Abstract: [Objective] The Zanhuang jujube (Ziziphus jujuba 'Zanhuang')fruit black rot disease is one of the most serious fungal pathogens in China. Bio-control of the disease is of great significance to the fruit green production and its sustained efficacy as well as being free of fungicide pollution. The objective of the present study is to screen out a Streptomyces strain with good inhibitory effect against the fungal disease pathogen (Alternaria tenuissima) and optimize the fermentation medium formula, as well as fermentation conditions with the purpose of laying a foundation for field experiment and the development of bio-control agent.[Method]The agar block method, the Oxford cup method and the medicated plate method were applied in the multiple screening in vitro of 10Streptomyces strains against A. tenuissima, which were originally isolated from special habitats. The optimum fermentation medium and conditions for the selected strain were determined by using a quadratic orthogonal rotation combination design and a single-factor experiment design, respectively.[Result] During in vivo experiment, strains AC03, AC04 and AC07 showed significant antagonistic effect, their diameter of inhibition zone being (32.09±1.45)mm, (15.75±1.34)mm and (18.33±0.78)mm respectively. The fermentation filtrate activity test of the three strains demonstrated that the strains AC03 and AC07 had a diameter of inhibition zone of (20.94±0.92)mm and (23.44±1.63)mm respectively,while the strain AC04 had a diameter of only (14.5±0.71)mm. The further conducted test of the inhibition effect of the fermentation filtrates of the strain AC03 and AC07 on mycelial growth displayed that the antagonistic substance produced by the strain AC07 had a better and longer inhibition effect than that produced by the strain AC03. These tests demonstrated that of the 10 isolates, the strain AC07 had the best inhibition effect on A.tenuissima, that is the main cause of the black rot disease on Zanhuang jujube. The optimum fermentation medium for the strain AC07 consists of maltose, 5.7%; soybean meal, 2.7%; (NH₄)₂SO₄, 0.17%; CaCO₃, 0.22%; NaCl, 0.17% and Yeast Powder, 0.2%. The optimum fermentation conditions were defined as follows:concentration of seed broth, 1.5×10⁷~2.0×10⁸ cfu·mL^-1, inoculation amount, 2% (V/V), the volume of media, 40 mL, in a 250mL flask initial pH at 7.0, fermentation temperature 28℃ and fermentation time 108 h.[Conclusion] The strain AC07 was selected as a new antagonistic Streptomyces for developing biocontrol agent against the Zanhuang jujube fruit black rot disease. The optimization of its fermentation medium and conditions increased the production of the target metabolites, laying a good foundation for further research and development.

Key words: Zanhuang jujube, black rot disease, antagonistic Streptomyces, screening, fermentation conditions