Studies On Optimization Of Fermentation Conditions And Biocontrol Effects Against Ustilaginoidea Virens Of Bacillus Subtilis Xi-55

Bacillus subtilis strain Xi-55 is a biocontrol microbe isolated from rhizosphere of rice by biocontrol lab of Plant Protection Institute of Sichuan Academy of Agricultural Sciences.The earlier stage study results showed that the fermentation extracts had a high fungicidal activity against mycelium growth or spore germination of many plant pathogenic fungus.On the basis of studies of topic group,this dissertation is focused particularly on studies on fermentation condition optimization,test of antibiogram,test of stability of fermentation broth,control efficacy of Bacillus subtilis Xi-55 against rice false smut in the greenhouse and field.The main results are as follows:(1) By single factor experiment and orthogonal experiment,the liquid fermentation medium and technological conditions of Bacillus subtilis Xi-55 were optimized.The results showed that optimum medium formula was peptone 3%, glycerine 1.0%,K₂HPO₄ 0.05%,MgSO₄·7H₂O 0.15%.The favorable fermentation condition was determined:time 36h,temperature 28℃,initial pH value of medium 7, inoculation amount 2%,pack amount 100ml/500ml triangle bottle.The magnifying culture in 20L fermentation tank was conducted,the growth peak value appeared in 36h,optimum cultivating time 44～48h,and the obtained bacterium amount was up to 5 x 10⁹cfu/ml in fermentation liquid.(2)It is showed that the fermentation of Xi-55 is not stable to temperature,it can keep inhibition activity at 60℃and 80℃while the inhibition activity falls down at 100℃;it is stable in neutral acid and alkline situations while the inhibition activity falls down in extra acid and extra alkline situations.The activity of the fermentation would be reinforced when the initiative pH is 7.(3)By means of mycelium growth rate we measured the antibiogram of Xi-55 atrain,its fermentation products were against Alternaria citri,Ceratocystis fimbriata, Alternaria solani,Aloe black spot,Helminthosporium turcicum,Sclerotinia sclerotiorum,Fusarium graminearum,Botrytis cinerea,Fusarium solani,Pyricularia grisea,Cladosporium fulvum,Alternaria brassicae,Ustilaginoidea virens Uv-2,Uv-14,Uv-24,Uv-37 and so on.The results showed that the fermentation products of Xi-55 can resist many plant pathogenic fungus. (4)Control efficacy of Bacillus subtilis strain Xi-55 against rice false smut in the greenhouse and field was tested.Greenhouse experiments showed that fermentation broth of Bacillus subtilis strain Xi-55 had a certain effect against rice false smut.However,there is still a certain gap compared with Adriamycin Jinggangmycin.Field experiments showed that fermentation broth of Bacillus subtilis strain Xi-55 had a certain effect against rice false smut as individual application,but it is not ideal,fermentation broth of Bacillus subtilis strain Xi-55 related to anti-pharmacertical compound greatly enhanced efficiency.Especially fermentation broth of Bacillus subtilis strain Xi-55 with Adriamycin Jinggangmycin compound made control effect best in the test.