Isolation And Identification Of Antagonistic Actinomycetes Against Leaf Blight Pathogens Of Schisandra Chinensis And The Optimization Of Its Fermentation Conditions

Leaf blight which caused by Alternaria tenuissmia is a fungal disease and one of the main disease in Schisandra chinensis. This disease mainly harm parts for blade and lead to defoliation, abscission of fruits, decrease of fruit quality and production of Schisandra chinensis. Using chemical pesticide to control the diseases is principal pathway in agriculture nowadays. However, as the higher requirement of people for for quality of medicinal materials, chemical pesticide resistance, persistent and environmental pollution will become a difficult question.Actinomycetes, as a biological pesticide exist widely in nature. The secondary metabolites antibiotics of strains can affect on some pathogenic bacteria. In this paper, Isolation and Identification of antagonistic actinomycetes against leaf blight pathogens of Schisandra chinensis and the optimization of its fermentation conditions and its biocontrol efficacy were researched.1. The pathogen Alternaria tenuissmia was separated from typical leaf blight of Schisandra chinensis from Ji?an and was identified by Koch’s rules. The biological characteristics results showed that mycelia grew faster and spore generated more in medium PDA and PDBA. Fructose and peptone were the best carbon source and nitrogen source for the pathogen. Dark condition was significantly beneficial for spore generation and light condition was beneficial for mycelia growth. pH 5-7 was most suitable for the pathogen. The optimum temperature for mycelia growth and spore generation was 25℃. Deadly temperature for the spore was 54℃.2. Twenty-seven actinomycetes strains were screened from rhizosphere soil of Schisandra chinensis. Two strains(A-25-8 and A-38) had high antagonistic effects against leaf blight pathogen and their inhibition rate was 66. 26% and 66. 10% by three line method,respectively. Strains A-25-8 aimed at leaf blight, and strains A-38 had a broad-spectrum inhibitory action to against more pathogen of Schisandra chinensis and Ginseng. None of the pathogen had the capacity for growth when mixed A-25-8 and A-38 strains or antibacterial activity of fermentation filtrate.3. A-25-8 strain had the better inhibitory effect on leaf blight disease. A-25-8 strain growed in wound of the blade surface. It can effectively inhibit the growth of leaf blight pathogen. Treatment experiment of A-25-8 and control effect of A-38 were relatively weak. They can control the leaf blight infection to a certain extent: both of the controlling effects were more than 50% control effect more than 50%.4. Two actinomycetes strains were identified based on its 16 S rRNA sequence, together with the morphological, physiological and biochemical characteristics. The antagonistic actinomycetes A-25-8 was identified as Streptomyces anulatus. The A-38 appeared a sister lineage to Streptomyces lactacystinicus.5. The optimum fermentation conditions for the strain A-25-8 were as follows: PD culture medium; carbon sources, glucose; nitrogen sources, KNO3; pH, 7.5; temperature, 28℃; culture time, 3d; inoculation amount 10%(v/v) and rotational speed, 160r/min. The activity and stability experiment of antagonistic bacteria A-25-8 showed that the antimicrobial activity of the fermentation filtrate decreased when the ultraviolet irradiation time was prolonged and the ambient temperature was increased; the antibacterial activity of fermentation filtrate decreased with the acid-base concentration increased. At room temperature, with the increase of storage time, the fermentation filtrate activity gradually reduced.