In the western regions of North America, mountain pine beetle, Dendroctonus ponderosae Hopk., infestations take a tremendous toll of pines , especially lodgepole pine, Pinus contorta Dougl. var. latifolia Engelm.. Mass attack by the beetles is a devastating event for the trees. As well as girdling the tree, a massive inoculation of blue stain fungus "complex" (composed of several species of Ceratocystis, numerous yeasts and other mycelial fungi) is made beneath the bark. These fungi colonize and destroy the parenchyma tissue system of the host sapwood, primarily the ray parenchyma and resin duct epithelium. A blue stain is produced in the sapwood as a consequence of destruction of the sapwood parenchyma. The stain develops inward through the sapwood, and the transpiration stream is cut off. As more and more sapwood is stained, foliar water stress begins to increase. Foliage however, remains green and apparently healthy for up to 10 months after inoculation. When spring bud break begins the year following beetle attack, terminal buds of blue-stained trees begin to expand, then abort. Soon after, the needles of these trees fade to a reddish brown color. Transpiration stream disruption was not caused by penetration of tracheids by fungal hyphae; tyloses were not observed; nor was microconidial blockage of bordered pits seen. Though resin duct epithelium was eventually destroyed, little resin soaking was observed in the initial blue stained regions. Many bordered pits of tracheids in stained regions appeared to be aspirated, suggesting introduction of embolisms.

Bark beetles regulate forest succession by removing weakened or stressed trees and exposing understory species to light from canopy gaps. Subterranean termites are predominate decomposers of coarse woody debris in southern pine forests; however, little is known about their role in forest health and succession. Both groups of insects rely heavily on fungal symbioses to fill their respective ecological niches in southern pine forests. During recent inspections of southern pine timber, we observed that trees in the early stages of bark beetle attack often had subterranean termites in blue-stained portions of the trunk. The frequency of subterranean termite presence in blue-stained areas of trees increased proportionally to the stage of bark beetle attack. However, practically no research has undertaken the challenge of describing how woody resources created by bark beetles are identified and utilized by subterranean termites before any signs of stress are visible. Therefore, this study examined possible facilitative interactions between subterranean termites, bark beetles and their blue-stain fungal associates, and other invertebrates, and investigated the effect of blue-stain fungi on surface properties of wood. Both native (Reticulitermes spp.) and Formosan subterranean termites exhibited a higher feeding preference for blue-stained sapwood than for unstained sapwood in laboratory assays. Native subterranean termites also consumed blue-stained sapwood at a higher rate than decayed wood. This study was the first to demonstrate that wood containing a non-decay fungus could elicit a feeding response from subterranean termites greater than that observed for decayed wood. Additionally, the surface properties of bark beetle-attacked southern pine were initially reduced by blue-stain fungal infection; however, the process of kiln-drying reversed this effect, resulting in a surface that was more conducive to wood product manufacturing.

This work presents a survey of blue-stain fungi found in Northwestern Ontario, characterization of a homing endonuclease gene within Grosmannia piceiperda and finally an examination of the introns and homing endonuclease genes found in the large ribosomal subunit gene in species of Ceratocystis; using molecular techniques and phylogenetic analysis, we studied the molecular evolution of these mobile genetic elements. The blue-stain fungi of Northwestern Ontario were identified based on phylogenic analysis of rDNA internal transcribed spacer region sequences. This data was supplemented with morphological characteristics of the fungal cultures. The second project was an examination of a LAGLIDADG homing endonuclease and its IC2 group I intron. This intron is uniquely positioned within the group I intron-encoded rps3 gene of the large subunit ribosomal RNA gene. The final chapter is an investigation of the large subunit ribosomal RNA gene in species of Ceratocystis. The 3’ segment of this gene contains several novel introns and homing endonuclease genes. There is also much diversity between strains despite their close relation on the rDNA internal transcribed spacer region phylogenetic tree. Further, our data also suggest that the single motif LAGLIDADG homing endonuclease of the rDNA mL1923 intron is likely to be an ancestor to other homing endonucleases in the area. The results of these studies demonstrate the role that these elements play in the genetic diversity observed in the blue-stain fungi.

This work presents a survey of blue-stain fungi found in Northwestern Ontario, characterization of a homing endonuclease gene within Grosmannia piceiperda and finally an examination of the introns and homing endonuclease genes found in the large ribosomal subunit gene in species of Ceratocystis; using molecular techniques and phylogenetic analysis, we studied the molecular evolution of these mobile genetic elements. The blue-stain fungi of Northwestern Ontario were identified based on phylogenic analysis of rDNA internal transcribed spacer region sequences. This data was supplemented with morphological characteristics of the fungal cultures. The second project was an examination of a LAGLIDADG homing endonuclease and its IC2 group I intron. This intron is uniquely positioned within the group I intron-encoded rps3 gene of the large subunit ribosomal RNA gene. The final chapter is an investigation of the large subunit ribosomal RNA gene in species of Ceratocystis. The 3’ segment of this gene contains several novel introns and homing endonuclease genes. There is also much diversity between strains despite their close relation on the rDNA internal transcribed spacer region phylogenetic tree. Further, our data also suggest that the single motif LAGLIDADG homing endonuclease of the rDNA mL1923 intron is likely to be an ancestor to other homing endonucleases in the area. The results of these studies demonstrate the role that these elements play in the genetic diversity observed in the blue-stain fungi.

農林水産研究情報センターで作成したPDFファイルを使用している。