| Maize sheath blight is a maize diseases of corn which is destructive soil-borne disease and causes significant yield loss. Rhizoctonia solani, Rhizoctonia zeae Voorhees, Rhizoctonia cerealis was three important pathogen of a Bacillus subtilis from the soil of Maize sheath blight and the train has strang antagonistic action against disease.Isolated pathogen from maize sheath of disease and 23 strains antagonized this disease form maize rhizosphere soil of disease. Identification pathogen is Rhizoctonia solani which is belonged to deuteromycetes Rhizoctonia and the pathogen has pathogenicity.4 highly chitinase strains was screened from confront culture against pathogen, stess resistanse of adverse environment which incolding incubation tempreture, incubation time, medium component, chitinase determination of strains with chitin-flat-band method and direct chitinase determination.4 strains was identificated, which one strain of them is Bacillus subtilis and three stains of them are Bacillus subtilis, and Bacillus subtilis 515 has the strongest stress resistance, the higheast chitinase and bigeast decomposing ring against disease.Standerd chitinase dilute lever of 0.4U/ml,0.6 U/ml,0.8 U/ml and add into conical flask which including three sclertiums respectively, repeated 3 times, weigh the mycelium without water before culture 24h,48h,72h and 96h.The results showed that the standed chitinase of 1.6 U/ml lever has the strongest antagonistic effect against mycelium of Rhizoctonia solani, and the mycelium growth is related to culture time, the more longer of culture time, the more weighty the mycelium is.Ammonia sulfate of different strengths which lever is 10%,30%,45%,60%,75%, 90% extract crude protein. The 45% strengths lever of Ammonia sulfate has the strongest antagonistic effect against disease and the highest chitinase, but component of crude protein is needed further analysis.A higher chitinase production mutant with stable heritage, was obtained from initial Bacillus subtilis 515 strain, which was separated from soil and by means of UV which radiation time is 150s,200s,250s,300s respectively, LiCl which strengths lever is 0.3%, 0.6%,0.9%,1.2%,1.5% and DES which cultivate time is 20,40,60,80min mutagenization. The result showed that the best UV mutagenic time is 200s, the LiCL strengths is 0.9% and DES mutagenic time is 45min.The chitinase activity of Bacillus subtilis 515 increased to 2.09 times compared with that the initial strain.The optimum medium and fermentation condition for Bacillus subtilis 515 have been established through orthogonal test design. Under the established optimal culture conditions which incoulding colloidal chitin 1.0%, beef extract 0.4%, peptone 0.4%, KH2PO40.04%, MgSO4.7H2O0.06% and in the established optimal medium which incoulding temperature 35℃, fermentation time 18h, ph 6.5, inoculum size 7%, Throughput 50ml/250ml. The chitinase activity of Bacillus subtilis 515 increased to.53U/ml compared with that the initial strain under the culture condition before optimization.The soil bacteria Bacillus subtilis 515-126, which was isolated from maize soil rhizosphere was an efficacy biological control of Rhizoctonia solani.A strain resistant rifampin derivative of Bacillus subtilis 515-126 was used to study the colonization ability and fluctuation of population in maize rhizosphere soil, maize root surface and maize sheath, and its biological control on Rhizoctonia solani.The result indicated that strain 515-126 could colonize in both rhizosphere soil and root surface, and could not colonize in maize sheath. The strain in the sterile soil have the higher colonization than in the natural condition.The disease indes of strain is 26.67%, which is lower than the treat of CK and higher than the treat of validamycin. The control efficacy of strain is 49.17%, which is lower than the treat of validamycin.And the train could reduce the disease incidence of Rhizoctonia solani.
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