Isolation And Identification Of Actinomyces Antagonistic To Soft Rot Of Amorphophallus Konjac And Initial Study On Its Application

In this paper, several actinomycetes antagonistic to soft rot ofAmorphophallus konjac were screened. A novel actinomycete strain, SJK18, wasidentified, and its culture conditons were optimized. The major antibacterialmetabolites of the SJK18was separated and its chemical structure was identified.To investigate the disease-resistant effect of SJK18against soft rot of A. konjac inthe pot and filed, the complex microorganisms has been made by mixturingSJK18with antagonistic actinomycetes, endophytic bacteria of Amorphophalluskonjac, phosphate-solubilizing fungi and Azotobacter, and then inoculated to theroot of the A. konjac plants which were also deal with soft rot pathogen. Theresults were as follow:(1)11actinomycetes strains antagonistic to soft rot of A. konjac werescreened. One of these strains-SJK18, which could control soft rot effectively andantagonistic to bacterial blight pathogens of rice, was obtained by re-screening.The antibacterial rates of SJK18antagonistic to four rice blastpathogens(65A,1073-2,1366and IK81-3), a potato dry rot pathogen, a tomatoearly blight pathogen, a apple anthracnose pathogen and a pear decay pathogenwere62.2%,73.3%,62.5%,68.3%,49.1%,60.0%,66.4%and46.6%,respectively.(2) The strain SJK18was identified as one subspecies of the streptomycesfradiae by the traditional and molecular classification method, combining to thestructure analysis of its metabolic activity of material. The registration numbers ofthe strain’s16S rRNA gene sequence and16S-23S rRNA gene sequence inGenBank are JN256680and JN381162, respectively.(3) The culture conditions of sporulation of strain SJK18were studied, andthe results showed that the temperature at35℃and the pH at6.0made it easierto sporulate. The sporulation medium was a composite of0.2%peptone,0.3%NaCl and0.3%beef extract.(4) Using the antibacterial activity of the fermentation supernatant of the asthe content index, SJK18was cultured in Gause synthesis medium to optimizethe fermentation conditions, according to Single factor test, the optimumfermentation conditions were: fermentation time7days, temperature30℃, rotinal speed160rpm, inoculation0.4%, initial pH6.0, carbon source and nitrogensource were corn flour and KNO3respectively. According to the orthogonalexperiment, the optimized fermentation medium containing2.5%carbon source,0.1%KNO3,0.2%NaCl,0.04%KH2PO4,0.04%MgSO47H2O, and1mL/L of traceelements.(5) The main antibacterial composition of the SJK18grown in Gausesynthesis medium has been separated by precipitation, concentration andcrystallization, and then identified as phenol by using IR, NMR and TLC.(6) In potting test, the disease occurrence rates of A.konjac of thenon-treatment control were13.3%, but the disease occurrence of the A.konjactreated with the complex microorganisms containing SJK18; SJK4; SJK5; SJK10;antagonistic actinomycetes; endophytic bacteria of A.konjac, phosphatesolubilizing fungi and azotobacter was very lower. Compared with thenon-treatment control, the complex microorganisms could improve the growthleaves and increase both wet weight and dry weight of corms of A.konjac. Thecontents of glucomannan (KGM) of A.konjac treated with the complexmicroorganisms were increased by9.50%,4.25%,21.22%,16.97%,42.20%and50.00%, respectively.(7) The complex microbial community (CMC), made of antagonisticactinomycetes （SJK18、SJK4、SJK5and SJK10）, endophytic bacteria of konjac（N8）,azotobacter（G3、G4and G8）and phosphate-solubilizing fungi（P1、P7and P8）, was applied to biocontrol to soft rot of A.konjac in field test. Theresults showed that the disease occurrence rates of soft rot decreased by54.17%when the CMC was applied to the root of A.konjac. The relative control efficiencyof the CMC was61.91%. Compared with the non-treatment control, the KGMcontent of the A.konjac treated by CMC increased by30.15%.