Studies On Isolation And Application Of Agricultural Antibiotics With Antifungal Activities

It is reported by FAO that 37% of the output value in agriculture and forestry is lost because of insects, diseases and weeds every year, the lost money, which equals to half of Chinese agriculture output value or over 4 times of British's, reaches 126 billion dollars. Chemical pesticide is the main means in past decades to control pests, diseases and weeds, but the mass use of great poisonous and rudimental chemical pesticides is threatening our environment and human being's health badly. Study and application of biological pesticide have become the direction gradually, furthermore, with more and more attention public gives to green food and unpolluted food, the marketable foreground of biological pesticide is becoming better and better. Agricultural antibiotic is the principle part of biological pesticide, many countries in the world attach great importance to agricultural antibiotics increasingly for its virtues such as high effect low pollution, function selectively, decomposed easily, safety from cancer, abnormality and mutation and no social effects of pollution. Some agricultural antibiotics have been applied successfully and widely in plant disease and pest control, examples include validamycin, abamectin, zhongshengmycin and ningnanmycin.Studies such as screening, purification and controlling in paddy field of agricultural antibiotics were conducted for controlling plant fungal diseases. The results as follows: '1) 253 actinomycetic isolates and 886 bacterial isolates were isolated from 11 soil samples collected in Yaan and Wenjiang, Sichuan. 51 actinomycetic strains (20.16%) and 173 bacterial strains (19.53%) with antagonistic activities were screened out by dual culture test. Strong antagonistic strains D-2 and LM-3 were determined according to the extent of inhibition, physiological and biochemical characteristics and stability of the active components. Based on the morphological growth, physiological and biochemical characteristics and chemical components of cell wall, strain D-2 and LM-3 were determined to be Streptomyces cinereohygroscopicus and Paenibacillus polymyxa, respectively.2) It was showed that the inhibition rates of D-2 to M. grisea, Sclerotinia sclerotiorum, Fusarium graminearum and F. oxysporum were 92.2%, 78.9%, 53.3% and 52.2%, respectively by dual culture test on PDA plate. Crude antibiotics were obtained by ethyl acetate extraction and condensation from the fermented broth of D-2 strain, the antibiotics were unstable in acid condition and its activity kept steady in neutral or slight alkaline condition at 80℃ for 1 h, in visible light (4 000 lx) for 12 h and UV(2 400 lx) for 4 h. The main active components were purified by silica gel column chromatograph andsilica gel TLC. Nine biological pesticides were formulated with different solvents and emulsifiers to control rice blast in paddy field, it was showed that the best control effect was 65.69% with methanol as solvent and Tween 80 as emulsifier.3) Promoting ability of LM-3 strain was studied under the three treatments with seed soaking, shoot soaking and seedling irrigation; At the same time, the induction of three protecting enzymes including superoxide dismutase, peroxidase and catalase was studied under the treatment with LM-3 strain. The results showed that the best treatment in promotion experiment was seedling irrigation (2 x 106 cfu/ml) in which the five indexes such as shoot height had significant differences from CK and other treatments and that the three protecting enzymes were induced clearly. Antifungal Polypeptide produced by this strain was obtained by precipitation, It was showed on PDA plates that the development of many pathogens such as Colletotrichum gloeosporioides was inhibited by the antifungal polypeptide effectively. The polypeptide was found to be tolerant to Pronase E and trypsin and partially sensitive to proteinase K; After treated with high temperature (120"C) for 20 minutes, the antifungal polypeptide still reserved 84.71% of its antagonistic activity; It was steady at pH 8.5 but lost all its activity at pH 2.5, 80°C for an hour; It was tolerant under the treatment with UV (24001x, 8h). Analyzed by SDS-PAGE electrophoresis, the molecular weight of the polypeptide was between 6 kDa and 14.2 kDa.