Biocontrol Efficiency of Endophytic Fungi Against Stem-Rot in Cymbidium goeringii

Cymbidium goeringii, an important orchid species, holds significant aesthetic and commercial potential in horticulture. However, stem rot caused by Fusarium oxysporum has emerged as a major biological constraint hindering industry development. In this study, we isolated five endophytic fungal strains from C. goeringii roots-namely, DG3 (Bjerkandera), DG4 (Cylindrocarpon), CLG3 (Talaromyces), CLG6 (Clonostachys), and Z3 (Trichoderma)-and assessed their inhibitory efficacy against stem rot and their potential to promote growth in C. goeringii. In vitro assays indicated that all five fungal strains had the ability to fix nitrogen and produce indole-3-acetic acid, as well as the capability to produce protease and exert broad-spectrum antimicrobial effects. The five endophytic fungal strains exhibited stem rot-resistant effects, among which strain Z3 showed the best inhibitory effect against stem rot, with a control efficacy reaching 68.89%. Treatment of C. goeringii seedlings with these endophytic fungal fermentation broths for 100 d significantly promoted growth compared to the control. The fresh weight increased by 10.53% to 88.16%, and root activity was enhanced by 50% to 162.5%. Additionally, the plant height and the longest leaf length increased by up to 23.68% and 47.50%, respectively, compared to the control. Additionally, the total chlorophyll content was up to 25.34% higher than that of the control group, and the soluble protein content was up to 39.54% higher. The MDA content was reduced by up to 40.23% compared to the control group. These endophytes also regulated the activity of defense-related enzymes in C. goeringii, including delaying the decline in the activities of antioxidant enzymes such as superoxide dismutase, peroxidase, and catalase. These results highlight the potential of these five endophytic fungi as effective agents for managing stem rot in C. goeringii.