Lasiodiplodia theobromae is a major postharvest pathogen causing nutmeg black rot and was identified as the
causal agent in Thailand, representing the first report in the country. Among 25 rhizosphere bacterial isolates,
Priestia aryabhattai C-KT-3 exhibited the strongest antifungal activity in vitro, significantly reducing fungal
growth in a concentration-dependent manner. In vivo assays showed that both culture filtrates and bacterial cells
reduced disease severity without adversely affecting fruit quality. These results demonstrate that C-KT-3 exhibits
significant antifungal activity under both in vitro and fruit conditions. Genome analysis revealed multiple
biosynthetic gene clusters, suggesting metabolic potential, while LC–QTOF–MS profiling indicated a chemically
diverse set of putative metabolites. Biochemical assays suggested the induction of oxidative stress responses in
the pathogen following treatment. Overall, these findings indicate that multiple mechanisms may contribute to
the observed antifungal activity and highlight C-KT-3 as a promising biocontrol agent for postharvest nutmeg
disease management.