Wood decay caused by Heterobasidion parviporum in juvenile wood specimens from normal- and narrow-crowned Norway spruce

Heterobasidion parviporum (Fr.) Niemelä & Korhonen is a serious forest pathogen affecting the quality of Norway spruce (Picea abies (L.) Karst), especially in northern hemisphere. Here, we studied the wood decay caused by this pathogen in small wood specimens of 19-year-old normal (P. abies) and narrow crowned (P. abies f. pendula) Norway spruce trees. After six months of incubation, wood specimens taken next to pith (inner) and bark (outer) at 1 m height from the stem base were measured to obtain the percent dry weight loss. The fungal development was also analyzed using Scanning Electron Microscopy (SEM). We found that the crown type (or genetic entry) had no effects on the weight loss. However, outer wood specimens lost, on average, more weight than inner ones. Similarly, wood density and content of lignans were lower at outer sections, opposite to the free glucose content. Wood density correlated negatively with the weight loss of wood specimens, regardless of crown type. Considering that narrow- and normal-crowned trees responded similarly to H. parviporum wood decay, our findings support the potential use of narrow-crowned Norway spruce in practical forestry since they can produce higher stem yield at very dense plantation and without thinning requirements.