Study On Liquid Fermentation Technology And Effects On Disease-control & Growth-promotion Of Biocontrol Bacteria Strain A

Plant disease is a formidable enemy to agriculture production, and about more than eighty percent of plant diseases were caused by fungal pathogen. Nowadays these plant diseases were mainly controlled by chemical germicide. But more and more evidences showed that chemical germicide had many negative problems, such as polluting environment, bringing about drug-fast problems and so on. Using biological means or exploiting biological germicides instead of chemical germicide were considered to settle these problems.This study tried to make bacteria strain A an efficient biological germicides. Therefore, this experiment mainly focused on study of liquid fermentation technology and effects on disease-control & growth-promotion of biocontrol bacteria strain A. The results showed as follows.Antagonistic effects of fermentation broth of strain A were tested using sandwich method, filter paper slip method, stiletto method, intermixing-stiletto method and so on. Advantages and disadvantages of these methods were compared, and finally ascertained a new method of double deck-stiletto method which was used to test antagonistic effects of fermentation broth in the following experiments.The optimum culture media of strain A was screened from six different media. The components of the optimum media (YDC) were composed of glucose 20 g, yeast extracts 10 g, CaCO₃ 20 g, water 1000 mL. The optimum condition of shake-flask culture was ascertained as follow: culture temperature 35℃, capacity of shake-flask 12%, capacity of inoculum 3%, initial pH value 7.2.Based on the optimized optimum media and shake-flask culture conditions, batch fermentation and feeding batch fermentation were carried out. The best culture media suited fermentation and the best time to feed culture media were obtained. Spores concentration of fermentation broth could reach to (3.41±0.151)×10⁹ per milliliter.Fermentation broth obtained from fermenter cultivation was centrifuged, then the wet thalli were mixed with CaCO₃. The mixture was desiccated 30 minutes in vacuum drier to powder as biocontrol bacteria powder of strain A. Temperature had little influence on storage of the biocontrol bacteria powder. The survival rate of spores could kept about 60% and concentration of spores kept more than 10¹¹ cfu/g after the powder was storaged for 180 days under 4℃, 25℃, 37℃respectively.The strain A powder was applied to the study of controlling plant diseases. The results showed that it had efficient control effect against Humicola Traaen on peach treatment and a higher disease control effect and growth promotion on cucumber treatment. Peach inoculated with suspension of strain A by means of stabbing in advance showed a higher control effect above 90% against Humicola Traaen after pathogen inoculated 4 days; and peach inoculated with suspension of strain A by means of sprinkling showed a natural control effect about 55.94%, and the biocontrol bacteria strain A could inhabit on the surface of peach. Soaking cucumber seeds with suspension of strain A could promote growth of bud 19.42%. Seeds treated with strain A by means of soaking and seed dressing beforehand, cucumber showed evident enhances than control group treated with water in the aspects of height, weight and survival rate, and the increases were 62.26%, 56.61%; 35.61%, 37.67%; 8.2%, 8.85%, respectively. Unorganized cucumber leaf showed high control effect of 77.92% with treatment of seed dressing. Potted cucumber seedlings treated with strain A showed high control effect against Colletotrichum Lagenarium after pathogen inoculated 14 days, and the highest control effect was 49.69% with the treatment of irrigation.Through the experiment of cute oral toxicity of biocontrol bacteria strain A, no one death case was observed, which showed that the strain A had slight toxicity.