Sustainable control of Phytophthora capsici in bell pepper using encapsulated Limosilactobacillus fermentum and reduced fungicide doses

Phytophthora capsici causes severe losses in pepper cultivation, and sustainable biocontrol strategies are needed to reduce reliance on chemical fungicides. This study reports the isolation and functional evaluation of a lactic acid bacterium (Limosilactobacillus fermentum GS-15) from traditional yogurt, with proven antagonistic activity against P. capsici. The strain was identified via 16 S rRNA sequencing and assessed through in vitro assays, including dual culture and volatile organic compound (VOC) production. GS-15 inhibited P. capsici mycelial growth by 50.0%, while VOCs produced by GS-15 reduced growth by 38.9%. Exogenous lactic acid at a 90% concentration inhibited fungal growth by 88.9%, indicating the sensitivity of the pathogen to lactic acid. To enhance bacterial stability in the presence of chemical fungicide Previcur Energy®, the GS-15 was encapsulated in calcium–alginate beads. This encapsulation preserved viability and enhanced antagonistic activity to 61% inhibition. Greenhouse experiments using three bell pepper cultivars showed that GS-15 application significantly reduced disease incidence compared to untreated or fungicide-only treatments. The combination of GS-15 and a half-dose of fungicide reduced disease incidence to ≤ 10%, surpassing the performance of full-dose fungicide. Alginate-encapsulated GS-15 alone or with half-dose fungicide resulted in complete disease suppression in all cultivars tested. These results demonstrate that GS-15, especially when encapsulated, is an effective biocontrol agent. Its positive action with reduced fungicide inputs provides a promising tool for integrated pest management in sustainable pepper production. To the best of our knowledge, this study shows, for the first time, the potential of a human probiotic for controlling phytopathogenic P. capsici.