The impacts of treatment with biocontrol fungus (Phlebiopsis gigantea) on bacterial biota of Norway spruces stumps. Pg effect

The biocontrol agent Phlebiopsis gigantea has been intensively applied on the surface of Picea abies stumps against Heterobasidion root rot. However, very little is known on the possible impact of such treatment on the resident bacteria community in the stumps. We have for the first time used high throughput DNA bar-coded pyrosequencing to characterize the diversity as well as the successional dynamics of bacteria in the stumps of P. abies after 1-, 6- and 13-year post treatment with P. gigantea. The sequences were classified into 12 bacterial phyla and 160 genera, in which Proteobacteria and Acidobacteria were the most abundant groups in the stumps. Successionally, Proteobacteria were the most abundant at the initial stages of stump decay but were selectively replaced by Acidobacteria at advanced stages of the decay. Treatment with P. gigantea led to significant increase of the genus GP1after 1-year treatment. The analysis of observed and estimated operational taxonomic units (OTUs) as well as diversity indices revealed that P. gigantea treatment significantly decreased the bacterial richness at initial decay stage in the stumps. Over time, the bacterial community in the stumps gradually recovered and the negative effects of P. gigantea was attenuated. These results provide additional insight on the risk assessment as well as environmental impact on the long-term use of P. gigantea in the control of Heterobasidion root rot in conifer forests.