Development of Heterobasidion spp. fruit bodies on decayed Piecea abies

Because intensive forestry favors the spread of Heterobasidion spp., increasing amounts of decayed Norway spruce (Picea abies) wood in forest stands should be taken into account in the management of commercial forests. Spruce wood colonized by Heterobasidion spp. ensures fruit body formation, which increases the risk of new infections by basidiospores and, subsequently, the spread of Heterobasidion root rot. To date, very little is known about the prevalence of Heterobasidion fruit bodies on decayed spruce wood in different environments. To assess Heterobasidion fruit body production on various soil types and on different parts of trees, more than 36,000 fruit bodies on 425 decayed logs, 321 decayed trees, and 262 stumps of Norway spruce located on mineral and peat soils were surveyed. The most abundant fruit body formation occurred on infected spruce logs left on peat soil. Significantly more fruit bodies (average total fruit body area cm² m⁻³) were found on logs on drained peat soil compared to drained mineral soil (4960 and 2674 cm², respectively). On stems of windthrown, uprooted trees, approximately three times more actively sporulating fruit bodies were formed compared to roots. Further, approximately two times more Heterobasidion fruit bodies occurred on the roots of partly uplifted stumps than on stumps with roots remaining in the soil. H. parviporum was identified in 88% and H. annosum in 12% of analyzed spruce individuals. In cases where the tree was infected by H. annosum s.s., fruit bodies of this fungus were also commonly produced on spruce wood. Abundant development of fruit bodies was also observed in abandoned agricultural and pasture lands. Moreover, rich vegetation in fertile forest types favored fruit body development on both mineral and peat soils. On such sites, infected logs and windthrown trees, as well as partly uplifted spruce stumps, should be removed to limit the spread of Heterobasidion spp. by basidiospores.