| This study was aimed at isolating and screening antagonistic bacterial strains,identifying their taxonomy,and evaluating their biocontrol potential.Results were obtained as follows:1.Plant growth-promoting strain AW-17 and CanL-30 were selected.A total of 82 strains were obtained from Hubei province(Wuhan,Xianning)and Anhui province(Wuhu),including bacteria and yeasts.Furthermore,two effective bacterial strains,namely AW-17 and CanL-30,were screened for plant growth promotion based on the results from the microbia-plant co-culturing experiment and seed germination experiment.The result revealed that these two bacteria strains could promote plant growth through production of volatile organic compounds(VOCs).Besides,strain AW-17 also have the abilities to produce Indole-3-acetic acid(IAA)and solubilize phosphate.These two bacteria were also chosen for in vitro potting experiments but only strain AW-17 has shown potential plant growth promoting effect.2.The classification properties of the strain AW-17 and CanL-30 were identified.Strain AW-17 formed viscous colonies with creamy yellow color and smooth texture under 8~35°C.The optimum growth temperature range was optimizing about 20°C~30°C,and they can grow well under the 7% salinity condition,but are unable to grow in the 10% salinity condition.Strain AW-17 was gram-negative and failed to produce any spores.The results of the physiological and biochemical assays and 16 S rDNA sequence analysis showed that the strain AW-17 belonged to Serratia liquefaciens.On the other hand,colony morphology of the strain CanL-30 was milky white,texture smooth.It can grow under the condition of 15 to 40? with the optimum growth temperature ranging from 20°C to 30°C.Similar to strain AW-17,it grew under 7% salinity condition,but failed to grow in the 10% salinity conditions.It is gram-positive and produces spores.Identification results showed that the strain CanL-30 belonged to Bacillus subtilis.3.The antagonistic bacteria CanL-30 were screened and the antifungal metabolites were purified.Antagonistic strain Bacillus subtilis CanL-30 was selected based on dual culturing and in vivo test,and it showed high efficacy in suppression of various pathogens through production of antifungal metabolites.The physical and chemical properties of the crude extract from the cultures of CanL-30 were analyzed,and the crude extract compounds were proved containing iturin.The metabolite produced by CanL-30 fermented in NB medium for 72h(28°C,150 r/min)could have a better antifungal effect,with antifungal rate of 90% and the antifungal metabolites were extracted by using the method of acid precipitation methanol extraction,poisoned test results show that the different concentration of crude extract on gray mold all have different degrees of inhibition,and 365 g/mL of the crude extract has a great inhibition in Botrytis cinerea,with inhibition rate of 100%.The Canl-30 antifungal crude extract has the characteristics of high-temperature resistance and ultraviolet resistance and when it put in 100? water bath pot after 60 min,it showed no difference in antifungal activities compared with control.Besides,when it exposed to UV lamp(UV-C,30W)for 150 min,there still was no significant difference in inhibition zone compared with control.The active substance in the crude extract was isolated and identified,and it was found that the metabolites produced by CanL-30 contained iturin.The results of these study laid a solid foundation for deeper development of these two strains in practical use. |
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