TiO₂-Ni Hybrid Suspension as Visible-Light-Responsive Antifungal Agents for Controlling Phytophthora palmivora

Black pod disease caused by Phytophthora palmivora (P. palmivora) remains a major constraint in global cocoa production, leading to yie ld losses of up to 40 % and increased resistance to synthetic fungicides. In this study, a novel visible-light-responsive TiO₂-Ni hybrid suspension system was synthesized via a modified sol-gel method and evaluated as an eco-friendly antifungal agent specifically against P. palmivora. Structural, morphological, and compositional analyses using FTIR, XRD, and SEM-EDX confirmed the successful incorporation of Ni into the TiO₂ lattice, while UV-Vis DRS revealed a red shift in absorption and a narrowed band gap from 3.20 eV to 3.05 eV. Antifungal performance was assessed in vitro at various concentrations (0.1-1.0 % w/v) under dark, UV, and visible-light conditions. The TiO₂-Ni suspension exhibited the highest inhibition under visible-light irradiation, achieving near-complete inhibition of mycelial growth at 0.5-1.0 % concentrations, whereas minimal activity was observed under dark conditions. This enhanced performance is attributed to improved electron-hole separation and increased generation of reactive oxygen species (ROS), leading to membrane disruption and cell damage. These findings highlight the TiO₂-Ni hybrid suspension as a promising and sustainable alternative to conventional fungicides for controlling P. palmivora in cocoa cultivation.