Screening, Identification And Characterization Of Rice Endophytic Actinomycetes Against The Pathogen Of Rice Blast

Rice blast is one of the most wide-spread and severe diseases in the world. Thediversity of pathogenicity and frequent mutation caused by the perplexing geneticfeatures of Magnaporthe grisea often result in loss of resistance of new breedingvariants and of benefits of chemical pesticides in several years. So the biologicalcontrol of rice blast gains attention gradually. Endophyte is a significant constituent inthe microbial ecosystem of plants, which can survive in the plants bodies, mea nwhile,does not exert obvious noxious effects on plants. Some researchers have alreadydiscovered that multifarious and abundant bioactive metabolites could be found inendophyte actinomycetes. These metabolic products have many valuable functionssuch as promoting growth of plants, resistance to stress, resistance to diseases andinsects invading and so on. Therefore, the development and utilization of endophyteactinomycetes is momentous for the biological control of rice blast. To develop newbiological control agents, we isolated and screened the endophyte actinomycetes thathave potential ability of inhibiting rice blast from the rice samples growing in Hunanprovince.1. Two rice variesties Xiangaizao7and Gumei4, which is susceptible andantagonized with broad-spectrum to rice blast respectively, were chosen as the researchmaterials. The endophytes were isolated from infected and uninfected Xiangaizao7andGumei4rice samples respectively when they were2,4,7,11,16,19-week-old. Theisolation results of samples collected in the year of2012showed that the amount ofendophyte actinomycetes isolated in vegetative stage overshadowed that inreproductive stage. The endophyte actinomycetes obtained from uninfected rice have aquantitative superiority compared with the infected rice.233strains of endophyteactinomycetes acquired from2-and4-week-old uninfected rice of can be account for55percent of all the isolated endophytes.2.171strains of endophyte actinomycetes isolated from4-week-old rice samplescollected in2012were used to employ the rice blast antagonism experiments.5strainsof actinomycetes, Sh-1, Sh-2, Sh-3, Sh-4and Sh-5, were all isolated from uninfectedrice. We found that Sh-2has the most prominent effect of countermining rice blastafter secondary screening via the antagonism effects to5distinct physiological racesof rice blast pathogen. The growth of the pathogen was effectively inhibited by Sh-2inPDA culture medium, at the28°C. The fermentation broth was collected after7days culture at28°C and150r/min shaking in ISP II liquid medium to do the antagonismexperiment. The inhibition zone in PDA culture medium can be observed clearly afteradding Sh-2fermentation broth. The Sh-2was ideinifed as Strepmyces hygroscopicusby16s rRNA and morphology ananysis. We named it as OsiSh-2.3. We further studied the bioactive substances extracted from OsiSh-2that mayinhibit the growth of pathogen. Chitinase and cellulase, which respond for thedegradation of cell wall of pathogen fungi, and the siderophore, which causes thecompetitive inhibition with pathogen fungi, were found in OsiSh-2. The highestconcentration of132mg/L of heteroauxin which promotes growth of plants can beproduced by OsiSh-2when cultured in liquid medium containing tryptophan. Theartificial infection test suggests that OsiSh-2could re-colonize in rice. Thesecharacteristics of OsiSh-2represent its great potential application in bicontrol of riceblast and in development of innovative medicine.