Screening Of Biocontrol Bacteria And Performce Against Tomato Damping-off

Tomato damping-off,caused by Rhizoctonia solani,is an important soil-borne disease at tomato seedling stage.Biological control is considered to be an effective way to control soil-borne disease.In order to screen the biocontrol bacteria for effective control of tomato damping-off,a bacterial strain,which inhibited the growth of R.solani,was isolated from the rhizosphere soil of tomato collected from different cities and counties in Guangxi,and its main biological characteristics were determined.The bacteriostatic effect of the strain against R.solani and its growth promoting effect on tomato were preliminarily analyzed.Furthemore,the control effect of the mixture of the strain and bactericide on tomato damping-off was also tested.The main results are as follows:1.A total of 2160 bacterium strains were isolated from 84 soil samples collected from Nanning,Laibin and Baise city of Guangxi.Of which,109 strains presented antagonistic activity against R.solani by dual culture method,and 37 strains with the bacteriostatic rate more than50%were selected to test their control efficiency against tomato damping-off.The result showed that strain B11-64 at the concentration of 5×10~8CFU/m L could control the disease effectively,with the control efficiency of 86.11%in pot,and 41.67%in the field.Strain B11-64presented highly inhibitory against Sclerotium rolfsii,Fusarium oxysporum,Deightoniella torulosa,Phoma sorghina,Diaporthe citri,Pythium aphanidermatum and Colletotrichum siamense,which inhibition ratio were 62.04%?57.73%?80.81%?69.48%?59.84%?80.40%and 58.84%,resoectively.Based on the morphological,physiological,biochemical characteristcs and 16S r RNA sequence analysis,strain B11-64 was identified as Pseudomonas chlororaphis.2.In the condition of presenting sucrose as carbon source,yeast extract as nitrogen source,temperature 30?and p H=8,the biomass and antagonistic activity of strain B11-64 were at a high level.Strain B11-64could form biofilm and survive in the rhizosphere soil of tomato stably.3.Strain B11-64 presented a certain promoting effect on the rooting numbers and stem thick and single fruit weight of tomato,but it could not promote the seed germination and height of tomato plant.B11-64strain cultured in King's B medium for 12 days,the IAA content in the medium was 29.44?g/m L,After 14 days'growth,the average rooting numbers of tomato seedlings treated the fermentation liquid of strain B11-64 diluted 10 times and treated with 2.944?g/m L IAA were 64 and69,respectively,which were significantly higher than those of the blank control group(29.5).The germination rate of tomato seeds treated with fresh bacterial solution of strain B11-64 for 7 days,the treatment group was 72.22%,and the CK group was 74.44%,both at the same level.Cultivated in the field for 102 days,the height of tomato treated with strain B11-64 was 99.46 cm,which was at the same level as that of CK group(100.22 cm);the stem diameter of strain B11-64 treatment was1.52 cm,which was significantly larger than that of CK group(1.36 cm);the single fruit weight of tomato treated with strain B11-64 was 99.64 g,which was significantly larger than that of CK group(85.51 g).4.Strain B11-64 could destroy the mycelium structure of R.solani,and could be metabolized to produce HCN.The genes of phz CD related to the synthesis of phenazine-1-carboxylic acid in strain B11-64 were found by PCR amplification test,the results of thin layer chromatography confirmed that the strain could produce phenazine-1-carboxylic acid.The plate bacteriostatic test showed that phenazine-1-carboxylic acid at the concentration of 100?g/m L could not inhibit the growth of R.solani,while the crude extract of phenazine-1-carboxylic acid presented a certain inhibitory effect on pathogen,indicating that the crude extract had other substances that inhibited the growth of R.solani.5.Strain B11-64 could grow on NA medium containing 25%pyraclostrobin SC at the concentration of 50?g/m L.Strain B11-64mixture with 25%pyraclostrobin SC had synergism with co-toxicity coefficient of 151.38 on R.solani.The control efficiency of the mixture at the concentration of 50 mg/kg on tomato damping-off was 80.36%in pot,and was 80.64%in the field.The control efficiency of strain B11-64at the concentration of 5×10~8 CFU/m L and 25%pyraclostrobin SC at the concentration of 50 mg/kg were 66.96%and 79.46%in pot,and were51.28%and 73.14%in the field,respectively.The result indicated that the mixture was more effective in reducing tomato damping-off than that of strain B11-64 and 25%pyraclostrobin SC alone,and showed that the mixture of strain B11-64 and the bactericide could improve the control effect of B11-64 on tomato damping-off.In a conclusion,strain B11-64 is a bio-control strain with antagonistic ability to R.solani and certain growth promoting ability,which is suitable for controlling tomato damping-off.