Browsing by Author "Stewart, Erik"

Heterobasidion annosum s.l. is a devastating forest pathogen species complex which causes extensive damage to timber products in northern Europe. This study examined resistance of Norway spruce (Picea abies) in two field sites in Finland to annosum root rot (Heterobasidion parviporum) utilizing non-clonal stocks of P. abies. The northern field site in Rovaniemi does not have a historical presence of the pathogen, whereas the southern field site in Lapinjärvi has extensive historical presence of the pathogen. The goals of the study were to assess potential difference in susceptibility between the sites, as well as to examine the differences in susceptibility between tissue types and organs in the trees examined. The study inoculated treatment trees with H. parviporum, as well as mock inoculations without the pathogen for control trees. Six inoculations of one treatment type were placed into each of thirty randomly selected trees at both field sites. Three inoculations were done in the stem, and three in the roots, for a total of 360 inoculations. After being left in situ for three months, the trees were harvested, and resulting lesions in the phloem and xylem tissues in both the roots and stem were measured to determine the extent of visible lesion extensions from the inoculation point. Data collected from the experiment was analyzed in the context of three mixed effects models, with the assumption that larger lesions indicated lower resistance to the pathogen. The measurements considered as response variables for the models were the total length of the lesion, total width of the lesion, and total area of the lesion. Results indicated minor overall differences in the lesion sizes between site in the lesion width and lesion area models. Significant differences were found between tissue types in the lesion width, and lesion area models. Additionally, interactions between treatment and organ, as well as treatment and tissue were significant across all models. Several other interactions were significant across some, but not all models The results indicate that further research into the potential effects of historical or geographic isolation on the resistance of P. abies to H. parviporum should include strict genetic controls with crossing of genotypes across sites, and should also consider the differences due to abiotic factors which may influence resistance in field trials.