Abstract: Bacillus sp. SM905 isolated in our previous study is a bacterium with antifungal activity. In this study, strain SM905 was further identified as B. velezensis based on its morphological and physiological characters combined with the sequences analysis of 16S rDNA and gyrB. Mycelial growth rate assay showed that mycelia growth of C. gloeosporioides was inhibited in varying degrees by different dilutions of SM905 fermentation supernatant. Fermentation supernatant diluted five times exhibited the highest inhibition activity against mycelial growth with the inhibition rate of 97.89%. Cover glass insertion cultivation assay indicated that the aerial mycelium of C. gloeosporioides treated with the fermentation supernatant showed abnormal morphology, such as vesicular deformities and pigment accumulation, and that a large amount of conidia were produced from the substrate mycelium. The results of the agar plate cultivation showed that strain SM905 fermentation supernatant treatment had little effect on the conidia germination rate of C. gloeosporioides, however, the newly formed mycelium grew slowly with the swelling morphology. In the pot experiments, 100-fold diluted SM905 powder was sprayed twice with an interval of 7 days, and the control efficacy on Dendrobium officinale anthracnose reached 80.74%, which was higher than that of treatment of 10% Difenoconazole WDG (800X dilution). Over all, our study indicated that B. velezensis strain SM905 is a promising bioagent used in biocontrol of D. officinale anthracnose.

Key words: Colletotrichum gloeosporioides, Dendrobium officinale, Bacillus velezensis, identification, antifungal activity