Abstract: Three bacterium strains with a high frequency,viz.Njh,Njt and Njw,have been isolated from the xylem of a wilted black pine( Pinus thuntergii )tree caused by pine wood nematodes and from the surface of the nematodes.These bacteria have been identified as Pseudomonas fluorescens biotype I, Pseudomonas fluorescens biotype II and a species of the genus Pantoea respectively.Bacteria were cultured in liquid media through rocking.The liquid was directly used in the treatment of the callus of black pine and ability of each kind of bacterium to produce toxin was measured.As compared with control(viz.blank liquid media),the original culture liquid from three kinds of bacteria had an obvious effect on wilting of the materials used in bioassay.Strains Njh and Njt were stronger than Njw in pathogenicity.Part of calluses turn yellow browning 48 hours after the original liquid containing toxin was added.5 days after bioassay all of the callus masses were black browning and died on account of the original liquid containing the toxin from strains Njh and Njt added.There was no big change in color of the callus to which the liquid containing the toxin from the strain Njw was added,but it’s darker than the control.It has been proved that there was a great quantity of wilt related toxins existing in strains Njh and Njt