Identification And Screening Of Antagonistic Bacterium Against Rhizoctonia Solani And Its Control Effect In The Field

Rice sheath blight,also known as moire,was one of the important diseases which do harm to the rice.It occurred in every main rice production regions and caused 10-30%of economic losses each year,even 50%losses.Rhizoctonia solani,the pathogen of rice sheath blight which possessed parasitic and saprophytic life,has an extensive range of hosts.Sclerotium were the important sources of infection to infect rice and has difficulty in controlling because of the strong ability to stand up to the adverse environment and existed in soil.Validamycin,usually used to control rice sheath blight on production but has been utilized over 20 years,had be proved that existed drug-resistance risks in fields.So,there is no time to delay to explore some new methods to control rice sheath blight.Biological control with efficiency?low toxicity?security can reduce environment pollution and pesticide residue,is gradually becoming the focus of study.Recently,many researching institutions had screened the antagonisms to control Rhizoctonia solani.However,because of the limitation of environmental conditions,many antagonisms still unstable and easy to degradation in assays in the field.So it's necessary to screen the antagonistic strains again.This study was based on the previously and aims to screen the antagonisms which can resists Rhizoctonia solani from rice-duck multiple planting fields,then identify the strains to determining the antibiotic active ingredients and the control efficiency in fields.The main results are as follows.1)Screening antagonistic bacteria against Rhizoctonia solaniUtilized dilute separation to separated 300 bacteria from rice-duck multiple planting fields,the results revealed that 24 bacteria about 8%has antagonistic activation to Rhizoctonia solani.According to colonial morphology,they can be divided into four parts of round?irregularity?radial pattern and oval.On the basis of surface polish of colonies,they were smooth surface and rough surface.In accordance with the orderliness of colonial edge,they can be divided into orderliness strains and irregularity strains.Because of different colors,colonies be split into canary?incanus?lacte?pale?brown and lavender.While according to the transparency of colonies,they can be divided into lustre type and opacity type.Among 24 antagonistic bacteria,B137W showed the most efficient and stable inhibit impact on Rhizoctonia solani,the inhibition rate was 72.32%,while the inhibition effect of others were weak.Therefore,this study selected antagonistic bacteria B137W?Strain B137W?to control Rhizoctonia solani and prepared to the further study.2)Identification of strain B137W against Rhizoctonia solaniThe research showed that the strain B137W had the best antagonistic effect of Rhizoctonia solani with 20 mm inhibition zone.The second-best inhibition effect was to Colletotrichum capsici and Magnaporthe grisea with 10mm inhibition zone.It also had antagonistic effect of Ustilaginoidea virens,Colletotrichum fragariae,Botrytis cinerea,Alternaria alternata,Phytophthora parasitica and Penicillium italicum with with 8 mm inhibition zone.However,there was no inhibition to Phytophthora capsici Sclerotinia sclerotiorum and Verticillium dahilae.The strain B137W could grow in abundant medium,particularly in NA medium,because of its broaden nutrition zone.It's colony was round,white,rough,opacity,lackluster,no pigment regular edge,protuberance and flat.This was a gram negative bacteria with rod shape or short rod shape,had flagellum,no capsule,no spore and columned shape.It about1um and also had a smooth surface,rod shape or short rod shape,regular edge and no indentation.It can make oxidase positive,catalase positive,gelatin liquefaction,amylolysis,a movement,grow in the 28?,citrate positive,malonate positive and acetate positive.But it made lecithinase negative,fibrinolysis negative,methyl red test negative,indole test negative,H₂S negative,nitrate reduction test negative,V-P test negative,glucose negative,maltose negative,sucrose negative and xylose negative.According to these biological characteristics,we could first identify that the strain B137W is belong to alcaligenes genus.Molecular biological identification result showed that the sequence of 16s rDNA was1433bp.We compared this sequence to NCBI find that B137W had 100%homology with Alcaligenes faecalis.The phylogenetical tree also showed that B137W was very close to Alcaligenes faecalisin the evolutionary status.Combining the molecular biological identification result with morphology and physiology and biochemistry test result,we identified that the B137W was Alcaligenes faecalis.3)Antifungal active extract analysis of the strain B137WGC-MS was applied to analysis antibacterial active extract of the strain B137W each component's mass fraction was calculated according to the area method.Based on more than1%of each component,more than 80%of the calculations were calculated,and 43compounds were detected and 36 compounds were identified,accounting for 83.72%of the total component.The antimicrobial active extract of the strain were mainly aldehydes,acids,ketones,esters,alkane,alcohols,amines,peptides,piperazine and phenols.Antibacterial acids substance and alkanes proportion reached 24.24%,the ester material accounts for15.15%,ketone material accounts for 12.12%,piperazine and amine substance was 6.06%,other substances,such as:phenolics,alcohols,and the peptides material accounts for the same proportion of 3.03%.4)Control effect strain B137W active extract against rice sheath blightAntibacterial active extract of the strain B137W had a good control effect against rice sheath blight.The higher concentration of active extract,the better the anti-disease effect,the best control effect can be 82.15%,which was 1.16 times higher than the antiagent.It was indicated that the strain can have a good control effect against rice sheath blight,therefore,it was possible to consider to develop the strain as an alternative strain of biological pesticide.In addition,the active extract of strain B137W had no effect on the normal growth of rice.It suggested that the active extract were safe for the growth of rice and could be popularized and applied in production.