Abstract

The present thesis summarizes and concludes the work of four separate studies on Heterobasidion annosum (Fr.) Bref. s.l.. The basic aim of these studies was to provide a tool for investigation and cloning of genetic regions in H. annosum s.l. and apply this tool to different regions of interest. The progeny isolates of a cross between North American intersterility groups S and P were used in an inoculation experiment on two-week-old Pinus sylvestris and demonstrated the nuclear contribution to be important for virulence. From the same population, a genetic linkage map was constructed based on 358 AFLP markers, consisting of 19 larger and 20 smaller linkage groups (LG). Based on further virulence tests on both one-year-old Pinus sylvestris and two-year-old Picea abies, several regions controlling virulence were identified and mapped to these LG. In particular, LG 15 was of interest, containing QTLs for pathogenicity to both pine and spruce. The tests also indicated that hybridization negatively affects virulence. An investigation of somatic incompatibility was conducted, using two heterokaryotic populations made from the progeny, backcrossed with a parental strain or crossed with an unrelated strain. The number of incompatibility loci was estimated to four and it was shown that the allelic differences alone are not enough to determine the degree of the incompatibility reaction. Furthermore, several strong QTLs for different intraspecific interactions that may be important to the incompatibility phenomenon were located. Future work includes map based cloning and investigation of the QTLs identified in this thesis; a task that will benefit substantially from the upcoming sequencing of the H. annosum s.l. genome.