Development of Wettable Powder Formulation of Bacillus subtilis and Its Biological Control Against Fungal Phytopathogens

Microbial biocontrol agents often exhibit limited shelf life, which restricts their commercialization, storage, and large-scale agricultural application. In this study, freeze-drying (FD) microencapsulation was evaluated as a strategy to improve the stability of a wettable powder (WP) formulation based on Bacillus subtilis fermented broth using maltodextrin (MD) as a carrier. The physicochemical, structural, morphological, and antifungal properties of the resulting formulation were characterized. Physical characterization revealed complete solubility (100% at 0.1 g mL−1), rapid wettability (2 s), and low hygroscopicity (3.86%), indicating favorable properties for handling and application. Scanning electron microscopy revealed irregular glass-like particles of different sizes, while Fourier transform infrared spectroscopy indicated the distribution of components within the maltodextrin matrix. The antifungal activity of the WP and the effects of its volatile organic compounds (VOCs) were evaluated against the phytopathogenic fungi Fusarium oxysporum, Fusarium solani, Fusarium graminearum, Rhizoctonia solani, and Sclerotinia sclerotiorum. The formulation inhibited fungal growth within the tested concentration range (0.1–0.2 g mL−1), although no clear inhibition zone was observed for S. sclerotiorum. Furthermore, the WP maintained 65% viability after 24 months of storage at 4 °C. These results demonstrate the potential of FD microencapsulation to enhance the storage stability of Bacillus subtilis formulations while preserving their antifungal activity.