This award will support collaborative research in systematic biology between Dr. Everett Hansen, Oregon State University and Drs. Jan Stelid and Martin Johansson, Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden. The objective of the project is to study the population genetics of root disease fungi of coniferous trees, and particularly the mechanisms of vegetative P compatibility. Individuals of many fungus species maintain their separate identity by a vegetative compatibility (VC) system that prevents exchange of nuclei and cytoplasm. The phenomenon is readily demonstrated in Heterobasidion annosum, cause of annosus root rot in forest trees. VC reactions are used in studies of population genetics and the introduction of debilitating viruses into fungus populations. Interpretation is hampered, however, by lack of information on the physiology and genetic regulation of the VC reaction. The main objectives of the proposed project are: 1) to describe the physiological and anatomical reactions of interacting vegetatively compatible and incompatible dikaryotic mycelia of H.annosum; and 2) to determine the system of genetic control of VC in this fungus. Interactions between genetically defined mycelia will be observed in microculture chambers and responses of cytoplasm, nuclei, and mitochondria will be visualized with appropriate histological techniques. Exchange of nuclei and cytoplasm will be monitored using isozyme and drug resistance markers. Protein products of the interaction will be determined by electrophoresis. Genetic control of VC will be assessed by pairing and backcrossing sib-composed heterkaryons, with the goal of determining the number of genes that control this reaction. H.annosum is presently causing tremendous damage, especially in Europe, and all indications are that it will be more destructive in the future. Further understanding of its biology will be of significant value to forest pathologists in both Europe and North America.
