Abstract: In order to search for new microbial resources to antagonize Valsa canker of apple，a potential biocontrol strain was isolated and purified from the phloem tissue by a flat-panel test in this study. The strain was identified based on its colony，strain morphology，16S rDNA and gyrA gene sequence. The strain was identified as a Bacillus amyloliquefaciens，named as BaA-007（Agricultural Culture Collection of China，preservation number：ACCC60382）. We further confirmed the strong antifungal activity of the strain and its secondary metabolism to Valsa mali. Results showed the strain and its secondary metabolites could inhibit the growth of Valsa mali，and significantly reduced the spread rate of the rot spots. Based on BG medium，the best cultural condition was 0.5% sucrose，1% bacteriological peptone，0.1% potassium dihydrogen sulfate，pH 7.0 and temperature 36 ℃. After inoculation of BaA-007，the salicylic acid（SA）- responsive genes PR1，PR2 and NPR1，the jasmonic acid（JA）-responsive genes PDF1.2，CORONATINE INSENSITIVE 1（COI1）and AOS，the ethylene（ET）-responsive genes ETR1，ERF1 and HEL，as well as Chitin synthetase B genes were all upregulated at different points. Above all，the strain BaA-007 had a good antagonistic effect on Valsa canker，and it was expected to be used as a biocontrol strain to prevent apple Valsa canker.

Key words: apple, apple Valsa canker, biological control, Bacillus amyloliquefaciens, culture condition screening, inhibition mechanism