PROBLEM TO BE SOLVED: To provide a technique that is directly applicable to causal fungus of white root-rot inhabiting the outdoor environment, the technique enabling the desired mycovirus to arbitrary causal fungus of white root-rot irrespective of mycelium compatibility.SOLUTION: According to the present invention, there is provided a causal fungus of white root-rot having the following mycological properties (1) to (4): (1) the property that hyphae cultured on a PDA medium at 25°C has conidiogenic ability without forming any conidiophore bundle； (2) the property of cytoplasmic fusion to the mycelial cells of other causal fungus of white root-rot via conidia regardless of mycelium compatibility； (3) the property of allowing the retained mycovirus to be transferred to the mycelial cells of another causal fungus of white root-rot mycelium via the cytoplasmic fusion described in the above (2)； and (4) the property of containing in genomic DNA a nucleotide sequence that shows 95% or more identity with a nucleotide sequence as a region between 18S rDNA and 28S rDNA or as a region included in such a region.SELECTED DRAWING: Figure 7【課題】所望のマイコウイルスを菌糸体和合性に関わらずに任意の白紋羽病菌に移行可能とする技術であって、野外環境に生息する白紋羽病菌に対して直接使用可能な技術を提供する。【解決手段】下記（１）～（４）に記載の菌学的性質を有することを特徴とする白紋羽病菌、（１）ＰＤＡ培地上で２５℃にて培養した菌糸が分生子柄束を形成することなく分生子形成能を有する性質、（２）他の白紋羽病菌の菌糸細胞に対して、菌糸体和合性に関わらずに分生子を介して細胞質融合する性質、（３）上記（２）に記載の細胞質融合を介して保持しているマイコウイルスを他の白紋羽病菌の菌糸細胞に移行可能な性質、（４）１８ＳｒＤＮＡ及び２８ＳｒＤＮＡ間の領域として又は当該領域に含まれる領域としての塩基配列と９５％以上の同一性を示す塩基配列、をゲノムＤＮＡ内に含んでなる性質。【選択図】図７
