Spore production in the solid-state fermentation of stevia residue by Trichoderma guizhouense and its effects on corn growth

Trichoderma is an important and widely used plant growth-promoting fungus (PGPF). In this study, stevia residue amended with amino acids hydrolyzed from animal carcasses was used for the production of Trichoderma guizhouense NJAU 4742 by solid-state fermentation, and then its potential to promote corn plant growth was evaluated in combination with chemical fertilizer (CF) or organic fertilizer (OF). The highest spore number of 7x10(9) CFU g(-1) fresh weight was obtained under the following optimal parameters: material ratio of 50% (stevia residue:rice bran=1:1), pH value of 3.0 (amended with 6.67% amino acids), initial moisture content of 60%, inoculum size of 10%, material thickness of 3 cm and an incubation time of 4 days. The aboveground corn plant biomass obtained with T. guizhouense applied alone and with CF treatments were slightly higher than those of no fertilizer control and CF treatments, respectively. However, T. guizhouense applied with OF significantly (P<0.05) increased aboveground biomass compared to OF and yielded the highest aboveground biomass among all the treatments. Moreover, T. guizhouense applications primarily influenced the fungal bulk soil community composition, among which three OTUs (OTU_2 and OTU_9 classified as Chaetomium, and OTU_4 classified as Trichoderma) were stimulated in both bulk and rhizosphere soil. Notably, a specific OTU_3 (Phymatotrichopsis) was only stimulated by T. guizhouense applied with OF, possibly leading to high soil productivity. These results show that it is feasible to employ stevia residue in the eco-friendly fermentation of T. guizhouense, which is strongly suggested for enhancing OF applications.