Intraspecific variation in Heterobasidion annosum for growth in sapwood ofPicea abies and Pinus sylvestris

Two greenhouse experiments were conducted to study intraspecific variation in growth of the root rot fungus Heterobasidion annosum in living host sapw ood. In experiment i, Scots pine (Pinus sylvestris) and Norway spruce (Pice a abies) seedlings were inoculated with H. annosum isolates, 14 each of the Soups, collected from various parts of Sweden. In pine, the P-group isolat es were the S-group isolates both in terms of infection frequency, induced mortality rare (p < 0.05), and fungal grown th in sapwood (p < 0.05). In sp ruce, the P-group isolates were also more virulent on average, bur the diff erence was not statistically significant. Both S and P isolates had a highe r infection frequency and a significantly longer sapwood growth on spruce t han on pine. The P-group caused higher mortality on pine than on spruce. Th e length of the lesion in the inner bark was strongly correlated with funga l growth in spruce, but not in pine where the lesions were short or absent. In experiment 2, ten Nowray spruce clones were inoculated with 18 S-isolat es, originating from nine live-decayed trees from nine spore-infected stump s in a single Norway of H. annosum originating either from stumps or trees. The results gave no support for such selection since no difference in sapw ood growth between the two groups of isolates was found.