Abstract: Trichoderma harzianum has a strong biological control effect on plant diseases. However, there are significant differences in the level of solid state fermentation among different microbial strains. In order to obtain the best optimization conditions for solid state fermentation of T. harzianum BWT1.221 which has the biocontrol function against plant pathogens and will be applied in agricultural production, single factor and orthogonal experiments were used to optimize different material composition and fermentation conditions of T. harzianum BWT1.221 solid state fermentation by measuring number of cells and the proportion of T. harzianum before and after drying in this study. The results showed that the optimum fermentation material composition of T. harzianum BWT1.221 with solid fermentation was that the mixture of bran and corn meal which were used as fermentation substrate. The optimum material propotion was about bran: corn meal = 0.25:1. The addition of sucrose as a available carbon source was 5%. The content of available nitrogen source urea and ammonium sulfate was 0.15% and 0.8%, respectively, and the ratio of material to water was 1:0.7. The results of optimal fermentation conditions for solid state fermentation showed that the fermentation temperature was 28℃, the fermentation time was 7 d, the liquid inoculum volume was 5%, and the microbial inoculum was dried at 28 ℃ for 24 h. Microbial agent was prepared by the above method, the number of cells were 10.78×10⁹ CFU/g and the pollution rate of other microorganisms was less than 0.01%. This study provided technical support for the large-scale fermentation production of T. harzianum, which has important significance for promoting the application of biocontrol agents to control plant diseases and reduce environmental pollution.

Key words: Trichoderma harzianum, solid state fermentation, number of cells, the proportion of T. harzianum before and after drying, microbial agent