| Tobacco black shank caused by Phytophthora parasitica,tobacco bacterial wilt caused by Ralstonia solannacearum,are the important diseases with serious loss in the tobacco area of Chongqing.Biocontrol is an promising measure of methods in tobacco disease control.Actinomycetes is important source with potential biocontrol effect.In this study,some actinomyces strains with antagonistic Phytophthora parasitica & Ralstonia solannacearum were isolated from tobacco rhizosphere soil in main tobacco areas of China,the control efficacy at greenhouse experiment,taxonomic identification,and the biocontrol mechanism by analyzed.1.57 soil samples of tobacco fields were collected from Chonging,Guizhou, Yunnan,Henan,Shannxi and Shandong provinces,the main tobacco planting areas of China.A total number of 415 isolates of actinomycetes were isolated by dilution cultured on Gause's Synthetic Agar plate.2.The all of actinomycetes isolates by tested with the Phytophthora parasitica by pairing culture on plate method,and with the Ralstonia solannacearum by plate spraying method.And 178(42.9%of the all isolates) were found to be antagonistic effect against the pathogen.134(32.3%of the all isolates) against Phytophthora parasitica,which i.e.were 77 isolates(18.6%) agianst Ralstonia solannacearum and the 33 isolates(7.95%) can antagonistic the both pathogens.3.Farther screening were carried out by each strain with plate inhibition effect against Phytophthora parasitica over 10 mm inhibition radius and against Ralstonia solannacearum over 5 mm inhabition radius.The results showed that 11 strains had good antagonistic effects on Phytophthora parasitica,and the inhibition zone diameters ranged from 15 to 35 mm,in which the inhibition zone of strain HLL3-4 and BX2-5-4 were 33.3 mm and 32mm,respectively.7 strains which against Ralstonia solannacearum were found the inhibition zone diameters ranged from 35 to 55mm,the inhibition diameters of strain GAS1-9 and YYD3-32 were over than 50mm.4.The results showed that the zymolysis liquid of all the actinomycetes had good biocontrol effects against the two diseases at the greenhouse experiments.The biocontrol effect against Phytophthora parasitica ranged from 38.13%to 88.89%.In which have 8(61.5%of the all strains)strains with relative efficiency over 50%,2 strains with relative efficiency over 80%were BX 2-5-4 strain and BX 1-1 strain, which the control effect reach to 88.89%and 88.13%,respectively..The biocontrol effect of actinomycetes against Ralstonia solannacearum ranged from 37.89%to 90.06 %.In which have 6(85.7%of the all strains) with relative efficiency over 60%,the strains SXL1-7 had the best control effect of 90.06%,followed the strain GAS1-9 with the control effect of 85.72%.5.Based on the characteristics of morphology and physiology-biochemistry,plate screening and greenhouse experiment,13 antagonsists were primarily identified as actinomycetes.In which 6 strains belong to Streptromyces including Albosporus, Viridis,Flavus,Roseosporus Fradiae,and 3 strains belong to Streptroverticillium,other 3 stains belong to Saccharomonospora,Elytrosporangium and Actinosporangium respectively.Furthermore,5 strains had good biocontrol effect at greenhouse were analyzed with morphology,physiological and biochemical properties,16S rDNA phylogenetic tree,the results showed that the GAS1-9 was identified as Streptromyces rochei,BX1-1 was Streptromyces variabilis,BX2-5-4 was Streptromyces hygroscopicus,SYZ2-6 was Actinomycetales bacterium,SXL1-7 was Streptromyces plicatus.6.Analysis of the metabolic producetions of the five strains,the results indicated all of the strains have good biocontrol effects,and the strains SYZ2-6 and BX1-1 could produce active substance for biocontrol,such as chitinase,cellulases,proteases, siderophores and so on. |
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