Heterobasidion annosum (Fr.:Fr.) Bref. is one of the most widespread and damaging root and butt rot agents on conifers. In the summer of 1998, H. annosum was observed for the first time on the Swiss Stone Pine (Pinus cembra L.) in its natural range (1) at 1,900 m in the Aosta Valley in the northwestern Italian Alps. The affected tree was 14 m tall and about 60 years old. It was growing in a mixed spruce (Picea) and larch (Larix) forest severely affected by H. annosum. There were no clear crown symptoms but, after felling, an extensive butt rot was noticed up to 4 m from the collar. The pathogen was isolated from a disk cut at a height of about 40 cm. Its anamorphic form (Spiniger meineckellum (A. Olson) Stalpers) developed on this disk after 8 days of incubation at 20°C. H. annosum was also isolated from the central cylinder of the tree's primary roots and on the other roots down to a diameter of 0.5 cm. Sexual mating tests with single-spore testers for the P, S, and F intersterile groups (ISGs) showed that the isolate belonged to S-ISG. Biomolecular tests on this strain are in progress to confirm this.
Reference: (1) T. G. Tutin et al. 1993. Flora Europaea. Cambridge University Press, Cambridge.
