| Plant fungicidal disease is one of the most serious plant diseases,it is also one of the most primary reasons that cause agricultural loss. Fungi lives everywhere.Now, the number of the known species has reached 40 thousands,and the pathogens can be found on almost every kind of crop.One of the wheat diseases ,caused by Fusarium graminearum,is also called red head wheat.It is a destructive disease that can seriously influence the yield of wheat in the wheat growth area.The yield loss may reach 50% in some area. The prevention against the disease was always through agricultural and chemical measures since long before, but the effect of prevention was not good. Application of chemical pesticides brought entironment pollution. Biological control by natural antagonistic organisms is a potential measure against plant diseases. So in our test an antagonistic bacterium was primarily studied.Traditional phenotype classification,chemotaxonology and other ordinary bacteria taxonology were used to study the antagonistic bacterium preserved by the agricultural antibiotic laboratory of Chengdu Institute of Biology, Chinese Academy of Sciences.Its morphological,cultural physiological,biochemical characteristics and chemotaxonomy were studied.The antagonistic bacterium is bacilliform,and its cell diameter is less than 1 micron;it is Gram positive;it.can form spore.So it is a species of Bacillus.But the spore formed by this antagonistic bacterium can not make the sporangium swollen,and the parasporal crystal can not be formed. The antagonistic bacterium can be dyed equably by Methylene Blue.It can grow in pH5.7 culture medium and 7% NaCl. It is an aerobe,it can not grow without oxygen. Further more, the antagonistic bacterium can hydrolyze starch and deoxidize nitrate.So it was primarily identified as Bacillus subtilis.In the antifungal activity test,the method of sitzkrieg culture, asynchronism culture and hyphal extension inhibition assay of plate were adopted to study the inhibitive effect of the antagonist on Fusarium graminearum, and at the same time,the test conditions were explored.Adopting the assay method founded in the experiment to test the antifungal activity, the result showed that the antagonist produced by the Bacillus subtilis had obvious inhibitive effect on Fusarium graminearum.The medium recipe and fermentation conditions of the antagonistic bacterium were optimized through orthogonal experiment and single factor experiments.On the basis of the optimized medium, the effects of a number of factors on the production of Bacillus subtilis were studied,including original pH, incubative temperature and time, inoculation quantity and volume of culture media.The result showed that optimum medium was starch 0.75%, corn powder 1.0%, NaC1 0.90%, soya bean powder 2.5%, peptone 0.1%.The favorable fermentation condition was determined: temperature 28℃, original pH7.0—7.5, pack amount 8%～12% volume medium in triangle bottle, inoculation quantity 10% and shaker rotation speed 200r/min.Adopting ammonium sulphate and ethanol precipitation to explore the separation conditions,and some properties of the crude antifungal substance were studied subsequently, the result showed that the antifungal substance could be separated primarily by ammonium sulphate precipitation.It entirely deposited when the saturation of ammonium sulphate was at the range of 30%-70%.So it could be concluded that this antifungal substance was probably a protein. It was unsuitable to separate the antifungal substance by ethanol precipitation probably because there were too many ions in the supernatant fluid of Bacillus subtilis.The stability experiment result indicated that the antagonistic substande was stable against heat ,acid and alkali and enzyme.
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