| The sesame damping-off,caused by Rhizoctonia solani,is a serious soil borne disease which distributes widely in China sesame growing area.It does serious harm to sesame production.R. solani currently is being controlled in the sesame seedling by the use of chemical pesticides in the seed pellet.However,there is increasing pressure to find alternative to chemical pesticides for disease control due to their perceived detrimental effect on the environment.At present,as there is no resistant variety,it is necessary for us to find an alternative method to take the place of chemical pesticides.The using of plant endophytic bacteria and its metabolite for biocontrol against the sesame damping-off could overcome the shortage of chemical pesticides,and what's more important, the endophytic bacteria can exit in plant cell and can control disease stably.So it has much theoretical significance and applicable value.The main objectives of this study were:to isolate endophytic bacteria from sesame root,to screen biocontrol bacteria that can control sesame damping-off,and to analyze the characteristics and the colonization of these biocontrol bacteria.Total 399 endophytic bacteria were isolated from inner roots of 72 healthy sesame varieties grown in the field by the methods of surface disinfection and spread plate.The results showed that both the endophytic bacteria species and the population density are differences between different sesame varieties,and this is also the case with the same variety from different sites.Antagonistic activities of endophytic bacteria against R.solani were assayed on dual culture plates,and three mediums,PDA,KBM,and MYG,were utilized to screening the Antagonists.The results showed that 210 endophytic bacteria isolates had antagonistic activities toward the R.solani to some extent on three different mediums.In the experiment,inculaion of pathogen with 1:1 000(W/W) mixtures of R.solani and soil has been examined as the best ratio.On this basis,the system for screening of biocontrol strains in vivo was established with this system,210 bacteria were tested for their ability to control sesame damping-off in pot.The results indicated six isolates,including B16,b10,D31,e23,G10 and I10, could control the damping-off to some extent,and the best control efficiency was achieved by isolate G10,which reach to 52%and 42.5%in pot and field experiment respectively.All of the six isolates could also inhibit the growth of other pathogenic fungi including Fusarium oxysporium, Colletotrichum orbiculare,Gaeumannoyces graminis var.tritici and Sclerotinia sclerotiorum. Abilities to produce chitinase and chitosanase of six isolates above were assayed on culture plates with colloidal chitin and colloidal chitosan as the sole carbon source,which revealed that the strains of b10,G10 and 110 could produce chitosanase and chitinase respectively.Endophytic colonization of G10 within roots of sesame was tested on selective medium with colloidal chitosan as sole carbon source;the results indicated the isolate G10 could maintain a population of 10~6 cfu/g in the roots of sesame 20 days after seed pelleting inoculation or watering roots inoculation.Then experiment was carried out to test the characteristics of the strain G10.By physiological characteristics and the procedure of 16SrDNA identification the strain G 10 belongs to Bacillus subtilis. |
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