Advanced Biocontrol Strategies Utilizing Bacillus Species for Sustainable Suppression of Sclerotinia sclerotiorum, Sclerotinia minor, and Rhizoctonia solani in Agroecosystems

Abstract

This study evaluated the antagonistic activity of Bacillus isolates recovered from soil, corn (Zea mays) rhizospheres, Taraxacum officinale, and sclerotia against three major soilborne fungal pathogens: Sclerotinia sclerotiorum, Sclerotinia minor, and Rhizoctonia solani. Antifungal activity was assessed using dual-culture and culture-filtrate assays evaluating both filter-sterilized and autoclaved filtrates for thermal stability and their effects on fungal growth and sclerotial formation. Among the evaluated isolates, SSB5 demonstrated broad-spectrum antagonistic activity in dual-culture assays, effectively inhibiting mycelial growth across all three target pathogens and suppressing sclerotial development. Isolate BS1 demonstrated selective antagonistic activity, displaying moderate direct inhibition against Sclerotinia minor (13.0 mm zone) while lacking activity against S. sclerotiorum and Rhizoctonia solani. Culture-filtrate assays revealed strain- and thermostability-dependent bioactivity; untreated filtrate of isolate BS3 exerted sustained 100% mycelial growth arrest against S. sclerotiorum across 10 days, while retaining moderate heat stability after autoclaving (80.94% at Day 5). Additionally, autoclaved filtrates of BS3, SSB5, and SSB6 induced complete suppression (100%) against S. minor at Day 5, though heat-treated SSB5 and SSB6 completely lacked activity (0%) against S. sclerotiorum. These findings demonstrate that Bacillus isolates, particularly BS3, possess strong antagonistic activity against important soilborne fungal pathogens and highlight their potential as sustainable biocontrol agents for integrated disease management. Offering environmentally friendly alternatives to conventional chemical fungicides.