Biocontrol Mechanism of Bacillus thuringiensis GBAC46 Against Diseases and Pests Caused by Fusarium verticillioides and Spodoptera frugiperda

<i>Bacillus thuringiensis</i> (<i>Bt</i>) is widely recognized as the most important microbial pesticide controlling various insect pests and diseases due to its insecticidal crystal proteins (ICPs) and antimicrobial metabolites. The current study investigates the biocontrol potential of <i>B. thuringiensis</i> GBAC46 against the fungal pathogen <i>Fusarium verticillioides</i> and the insect pest <i>Spodoptera frugiperda</i> through multiple mechanisms. Phenotypic experiments revealed that GBAC46 effectively inhibited <i>F. verticillioides</i> growth by inducing reactive oxygen species (ROS) accumulation and showed enhanced larvicidal activity against second instar <i>S. frugiperda</i> larvae. Pot experiments showed that feeding by <i>S. frugiperda</i> enhanced <i>F. verticillioides</i> infection in maize. The <i>Bt</i> strain GBAC46 effectively controlled both pests and diseases in greenhouse maize seedlings. Applying the <i>Bt</i> strain GBAC46 reduced feeding damage from <i>S. frugiperda</i>, decreased leaf yellowing and wilting caused by <i>F. verticillioides</i>, and improved growth indicators such as plant height, fresh weight, and dry weight. RT-qPCR results revealed that the <i>Bt</i> strain GBAC46 induced key defense genes in maize involved in activating salicylic acid, jasmonic acid, and ethylene pathways. The overall study demonstrated and confirmed the GBAC46 strain as a promising microbial agent for disease and pest management.