β-Aminobutyric acid enhances <i>Arabidopsis thaliana</i> resistance to the hemibiotrophic fungal pathogen <i>Colletotrichum higginsianum</i>

β-Aminobutyric acid (BABA) is a nonproteinogenic amino acid that functions as a potent plant defense activator, conferring broad-spectrum resistance in many plants. Although its effects on biotrophic and necrotrophic pathogens are well known, the molecular basis of BABA-induced resistance (BABA-IR) against the hemibiotrophic fungus Colletotrichum higginsianum remains unclear. In this study, we investigated BABA’s effects on C. higginsianum-infected Arabidopsis thaliana. Foliar BABA application (1.25-10 mM) reduced lesion size and fungal biomass in a concentration-dependent manner, with 5-10 mM being most effective. Microscopy showed that BABA treatment prevented fungal invasion beyond the appressorium stage. Mutant analysis revealed that BABA-IR depends on salicylic acid (SA) biosynthesis (NahG and eds16-1) and the signaling components EDS1 and NDR1. In contrast, mutants insensitive to jasmonic acid and ethylene (jar1-1 and ein2-12, respectively) retained BABA-mediated protection. These findings indicate that BABA primes SA-dependent defenses against C. higginsianum while highlighting its potential for improving sustainable crop protection.