Objective  Trichoderma strains antagonistic to stem rot pathogens were studied to develop a biocontrol agent for the disease on Anoectochilus roxburghii.

Method From the A. roxburghii plants grown under simulated wild conditions, strains of Trichoderma were obtained by tissue isolation and classified by morphological observations and homology analysis with ITS and rpb2 sequences. Ability of the isolates to resist stem rot was evaluated in vitro by the plate confrontation method. Growth of A. roxburghii in the presence of the identified strains was monitored.

Results  The resistant A21B-1, A21B-2, and A21E strains were isolated and subsequently identified as T. rugulosum, T. koningiopsis, and T. longifialidicum showing the inhibition rates of 75.29%, 73.55%, and 60.02%, respectively, on Fusarium oxysporum f. sp. opponiarum ASP01. Furthermore, 15 d after a T. rugulosum inoculation in an indoor control evaluation test A. roxburghii exhibited a significant inhibition rate of 91.9% against the stem rot. That suggested a potentially effective means for control on the disease. In addition, the 3 strains displayed a significant growth promoting effect on the A. roxburghii seedlings in a greenhouse with increased plant weight, height, stem diameter, leaf area, and SPAD value in 6 months. Among them, T. koningiopsis and T. longifialidicum not only significantly increased the plant biomass over control by 58.68% and 58.99% and leaf area by 66.82% and 59.73%, respectively, but also elevated the contents of functional polysaccharides and kinsenoside with the greatest increases of 89.62% on polysaccharides and 11.83% on kinsenoside by T. koningiopsis.

Conclusion Three strains of Trichoderma demonstrated in vitro a significant antagonistic effect against the stem rot disease on A. roxburghii. Their presence also significantly promoted the growth and increased the functional polysaccharides and kinsenoside contents in the plant.