Effect of Rhizospheric Fungus on Biological Control of Root Rot (Fusarium equiseti) Disease of Saposhnikovia divaricata

Saposhnikovia divaricata is a high-demand medicinal plant containing various bioactive metabolites (e.g., chromone). However, root rot disease leads to a dramatic reduction in the yield and quality of S. divaricata. The use of rhizospheric microorganisms is one of the best strategies for biological control. In this study, a total of 104 fungi isolated from the rhizospheric soil of S. divaricata plants were examined for their different antifungal properties. Subsequently, strain MR-57 was selected as a potential stock for biocontrol due to its broad-spectrum antagonistic activity against pathogens, including F. equiseti. Based on the analysis of morphological properties and rDNA internal transcribed spacers (ITSs), strain MR-57 was identified as Acrophialophora jodhpurensis (GenBank No. OK287150.1), a newly recorded species for China. In an in vitro antifungal assay, the culture filtrate of strain MR-57 significantly reduced the conidial germination rate and induced alterations in the mycelia morphology of F. equiseti, such as deformation and degradation. To assess the antifungal efficacy of MR-57 against root rot disease and the properties promoting the growth of S. divaricata, pot experiments were performed under natural outdoor conditions. The results indicated that co-inoculation with MR-57 delayed the occurrence of S. divaricata root rot and showed a control efficacy of 65.41% (p < 0.05) based on the measurement of suppressed disease lesions. Additionally, MR-57 successfully colonized and formed a stable population in the soil in which S. divaricata was grown, and it exhibited a consistently positive effect on the promotion of the growth of S. divaricata plants. In short, Acr. jodhpurensis MR-57 could be considered for the development of a potential biocontrol agent for the management of S. divaricata root rot caused by F. equiseti.