Screening Of Bio-control Bacteria Against Phytophthora Parasitiva Var.nicotianae

10strains were obtained from this experiment. The basal portion of stem wereinoclucated by without wounded on differential hosts L8,NC1071, xiaohunagjin1025and florida301.The result of this study indicated that of the10strains,6strains wereindentified as race1,4strains were indentified as race0.The KRK26, Honghuadajinyuan,NC82and K326were used to indentify Differential Hosts,The result shows thatHonghuadajinyuan can replace the xiaohuangjin1025as susceptible cultivars todeterminate the physiological races. It also shows that the pathogenicity of those strainswas different to KRK26, NC82and K326. The3varieties can be used for determinatingthe pathogenicity differentiation.Gh·2was used to target cells in order to screening to pathogenicity of Phytophthoraparasitiva var.nicotianae, The antagonistic activities to Phytophthora parasiticavar.nicotianae were surveyed. The result of biocontrol research showed that,12strainswere screened out from which obviously antagonized against the growth of P. parasiticavar．nicotianae. The width of inhibitory zone all above6mm.. The result of16S rDNAPCR-RFLP analysis showed that the relationship of12strains antagonistic bacteria isvery close, Based on the partial sequences of16S rDNA analysis the strains were rankedinto Bacillus subtilis or Bacillus amyloliquefaciens.Growth promotion has been done by using12strains.The result shows that the12strains had growth-promoteing effect ontobacco seedlings,Especially YX-117andYX-69strains could significantly improve the leaf area,fresh weight of the overgroundpart and underground part.The results show that12strains on two different varieties of tobacco seedlings havea visible preventive effect on Phytophthora parasitica var. nicotianae, The control effectof12strains is60.00-84.14%in KRK26, The control effect of12strains is13.21-76.73%in Hongda,The best one is117strains, The control effect of117strains is84.14%in KRK26,and its control effect is76.73%in Hongda; The second is69strains,The control effect of69strains is77.25%in KRK26, and its control effect is74.21%inHongda.Colonization ability of YX-117and YX-69were determined by the method ofRif-resistant marker.The result that the colonization of2strains is the same in differentvarieties tobacco at the same time, Bacterial suspension concentration is higher, thegreater the amount of colonization. The population in soil were106cfu/g.In the processof colonization, the number of2strains kept reducing with the time passing. A largenumber of2strains can still be detected after fifty-six days.All of this, We know that theYX-117and YX-69have the great colonization ability in tobacco plant rhizosphere soil.