Optimization of solid fermentation process of three Trichoderma strains with plant growth-promoting effects

Abstract:

[Background] Trichoderma is a kind of fungus widely distributed in nature, which produces a variety of enzymes and secondary metabolites, showing many benefits including promoting plant growth, improving soil fertility, and antagonizing various soil-borne pathogens. [Objective] To optimize the solid fermentation conditions of three plant growth-promoting fungi (Trichodermalongibrachiatum MD30, T. citrinoviride JS84, and T. guizhouense NJAU4742), the effects of different fermentation conditions on the spore production of Trichoderma spp. were explored to provide references for Trichoderma spp. production. [Methods] In this study, the spore production of three Trichoderma spp. under different fermentation conditions was measured and optimized by the single factor experiment and the response surface methodology. The effects of the addition of nitrogen source, initial pH, material thickness, inoculation amount, and temperature on solid fermentation were analyzed. [Results] The single factor experiment showed that the optimal fermentation temperature of T. longibrachiatum MD30, T. citrinoviride JS84, and T. guizhouense NJAU4742 was 28 ℃, and the optimal amount of Trichoderma liquid inoculum was 10% with 3.0 cm material fermentation thickness. However, the optimal initial pH of the material and the addition amount of amino acid hydrolyzate were different among these three strains. In detail, the optimal initial pH value of T. longbranchus MD30 and T. guizhouense NJAU4742 for solid fermentation was 5.0, while that of T. citrinoviride JS84 was 3.0. The optimum amino acid hydrolyzate addition amount for solid fermentation of T. longbranchus MD30 and T. guizhouense NJAU4742 was 10%, while that of T. citrinoviride JS84 was 5%. Based on the experimental analysis, the initial pH, material thickness, and temperature were selected as three top important factors in the determination of the spore production. Therefore, the optimal fermentation conditions for solid fermentation of these three strains were obtained based on the response surface analysis. The optimal conditions for solid fermentation of T. longbranchus MD30 were the initial pH value of 5.0, the material thickness of 3.0 cm, and thetemperature of 27.4 ℃. Under this optimized condition, the number of spores per gram dry weight of the solid fermentation product was as high as 6.3×10⁹ CFU. The optimal conditions for solid fermentation of T. citrinoviride JS84 were the initial pH value of 3.0, the material thickness of 3.0 cm, and the temperature of 28.8 ℃. Under this optimized condition, the number of spores per gram dry weight of the solid fermentation product was as high as 6.9×10⁹ CFU. The optimal conditions for solid fermentation of T. guizhouense NJAU4742 were the initial pH value of 5.0, the material thickness of 3.3 cm, and the fermentation temperature of 26.7 ℃. Under this optimized condition, the number of spores per gram dry weight of the solid fermentation product was as high as 5.1×10⁹ CFU. [Conclusion] Response surface optimization experiment improves the experimental efficiency, increases the spore production of Trichoderma spp., reduces the production cost, and is conducive to field application and commercial production of bacterial agents.