Abstract

Fungal diseases in plants are a key threat to global food security, causing huge crop losses.  Bacterial biofungicides antagonize several fungal phytopathogens, controlling plant diseases. Despite several bacterial species reported as biofungicides, indigenous Bacillus species from Nepal have yet to be explored for their antifungal activity, so that they could be used as efficient biofungicides to enhance agricultural production. In this study, we identified 65 isolates of Bacillus based on cultural, morphological, and biochemical characteristics from soil, phylloplane, and dead insects. Preliminary antifungal activity against three fungi, Fusarium spp. Curvularia spp. and Aspergillus spp. by dual culture method showed that 16 (26.67%), 3 (5.00%), and 22 (36.67%) isolates of Bacillus species exhibited inhibition against Fusarium spp., Curvularia spp., and Aspergillus spp., respectively. Subsequent leaf disk assays on cucumber plants demonstrated 34 (56.67%) isolates of Bacillus species exhibiting significant suppression of powdery mildew fungi (Erysiphe cichoracearum). Notably, two isolates (NS116, NS114) exhibited the maximum antifungal activity and were characterized by 16S rRNA gene sequencing as Bacillus cereus strains. B. cereus demonstrated a higher ability to control fungal diseases with a preventive effect exceeding 90%, compared to 3% Anvil (4.8% w/w Hexaconazole), which displayed only a 67.81% preventive effect. Since Anvil induces ecological impact due to its toxicity to aquatic invertebrates and fishes, effective bacterial pesticides like Bacillus species could be a better choice. These findings highlight the potential of Bacillus spp. as potent biocontrol agents, due to their ability to produce antifungal compounds and manage fungal pathogens.