Abstract: The aim of this study is to screen bacteria with efficient nematicidal activity against Bursaphelenchus xylophilus. Immersion test was to assess the nematicidal activities of 3 Bacillus strains,then the morphological depiction on the polypides of nematodes killed by fermentation filtrate of the selected efficient strains were observed,as well as the culture condition and the stability of substances with nematicidal activity were also determined. The results revealed that the corrected mortality of nematodes was 100% after B. xylophilus were treated for 48 h with fermentation filtrate by 3 bacteria strains. The corrected mortality of nematodes was still up to 99.55% and 88.32%,respectively when they were treated for 48 h with B. cereus JK-XZ3 in fermentation filtrate diluted for 4 times and 8 times. It was significantly higher than the corrected mortality of nematodes treated with B. pumilus HR10 and B. velezensis YH-20 fermented filtrate. Moreover,the polypides of nematodes treated with the fermentation filtrate of JK-XZ3 were broken,and contents overflowed,and body wall was dissolved. The filtrate of JK-XZ3 fermented in 30℃ for 4d presented the highest nematicidal activity,and the corrected mortality of nematodes,when treated for 48h with the fermentation filtrate diluted for 4 and 8 times,were both up to 100%,respectively;the corrected mortality of nematodes was more than 84% when the nematodes were treated for 48 h in the 8 times-diluted fermentation filtrate processed at 40、60、80 and 100℃;at pH of 8-10,the corrected mortality of nematodes was > 88% when they were treated for 48 h in 8 times-diluted fermentation filtrate. It indicated that the fermentation filtrate of the strain demonstrated the characteristics of high temperature and alkali resistances. B. cereus JK-XZ3 is a highly virulent nematicidal strain with potentials of research and application.

Key words: Bursaphelenchus xylophilus, Bacillus cereus, fermentation filtrate, nematicidalactivity