An examination of genetic variation and disease spread in Inonotus tomentosus in the sub-boreal spruce zone of British Columbia.

Inonotus tomentosus (Fr) Teng. is a fungal pathogen of commercially valuable tree species in British Columbia and one of the most important biotic disturbance agents in sub-boreal and boreal forests in Canada. This study investigated the population variation in six spruce stands infected with Tomentosus Root Rot (TRR) in order to determine whether infection is due to spread by root contact, by basidiospores, or a combination of the two and if forest management affects the mode of disease spread. Three marker types were used to test for variation in populations. These included vegetative compatibility (VC), random amplified polymorphic DNA (RAPDs) and single strand conformation polymorphisms (SSCP). Genetic and genotypic variation as well as linkage disequilibrium and random mating were measured. There is high genotypic variation within all populations in addition to moderate levels of gene diversity, significant linkage disequilibrium and significant deviation from Hardy- Weinberg Equilibrium. Analysis of Molecular Variance (AMOVA) indicated that 70% of genetic variation occurred within populations and 28% occurred between populations. This indicates that some clonal propagation is occurring in these populations but frequent recombination (i.e. sexual reproduction) and subsequent spore dispersal (although spatially limited) is the most likely cause of the high level of genotypic diversity observed in these sites. There was no apparent difference in the population structure of this pathogen between unmanaged mixed-species stands and spruce plantations. Given this information, the current management guidelines for treating sites affected by TRR may be insufficient because many of them are aimed at interfering with spread by root contacts.