A Novel <i>Trichoderma semiorbis</i> Strain FJ059 Exhibiting Sclerotium‐Mycoparasitic Ability and Biocontrol Potential to Southern Blight Caused by <i>Sclerotium rolfsii</i>

ABSTRACT Sclerotia produced by Sclerotium rolfsii , the causal agent of southern blight in many plants, can survive in the soil for many years, making the disease difficult to control. In this study, Trichoderma species were screened for their mycoparasitic ability against the sclerotia of S . rolfsii . Through dual culture between Trichoderma and S . rolfsii , FJ002, FJ059 and NM082 showed strong inhibition ability, with inhibition rates of 100%, 100% and 86%, respectively, significantly different from other strains. The sclerotium‐mycoparasitic ability of these three strains was tested on potato dextrose agar (PDA) plates, on the soil surface and within the soil. Strain FJ059 exhibited the strongest sclerotium‐mycoparasitic ability, killing 80% of sclerotia on PDA plates after 10 days and all of the sclerotia on the surface of the soil and inside the soil after 15 days. The sclerotia inoculated by Trichoderma semiorbis FJ059 labelled by GFP were sliced and observed using a fluorescence microscope, further confirming that FJ059 could parasitise the sclerotia of S . rolfsii . A greenhouse experiment with pepper seedlings demonstrated the control effect of FJ059 on S . rolfsii . The pepper seedlings treated with FJ059 and S . rolfsii had no signs of disease, better than treatment with tebuconazole. The results indicate that FJ059 has a significant control effect on southern blight caused by S . rolfsii . This is the first report of T . semiorbis showing sclerotium‐mycoparasitic ability against S . rolfsii . This strain may be a potential agent to control southern blight caused by S . rolfsii .