Efficacy of Phlebiopsis gigantea against Heterobasidion conidiospore and basidiospore infection in spruce wood

Treatment of freshly cut stumps with biological control agents containing Phlebiopsis gigantea spores effectively restricts the spread of new Heterobasidion infections in conifer forests. To test the control efficacy of different P. gigantea strains, conifer stumps or billets cut from tree stems can be artificially infected with asexual Heterobasidion conidiospores or sexual basidiospores or left for natural basidiospore infection. Currently, no information is available about whether the control efficiency of P. gigantea in Norway spruce wood is affected by Heterobasidion spore type. In the present study, the impact of four P. gigantea strains (including the commercial product Rotstop (R)) on initiation and development of Heterobasidion basidiospore and conidiospore infections as well as the relationship between the area occupied by P. gigantea and control efficacy were analysed in spruce billets. The mean size of the area occupied by P. gigantea was larger, and the efficacy of P. gigantea against Heterobasidion was significantly higher in billets left for natural basidiospore infection compared to treatment with Heterobasidion conidiospore suspension. The control efficacy against Heterobasidion infection was high, although only a small area of the billet surface was occupied by P. gigantea and even when there was no visible discoloration caused by P. gigantea infection on wood surfaces.