Identifieation Of Marine HW-14Antagonist To Magnaporthe Grisea And Its Antimicrobial Substances

Rice blast (Magnaporthe grisea) is one of the most serious diseases in rice production allover the world. Continuous application of chemical pesticides could cause significant problemon food safety and environment security. It is necessary to develop microbial pesticidesagainst rice blast. With the finding of more and more marine microorganisms, an increasinginterest has been focused on these organisms for novel compounds or molecular structures. Soit has become a hot research area to screen active substances from marine microorganisms.This test is intended to investigate marine microorganisms antagonistic to the pathogen of riceblast, screen antimicrobial substances from fermentation broth, and develop an effectivemicrobial pesticide for biological control of rice blast.Totally184strains of microorganisms were isolated from marine samples by platedilution method. From which nine bacterial strains were found to be antagonistic to M. griseastrain815by using cylinder plate method. After repeating tests of dual culture strain HW-14was demonstrated to be most evidently inhibitory to the pathogen and also antagonistic to theother physiological races with more than18mm diameters of inhibition zone. The in vitro testshowed that strain HW-14was also inhibitory to such plant pathogenic fungi as Fusariumgraminearum, F. oxysporum f.sp. vasinfectum, Exerohilum turcicum and Phytophthoranicotianae.Based on physiological and biochemical characteristics and16S rDNA sequence analysisstrain HW-14was identified as Bacillus subtilis.By single-factor experiment, the optimum liquid fermentation conditions for strainHW-14were outlined as follows, initial pH=7.0, inoculation amount6%,80mL of liquidmedium in250mL flask, rotation speeds180r/min, at30℃for72h.The observation under light microscope and scanning electron microscope showed thatthe middle and top mycelia cells of M. grisea became irregularly swelling or distorted aftertreated with fermentation broth. The further investigation showed that the sedimentsgenerated by30%ammonium sulfate saturation solution and acid precipitation and volatilecompounds were all inhibitory to M. grisea, of which the sediments produced by acidprecipitation and volatile compounds exhibited the most evident inhibition to M. grisea.