Biocontrol Potential of Indigenous Trichoderma Isolates Against Sclerotium rolfsii Causing Southern Blight of Pepper in Ogun State, South West Nigeria

Southern blight caused by Sclerotium rolfsii is a destructive soilborne disease of pepper (Capsicum annuum) in South West Nigeria, where warm moist soils support the survival and spread of sclerotia across cropping seasons. Biological control using indigenous Trichoderma isolates adapted to local soil conditions presents a promising environmentally acceptable alternative to chemical fungicides. This study evaluated the in vitro and in vivo biocontrol efficacy of 18 Trichoderma isolates obtained from rhizosphere soils of pepper farms in Ogun State against S. rolfsii. Isolates were characterised molecularly using ITS and tef1 gene sequences and evaluated for antagonistic mechanisms including mycoparasitism, antibiosis, and volatile compound production. In vitro dual culture assays demonstrated that 11 of 18 isolates inhibited S. rolfsii mycelial growth by more than 60 percent, with three isolates identified as T. asperellum and T. atroviride showing the greatest inhibition. In vivo greenhouse trials confirmed that T. asperellum isolate TRI-OG7 reduced southern blight incidence by 72 percent and sclerotial viability by 84 percent in artificially infested soil. Field trials at two locations confirmed a 61 percent reduction in disease incidence and a 28 percent yield advantage over untreated controls. Mechanistic studies identified cell wall-degrading enzyme production and antibiotic volatile compound emission as the primary antagonistic mechanisms. The study establishes TRI-OG7 as a strong candidate for development into a commercial biocontrol formulation for use in South West Nigerian pepper production. Keywords: Trichoderma, Sclerotium rolfsii, biocontrol, pepper, Ogun State.