巨大芽胞杆菌（Bacillus megaterium，Bm）的抑菌活性及定殖规律分析

为进一步明确巨大芽胞杆菌（Bacillus megaterium，Bm）菌株对烟草主要病害的抑制效果，利用半叶法、对峙平板法和抑菌圈法研究了Bm对烟草花叶病毒（TMV）、黑胫病菌和青枯病菌的抑制作用；利用抗生素诱导筛选抗药性标记菌株，研究其在烟草根际土壤和叶面上的定殖规律；同时制备了生防菌发酵液制剂，测定其田间防治效果。结果表明:Bm发酵液和发酵上清液对烟草花叶病毒的抑制率分别为88.4%和74.3%；Bm无菌发酵上清液对黑胫病菌菌丝生长的抑制率为67.5%，对青枯病菌的抑菌圈直径为10.03 mm。抗药性菌株Bm-rif生长性状与野生型无差异。室内定殖试验结果显示，Bm-rif稳定定殖菌量在非灭菌土壤中为0.04×105 cfu/g，在灭菌土壤中为0.47×105 cfu/g，均显著高于叶面定殖菌量；接种TMV-GFP前24 h叶面喷施发酵液对TMV初侵染的抑制率为44.04%。菌株发酵液稀释后喷淋烟株茎基部，对烟草黑胫病和青枯病的田间防治效果分别为68.09%和51.02%。因此，Bm具有抑菌活性且能在烟草根际土壤中有效定殖，具有开发为生防菌剂的潜力。 

Antibacterial activity of Bacillus megaterium strain Bm and its colonization laws

To further clarify the inhibitory effect of Bacillus megaterium strain Bm on main tobacco diseases, the inhibiting effects of BM on tobacco mosaic virus(TMV), Phytophthora parasitica var. nicotianae and Ralstonia solanacearum were studied by the half-leaf, plate confrontation and inhibition zone methods, respectively. A strain with resistance to antibiotic was screened out with rifampicin, and its colonization laws in tobacco rhizosphere soil and on tobacco leaves were analyzed. Bio-control bacterium fermented broth was prepared and its field control effect was determined. The results showed that the inhibition rates of Bm fermented broth and its supernatant on TMV were 88.4% and 74.3% respectively, and the inhibition rate of the fermentation supernatant on the mycelia of Phytophthora parasitica var. nicotianae was 67.5% and the diameter of inhibition zone of Ralstonia solanacoarum in culture plate was 10.03 mm. There was no difference in growth traits between the resistant strain Bm-rifand the wild-type strain. The results of colonization experiments in greenhouse indicated that the population of stably colonized Bm-rif was 0.04×105 cfu/g in soil without sterilization and 0.47×105 cfu/g in sterilized soil, which were all significantly higher than those on tobacco leaves. Twenty-four hours before the TMV-GFP inoculation, the inhibition rate of foliage spray using the fermentation broth on primary infection of TMV was 44.04%. The field control effects of a diluted fermentation broth sprayed at the basal part of tobacco stalk against Phytophthora parasitica var. nicotianae and Ralstonia solanacearum were 68.09% and 51.02%, respectively. Therefore, Bm has antibacterial activity and can effectively colonize in tobacco rhizosphere soil, and has the potential to be an antibiological inoculant.