Heterobasidion annosum s.l. is a serious forest pathogen that causes significant economic losses, especially in the Northern Hemisphere. In Finland, the H. annosum s.s. and H. parviporum within the Heterobasidion complex affect the growth and wood properties of Norway spruce (Picea abies (L.) Karst.) and its suitability for different industrial purposes. The main aim of this PhD thesis was to study the wood degradation (WD) caused by H. annosum s.l. and enzymatic hydrolysis under laboratory conditions in wood specimens representing different genotypes and crown types of Norway spruce, and at positions along the stem. Furthermore, the relationship between WD and different traits such as tree growth, physical properties and wood chemical composition, as well as the production of reducing sugars (RS), were also studied.
The WD differed between normal-crowned Norway spruce clones, but not between normal- and narrow-crowned trees. H. annosum s.s. caused a higher WD than H. parviporum. The WD was also affected by the position within the wood discs, along the stem and by the age of the sample trees. In older trees, samples taken near the pith were more degraded than those taken near the bark and vice versa. In younger trees, wood density correlated negatively with WD. Positive correlations were also observed between RS and WD, suggesting that genotypes susceptible to WD may represent desired raw material for some other industries in which the hydrolysis of the main wood components is essential (i.e., biorefining). To conclude, this thesis showed that the genotypic variation observed in breeding material may represent an advantage for forest tree breeding to control and avoid Heterobasidion attacks, especially when studied along with other important traits and considering silvicultural practices such as the thinning regime and rotation length that may affect WD risk by H. annosum.