Study On The Inhibition Of Antagonistic Bacillus On The Pathogens Of Soil Borne Diseases And Their Biological Characteristics

Soil borne plant diseases are difficult to be eradicated because of their concealment,hysteresis and epidemic characteristics,and their harm is increasingly serious,causing great losses to agricultural production.Although the effect of chemical control is good,it will cause a series of problems,such as environmental pollution,pesticide residues,pathogen resistance and so on.In the previous study,we obtained 6 strains of bacillus Spp.which had obvious inhibitory effect on bacterial wilt and Sclerotinia sclerotiorum of mulberry.strains(NN01,NN02,NN04,NN05,NN88 and NN95)were identified and their taxonomic status was clarified.The inhibition of spp.to seven soil borne pathogens was determined by plate confrontation and in vitro leaf inoculation.The antagonistic mechanism was studied by measuring extracellular enzyme activity,observing mycelial morphology and amplifying antibiotic producing genes The biological characteristics of these antagonistic strains were determined,and the basic growth rules of these antagonistic strains were preliminarily understood.The main results are as follows:1.According to the culture characteristics and morphological observation results,combined with 16 S r RNA and gyr B gene sequence analysis,six strains of antagonistic bacteria were identified as Bacillus velezensis.2.The results showed that NN01,NN02,NN04,NN05 and NN88 were resistant to sclerotium rolfsii,Sclerotinia sclerotiorum,Botrytis cinerea,Fusarium oxysporum f.sp.cubense and Rhizoctonia solani The results showed that solani had obvious inhibitory effect on the mycelial growth of Sclerotium mori,with the inhibition rate of 46.67 % ～ 76.11 %;NN95 had a poor inhibitory effect on the mycelial growth of all tested pathogens,and the inhibition rate was lower than 19.26 %;all strains had no obvious inhibitory effect on Phytophtora parasitica var.nicotianae Tucker and Pythium ultium.The results of leaf in vitro test showed that all the six strains could develop the Sclerotinia sclerotiorum and Sclerotinia sclerotiorum of lettuce.The inhibition rates of the six strains were53.40 % ～ 71.32 %,which were higher than those of the control(pyrimethanil)(52.50 %).Among them,NN01 had the best inhibition effect(85.71 %),and the inhibition rate of Sclerotinia sclerotiorum of lettuce ranged from 43.57 % to65.68 %.3.The results of transparent plate method showed that all the six antagonistic bacteria could produce cellulase and protease;after the plate confrontation culture,the antagonistic bacteria could significantly change the morphology of mycelia,such as protoplast concentration,hyphal rupture,protoplast leakage and mycelial color deepening;PCR detection results showed that all strains contained yndj,esculetin and antimycomycin Genes related to antibiotic production,such as enzyme and lysozyme,were also found in NN01,NN02,NN04,NN05 and NN88.4.The results showed that the optimum p H of NN01 and NN04 was7.0,that of NN02 and NN05 was 6.0,and that of NN88 was 8.0.The optimum growth salt concentration of NN01,NN02,NN05,NN88 and NN95 was 1%,and that of NN04 was 5%.The results of this study provided the strain resources and theoretical basis for biological control of main soil borne diseases,such as mulberry white silk disease,and laid the foundation for further study on the antibacterial mechanism of antagonistic bacteria.