. circinatum from other F. subglutinans sensu lato isolates. Chapter four presents a study aimed at better understanding relationships between populations of F. circinatum from different geographical areas. For this study co¬dominant molecular markers were developed. These were then used to determine the genetic diversity, genetic distance and migration between different F. circinatum populations. Analysis revealed a high diversity in the Florida population and a low diversity in the South African population. Genetic analysis also indicated that the South African F. circinatum population originated in Mexico. In chapter five, the influence of sexual reproduction on the F. circinatum populations sampled over ten years in South Africa were studied. Sexual compatibility, vegetative compatibility and allelic diversity that were determined using polymorphic markers, developed in chapter four, were used. These results suggested that sexual reproduction is occurring more frequently in the more recently collected populations than in the initial population. Mango malformation is an important disease in mango growing areas. The study presented in chapter six indicated that this disease is associated with two distinct Fusarium spp. in the section Liseola. The two new Fusarium spp. are thus described as F. mangiferae and F. sterilihyphosum using morphological criteria In chapter seven, the distribution and vegetative compatibility of both F. mangiferae and F. sterilihyphosum was determined for the South Africa populations. Results revealed that each of these species differ in their distribution in South Africa. Vegetative compatibility tests also suggest that both species represent single genets in South Africa. Fusarium subglutinans sensu lato isolates associated with pme and mango are economically important fungi. The focus of the studies presented in this thesis has been on the taxonomy and population genetics of these fungi, with special reference to their occurrence in South Africa. Each of the chapters will contributes towards a better understanding of the taxonomy, population genetics and biology of these fungi. / Thesis (PhD)--University of Pretoria, 2006. / Microbiology and Plant Pathology / Unrestricted

Twenty sample plots located in Inonotus tomentosus (Fr.) Teng centers in mixed lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) and interior spruce (Picea glauca x engelmannii Engelm.) stands in central British Columbia were studied to investigate the behaviour of, and variation in host species attacked by the pathogen. The effect of infection on the radial increment of spruce and pine was studied by measuring increment bores. Characteristics of the fungus in culture were studied using isolates obtained from each of the study plots. In some cases, the fungus was found to behave differently on spruce and pine. In pine, advanced necrosis of the cambium and phloem of the roots caused crown thinning and eventual standing mortality. In spruce, decay of the heartwood and inner xylem of the roots caused windfall of the tree, often before expression of noticeable crown symptoms. In both host species studied, spread was commonly observed from infected to healthy, contacting roots. Possible cases of spore inoculation through root wounds were also found. In all plots, pine showed a higher infection level than spruce. Subalpine fir (Abies lasiocarpa (Hook.) Nutt.) and Douglas-fir (Pseudotsuqa menziesii (Mirb.) Franco) present within the plots were not found to be infected. Infection by I. tomentosus was not found to reduce significantly the basal area increment in pine or spruce. The fungus in culture demonstrated a large amount of variation in growth rate, mycelium color and mat color and texture. Such variation occurred both within and among isolates, and could not be related to the host species from which the isolate was obtained. / Forestry, Faculty of / Graduate

No description available.

Ovariole development and termination of diapause in the white pine weevil were studied by dissecting weevils at various intervals throughout the winter. Old-generation adults brought into the laboratory November produced viable eggs within 5 days. New generation adults brought into the laboratory on November 4 produced viable eggs during November. Viable eggs were deposited by other new-generation adults after 10 to 15 day. at room temperature in winter. On each of the 3 collection date studied, new generation adult produced viable eggs without copulating after collection from hibernation indicating that capulation occurs in the fall. There was no evidence of progressive ovariole development throughout the winter. New generation adults which were isolated as soon as they emerged from the shoots and maintained at constant room temperature had poorly developed ovarioles by November 20 and produced no eggs. Weevil flight and dispersal through a white pine plantation was studied by releasing 409 marked weevils at a central point within a l431-tree plantation and checking every tree at 5-day intervals. Weevils flew readily at the time of re1ease. Marked weevils were recorded throughout the plantation. which extended as far as 330 feet from the release point. A few weevils were observed on scattered white pines 200-300 yards from the release point beyond a hardwood barrier. Total numbers of weevils present on the leaders increased from April 26 to May 5, after which numbers steadily decreased. By June 15, only 20 weevils were observed on the leaders. / Ph. D.

Procerum root disease of eastern white pine (Pinus strobus L.), caused by Leptographium procerum (Kendr.) Wingf., has been epidemic in Virginia Christmas tree plantations since 1990. Symptoms of chlorosis, wilt, and decreased apical growth resemble those of water stress. Resin infiltration of the xylem at the stem base may be responsible for vascular occlusion leading to severe water deficits and mortality. The pathogen has been isolated from the roots of ozone-sensitive eastern white pines in the field, although not from nearby tolerant trees, and it may be that ozone sensitivity predisposes the trees to infection. The objectives of my Studies were to investigate the physiology of diseased white pines, and to determine the effects of ozone fumigation on disease development. Impacts of vascular occlusion upon host water relations and gas exchange were investigated in 8-yr-old, plantation-grown, white pine Christmas trees. Disease severity was estimated as the proportion of resin-soaked cross-sectional area at the base of the stem. The linear response of a suite of six physiological variables to disease severity was highly significant. Individually, the variables pre-dawn water potential, daily change in pre-dawn to mid-day water potential, stomatal conductance, and photosynthetic and transpiration rates all decreased significantly with increasing disease severity. Fumigation studies were conducted on white and loblolly (P. taeda L.) pine seedlings to determine if ozone exposure increased the incidence of root disease or the amount of stem tissue colonized by L. procerum. Roots were inoculated by soil drenching with conidial suspension, and stems were wounded at the base and inoculated with mycelium. Beginning 24 h post-inoculation, and for 14 consecutive days, seedlings were fumigated in closed chambers with charcoal-filtered air or 200 ppb ozone for 5 h/day, then removed to a charcoal-filtered greenhouse. Six weeks post-inoculation, root and stem tissue were plated on a medium selective for L. procerum. Ozone treatment did not significantly affect the proportion of diseased roots per seedling or the vertical colonization of stem tissue in seedlings of either species. / Ph. D.

The hypothesis that stressed loblolly pine (Pinus taeda L.) could be distinguished from non-stressed loblolly pine by increased foliage temperatures was tested. The foliage temperatures of seedlings and trees were measured with an AGA Thermovision 680 system, imported by the AGA Corporation, Secaucus, New Jersey. The AGA Thermovision 680 system is a simple, easily transported remote sensing system for detecting relative apparent temperatures of plant foliage without direct contact with the leaves. This system is sensitive to infrared wavelengths in the 2-5.6 micron region of the electro-magnetic spectrum. Foliage temperatures in loblolly pine seedlings increased within one week of stress induced by drought, flooding, or severing. Increased temperatures of stressed seedlings were associated with reduced needle moisture content prior to visual symptoms of stress. Foliage temperatures of loblolly pine trees stressed by severing the bole were warmer relative to neighboring control trees. Increased temperatures were detected within one week after severing. Previsual detection of stress can be achieved by measuring foliage temperatures of loblolly pine. The AGA Thermovision should prove to be a useful tool for non-destructive sampling of plant stress, for locating stressed trees, and potential bark beetle infestations. / Ph. D.