| At present, the prevention and control of plant diseases on agricultural production mainly depends on chemical pesticides. With a wide range use of chemical pesticides, the eco-environment becomes deterioration. Therefore, to develop environmental-friendly source of biological pesticide became a focus of research areas.Lysobacter enzymogenes is a new kind of bio-control bacteria. It can produce severy secondary metabolites, among them, HSAF is a heat-stable, broad-spectrum antifungal factor which can be developed as a good source of biological pesticide, to achieve this purpose, this study adopted three steps to optimize the medium component:1. By adding different nitrogen sources and carbon sources to confirm that soybean powder as the best nitrogen source and glucose as the best carbon source, and then by the comprehensive experiment of three concentrations respectively (soybean powder:0.50%,0.70%,0.90%, glucose: 0.30%,0.50%,0.70%) to get the optimal proportion:0.70% soybean powder + 0.50% glucose.2. Used the best ratio of nitrogen source and carbon source, compared the effect of different inorganic salt of HSAF yield.3. Designed an orthogonal test to get the best media component. The result shown that soybean powder 0.50%、glucose 0.70%、 calcium chloride 0.08% is the best combination. After optimized, the production of HSAF was 13.9-fold while the cost was 32% that of 10%TSB. The optimization scheme not only greatly increased the output of HSAF, it also observably reduced the cost of fermentation. In addition, this study made an optimization of the fermentation conditions of L. enzymogenes, mainly considering the factors of temperature, revolving speed and duration of shaking flask. The result showed that at 28℃,200 rpm and shaking for 60 h when the output was the largest. Finally, the stimulating factor experiment was carried out, choosing the polysaccharide of Fusarium graminearum which was the target biological of L. enzymogenes as a stimulating factor to observe its effect on HSAF. Due to limited experimental conditions, we only get a small amount of crude polysaccharide, the experimental results shown that adding stimulating factor had a negatively affect of HSAF production.To proving the effects of the fermented products of L. enzymogenes on the diseases directly. The products fermented by optimized methods were heated at 65℃ and concentrated to dryness after absorbed by an inertia powder, its effects on several important crop diseases were tested by plate assay and potted or field crop plants inoculated. The results from plate showed that EC50 of mycelia growth inhibition on Magnaporthe oryzae, Rhizoctonia solani and Fusarium graminearum were 2.1326,2.1457 and 3.6959 μg/mL respectively calculated with the quantity of HSAF, and EC50 of F. graminearum spore germinating inhibition was 12.2587 μg/mL. Treated with the powder dissolved before the pathogen inoculated, the ratio of the fermented with HSAF at 10.24 μg/mL prevented wheat against wheat powdery mildew was 58.15% after 22 d, on the other hand, that of tridimefons at 150 μg/mL was 45.93%. The results of the field test in 2013 indicated that the fermented was better than carbendazim in controlling on wheat gibberellic disease:even though the preventive and curative effects of fermented at 96.0 g in HSAF/hm2 were both just over 20% at 14 d after treatment, but that of carbendazim at 1110.0 g/hm2 were 13.39% and 12.00% respectively. The results of the field test in 2014 indicated that under the natural infection situation, the ratio of the fermented with HSAF at 1.53 μg/mL prevented wheat against wheat gibberellic disease was 76.40% after 28 d which is better than that of the contrast of 30% benzyl-propiconazole missible oil 300.0 mL/hm2. In conclusion, the fermented products of L. enzymogenes could be used to control several important crop diseases as a biogenic natural product pesticide. |
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