Antagonistic Potential of Bacillus velezensis and Sericin-Based Nanomaterials Against Mulberry Root Rot Pathogens

Root rot disease in mulberry is primarily caused by the fungal pathogens Lasiodiplodia theobromae and Rhizopus sp., posing a significant threat to sericulture fields. The present study aimed to isolate bacteria from the rhizosphere of root-rot-affected mulberry plants and to evaluate their antagonistic potential against these fungal pathogens. Furthermore, the study assessed the biocontrol efficacy of bacterial crude metabolites in combination with sericin nanomaterials. Two pathogenic fungi and seven bacterial isolates were obtained from diseased roots and rhizospheric soil. The antagonistic activity of the isolates was initially screened against the target pathogens using the dual-culture technique. The most potent bacterial strain, isolated from the mulberry rhizosphere in Karnataka, was identified as Bacillus velezensis through 16S rRNA gene sequencing and phylogenetic analysis. Bacillus velezensis exhibited strong antagonistic activity against the root rot pathogens L. theobromae and Rhizopus sp., achieving mycelial growth inhibition of 64.79% and 35.38%, respectively, compared to the control (p < 0.05). Furthermore, sericin nanomaterials were synthesized and characterized using Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, X-ray Diffraction, and Fourier Transform Infrared Spectroscopy to confirm their nanoscale size, elemental composition, and functional groups. The in vitro study demonstrated that sericin nanomaterials, in combination with bacterial crude extracts, exhibited high inhibitory potential against fungal mycelial growth. This approach represents a promising eco-friendly strategy for the effective management of mulberry root rot pathogens.