Evaluation of Soil Antagonism against the White Root Rot Fungus Rosellinia necatrix and Pathogen Mycosphere Communities in Biochar-amended Soil.

White root rot disease caused by Rosellinia necatrix is a growing issue in orchards, and biochar pyrolyzed from the pruned branch residues of fruit trees has potential as a soil amendment agent with a number of benefits, such as long-term carbon sequestration. However, the effects of pruned branch biochar on white root rot disease remain unclear. Therefore, we compared direct antagonism against R. necatrix between soils with and without pruned pear branch biochar using a toothpick method and then linked soil physicochemical properties and microbial communities with soil antagonism. The results obtained showed that soil antagonism against the pathogen, that is, the extinction zone of R. necatrix in mycelial toothpicks, decreased in soils amended with 20% (v/v) pruned branch biochar. Soil pH was neutralized and aeration was promoted by the biochar amendment, which may be favorable for pathogen growth. An investigation of microbial communities surrounding R. necatrix mycelia indicated that antagonistic fungi affiliated with Chaetomiaceae and Trichoderma were selectively excluded from the mycosphere community in biochar-amended soil. Therefore, the enrichment of these indigenous antagonistic fungi may be important for controlling R. necatrix. Based on the present results, we do not recommend the application of pruned branch biochar to the soil area associated with the roots of fruit trees in order to avoid increasing the risk of white root rot in orchards.