3-Methylpentanoic Acid Controls Wheat Blast Disease by Disrupting Cell Wall Integrity and Putatively Targeting UDP-Glucose 4-Epimerase.

Wheat blast, caused by Magnaporthe oryzae Triticum (MoT), is a devastating fungal disease threatening global food security. Emergence of fungicide-resistant MoT populations necessitates safe, eco-friendly alternatives. This study evaluates the biorational potential of 3-methylpentanoic acid (3-MP), a volatile organic compound (VOC) produced by Bacillus safensis NI2B against MoT. In vitro assays demonstrated that 3-MP inhibits MoT mycelial growth, conidiogenesis, conidial germination, and appressorium formation in a dose-dependent manner, achieving complete suppression at 100-125 µM. Furthermore, detached leaf, seedling, and spike assays revealed robust preventive and curative efficacy, indicating strong translational potential for wheat blast management. Mechanistic analyses indicated reduced fungal cellular viability following 3-MP treatment, as confirmed by fluorescein diacetate staining. In silico molecular docking and dynamics simulations predicted that 3-MP putatively interacts with UDP-glucose 4-epimerase (UGE), a key enzyme in galactose metabolism and cell wall integrity. 3-MP binds stably within the NAD+-associated Rossmann fold of UGE, sterically hindering substrate access and perturbing NAD+ orientation. RT-qPCR expression analysis was consistent with this model, showing a biphasic response characterized by early induction followed by significant repression of UGE transcripts, which aligns with disrupted UDP-glucose metabolism and impaired cell wall biosynthesis. Collectively, this study establishes 3-MP as a potent biocontrol agent and provides preliminary mechanistic insights into its antifungal activity associated with UGE perturbation. These findings offer a promising molecular framework for developing VOC-based integrated pest management strategies against wheat blast.