Objective A Trichoderma species in Paeonia delavayi rhizosphere soil with growth-promoting effect on the plant was isolated and identified.

Methods Potential strains were isolated and screened by morphological and molecular biological methods. A fungus, coded 15-9, was assessed for its phosphorus solubilization, nitrogen fixation, and siderophore production capabilities. Specific symbiotic effects of the isolate on the growth, biomass, chlorophyll content, and resistance-related physiological and nutritional indexes of P. delavayi seedlings were determined.

Results The isolated 15-9 capable of dissolving phosphorus, fixing nitrogen, and producing siderophores was identified to be Trichoderma koningiopsis. Six months after inoculation of the isolate, the acid phosphatase activity in the roots of P. delavayi seedlings and rhizosphere soil were 0.53U·g⁻¹ and 723.41U·g⁻¹, representing 26.19% and 124.85% increases over those of control, respectively. The available phosphorus and total nitrogen contents in the rhizosphere soil increased by 82.04% and 42.86%, respectively, while the total iron in the plants rose 143.13% over control. The plant height, leaf count, main-root length, underground part diameter, and whole plant dry and fresh weights of the seedlings were 64.80%, 86.53%, 20.10%, 16.16%, 37.00%, and 41.01%, respectively, higher than those of control. And the total chlorophyll in the leaves reached 0.56mg·g⁻¹, which was 116.16% higher than that of control. Furthermore, the POD, SOD, and CAT activities and the contents of MDA, soluble protein, and soluble sugar in the leaves and roots rose significantly as well. Among them, The SOD activity of 819.35U·g⁻¹ in the leaves and 7,212.43U·g⁻¹ in the roots were 4.84 times and 8.42 times, respectively, and CAT of 343.75U·g⁻¹ in the leaves and 324.25U·g⁻¹ in the roots, 4.45 times and 11.15 times, respectively, of those of control. Meanwhile, the 56.00% colonization on the roots of the isolated fungus indicated that a stable symbiosis in the rhizosphere could be expected.

Conclusion T. koningiopsis as identified in the study exhibited significant growth promoting effect on P. delavayi seedlings. It could colonize the root system at a rate to significantly promote growth and development as well as disease resistance of the plant.