Soybean Root Rot Biocontrol Strain Identification And Optimization Of Fermentation Conditions,

To classify taxonomy of strain HNDF2 and research its biological control to soybean root rot, it was identified with morphological and physiological properties and the fermentation condition was optimized and inhibition experiment to soybean root rot pathogen were contrived.The biocontrol effect of the fermentation liquid of Bacillus laterosporus BL-21, HNDF2 strain and the mixture of two bacteria with 1:1 were compared to fermentate, the result was showed that three fermentation liquid all had biological control effect to four pathogenic fungi caused soybean root rot. In dual cultures experiment, HNDF2 strain liquid showed rivalry to Fusarium oxysporum, Fusarium graminearum, Rhizoctonia solani and Fusarium moniliforme, the rivalry effect were 60.61%,27.5%, 91.20% and 54.67% separately; In shake flask culture, strain HNDF2 demonstrated satisfactory inhibitory effection to four pathogenic mycelium growth, the inhibition effect were 26.23%,23.86%,53.82% and 67.62% separately.The experiment on soybean germination and test-tube seedling presented that all of three fermentation liquid had effective promotion on soybean offspring growth. Through affection of strain HNDF2 fermentation liquid, the soybean seeding high was increased 21.49% while root length was increased 18.27%.The greenhouse pot experiment showed all of three fermentation liquid can efficiently decrease disease severity of soybean root rot, disease index were 65.56, 68.89 and 69.17, respectively and the biocontrol effect were 28.48%,24.85% and 24.54% respectively. There existed remarkably discrepancy compared with control.Lots of physiological index of soybean treated by fermentation broth of HNDF2 were conspicuous improved, such as root length, root dry weight, nodule quantity, bean pods quantity and the weight of one hundred grain. Individual thallus morphous, cultivation feature, physiological and biochemistry feature of strain HNDF2 were observed and tested through traditional methods.16S rDNA molecular biology identification methods were also adopted. The result of taxonomy identification showed that strain HNDF2 was Bacillus subtilis.Single-factor test and response surface methodology were adopted to find the optimized medium prescription of strain HNDF2. The result of single-factor test showed that glucose was the optimal carbon source, peptone was the optimal nitrogen source, Mn2+, Ca2+and K+ were added to improve inhibition effect on root rot pathogen. According to response surface methodology analysis, the optimized medium prescription was determined as follows:Glucose was 9.64g/L, Peptone was 12.15g/L sodium chloride was 4g/L calcium carbonate was 2.44g/L, potassium dihydrogen phosphate was 0.2g/L, manganese sulfate was 0.5g/L. Antifungal experiment of fermentation liquid of strain HNDF2 fermented with the optimized culture prescription showed that the colony diameter of pathogenic fungi was 17.43mm, extremely closed to the predictive value. It indicated the optimized model was reliability.Single-factor test was applied to find the suitable fermentation condition of strain HNDF2, the best fermentation condition was determined as follow: temperature was 34℃, fermentation time was 48h, pH was 7.5 and ventilatory capacity was 50mL/250mL.The inhibition effect of fermentation liquid cultured with the optimized fermentation condition improved 46.35%, and was superior to that of primitive conditions.