Screening Of The Active Strains Of Marine Microbial Resistance To Rice Blast Fungus (pyricularia Grisea)

Rice blast is one of the most severe disease of the rice. This thesis reported screening on marine microorganisms antagonized Pyricularia grisea, using a screening model based on observing inhibiton of the co'udiospore of P. grisea.Seventy-one marine samples were collected from South Sea, Xisha, North Bay and near shore coast of Hainan Island. During the isolation procedure, some effective media, such as Cause's Synthetic Medium, Emerson's Medium, Soil Extract Agar, Ml Medium, YE Agar, V8 Vegetable Juice Agar, Starch Agar Medium, Martin Medium and so on, and pretreatments, as heat, SDS, phenol, chitin enrichment, chlormycetin enrichment were conducted and some inhibition agents were added into the media. Six hundred and forty-six strains were isolated, including 297 of bacteria, 111 of filamentous fungi and 238 of actinomycetes.Among 1593 isolates to be screened, including 947 isolates isolated by collaborators in this project, 468 active isolates showed primarily bioactivity against rice blast in the laboratory, based on two screening methods and the percentage of active isolates was 29.4%.Effects of seven factors on the percentage of active isolates obtained were tested using SAS 8.2 statistic software. Effects of sample types, pretreatments, microorganism types and antagonizing time of agar diffusing method on percentage of active isolates reached the greatly significant level. Sample locations showed significant effects. Media used for isolations and different screening methods showed low effects on percentage of active isolates.Eighty-four isolates still showed strong bioactivity against rice blast after the third screening. After the fourth screening, 14 isolates still showed high activity, including 7 very high isolates. Among them, strain 031057 showed stable bioactivity.Both the two screening methods were suitable to be used as the primary screening methods. Between them, Agar Diffusing Methods showed higher false negative rate in detection, and 96-well Plate Method showed higher false positive rate.Strain 031057 was isolated from sea sand, collected from the South Sea. It was a bacterium with endospore, not movable, belonged to G+.Relative inhibition concentration of the bioactivity produced by 031057 was 100 mg/mL corresponding to hygromycin B. Its maximum cell density was 3.68+07 CPU /mL after fermentation for 24 h and reached its maximum bioactivity after 5 d.Bioactivity of 031057 was not affected by aeration. It could stand salinity up to 5.42%, but its bioactivity producing was not dependant salt. It produced maximum bioactivity in Soybean Liquid Mdium without salt.Among 5 media, strain 031057 produced maximum bioactivity in Soybean Liquid Mdium.Bioactive substance produced by strain 031057 was stable at heat, preservation under room temperature, dry procession, but not stable at acid and alkali conditions. Strain 031057 produced water-soluble extracellular bioactive substance, which was deposited by ethanol and acetone and denaturalized completely by ethanol and half denaturalized by acetone. Organic agent inactivated it. The active substance was primarily speculated to be a hybri-protein.Strain 031057 showed a narrow inhibition range and its control on the rice blast in the lab was at 1/500 concentration. It did not cause damage to the rice.