| Take-all of wheat caused by Gaeumannomyces graminis var.tritici (Ggt) is one of the important soil-borne plant disease.It is widespread all over the world where wheat is grown. None of resistant varieties are available and the methods of control to the take-all mainly relied on chemical pesticide and crop rotation at present, but the efficiency of crop rotation is not good, the negative effect to environment and the emergence of pesticide resistance strains of chemical pesticide are also more and more serious. So a new control measure is necessary. The benefic microorganism to control the take-all of wheat become to be a hot research. The main objective of this research is to isolate endophytic bacteria from wheat and screen biocontrol bacteria that can control take-all of wheat, and research its biocontrol agents and to determine the machinism. The final aim is to formulate a biological solution which can use under the field condition.At first, 410 endophytic bacteria strains were isolated from the roots of healthy wheat. Through the primary assay, ten strains which had the ability to control the take-all of wheat in vitro were screened, they were named as 3-36, 5-36, 7-12, 5-61, 2-32, 5-3, 2-2, 3-19, 19-22 and 3-17. The average efficacy of biological control of them were 89.5%, 73%, 74%, 80.5%, 63%, 42.5%, 55.7%, 46%, 60.2% and 71.2% respectively. Among them, 3-36, 5-36 and 5-3 could reduce the incidence of take-all, especially the strain 3-36 had the best efficacy, it could significantly reduce the disease index and the incidence of take-all. By physiological characteristics and the procedure of 16s rRNA identifieation, the strain 3-36 belongs to Serratia Proteamaculans.Afterwards, the machinisms of them were studied, The mainly results of the research are as follows:Inhibition to take-all 9812 was done on three kinds of medium, they were King's medium B ager, liquid broth and potato D-Glucose ager. The reslutes suggested that strain named 7-12 had the best powerfull ability to inhibite the take-all, 3-36, 5-36, 5-3 and 3-17 hadn't the ability. But the inhibition states on the three kinds of medium were not the same. Though the strain 3-36 had the best biological efficacy, it hadn't the inhibition zone, this suggested that the controlling of strain 3-36 to take-all is not by generating antibiotic.The result of induce system resistance (ISR) assay suggested that ISR was the machinism of strains 19-22 and 3-17. ISR played a key role on 3-36, 7-12, 3-19, 5-3, 2-2, 5-36 and 2-32 controlling take-all, but ISR was not the only machinism.Meanwhile, the result also showed spliting root of wheat was a efficient method to prove the role of ISR in biological control. Strain 3-36 also generate chitinase and siderophroes, the role of the two substances in biological control machinism would be done in the following assays.Biparental mating of the endophytic bacteria 3-36 was performed with E. coli strains containing plasmid pRL1063a, which harbors a Tn5luxAB transposon and kanamycin marker gene. 500 transconjugants were obtained after transposon mutagenesis. Then A-98 was selected randomly to determine the colonization capacities of 3-36 within several crops including two kinds of wheat, cucumber,corn, mung bean,cabbage and millet. These results suggested that there should be selectivity between endophytic bacteria and its original host. Meantime,the result proved that 3-36 had wide spectrum ability to colonize in different crops. |
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