Kemmerer, L. E. | bioRxiv Science

bioRxiv2026

Soil-derived Bacillus pumilus strains demonstrate antagonistic activity against Magnaporthe oryzae and multiple plant growth-promoting traits

Biological control strategies are increasingly being explored as sustainable alternatives for managing rice blast disease caused by Magnaporthe oryzae. In this study, we characterized three Bacillus pumilus isolates (DC01, DC09, and DC13) and evaluated their antifungal and plant-beneficial properties against M. oryzae. Whole genome sequencing revealed multiple biosynthetic gene clusters associated with the production of antimicrobial metabolites. All three isolates inhibited fungal growth in dual-culture assays, whereas heat-stable diffusible antifungal activity was primarily associated with the cell-free supernatants of DC09 and DC13. Exposure to bacterial supernatants disrupted fungal development, inducing abnormal hyphal morphology characterized by bulbous swelling, altered polarity, and increased branching in M. oryzae. Volatile organic compound assays further revealed that the DC isolates suppress fungal growth in the absence of physical contact. The isolates additionally inhibited the growth of other phytopathogenic fungi and selected human bacterial pathogens. All strains exhibited plant growth-promoting traits, including indole-3-acetic acid production and osmotic stress tolerance, whereas DC09 also displayed phosphate-solubilizing activity. Importantly, root inoculation with the DC isolates significantly reduced rice blast disease severity and induced expression of defense-associated genes involved in jasmonic acid/ethylene signaling and immune priming. Collectively, these findings identify the DC isolates, particularly DC09 and DC13, as promising multi-mechanistic biological control agents for sustainable rice blast management.

microbiology↗

bioRxiv2025

Bacillus subtilis strain UD1022 as a biocontrol agent against Magnaporthe oryzae, the rice blast pathogen

Rice blast disease, caused by Magnaporthe oryzae, is a major threat to global rice production, necessitating sustainable disease management strategies. Compared to chemical pesticides, biocontrol agents, such as beneficial microbe antagonists, offer a sustainable approach to naturally inhibit plant pathogens. This study evaluates the biocontrol potential of Bacillus subtilis UD1022 against M. oryzae through both direct antagonism and volatile-mediated inhibition. In dual culture assays, UD1022 significantly inhibited fungal growth. Furthermore, a stacking plate assay demonstrated that UD1022 produces volatile organic compounds (VOCs) that suppress fungal growth. Beyond vegetative growth inhibition, UD1022 also disrupted key infection processes of M. oryzae. Spore germination was reduced by 50%, while appressorium formation decreased by approximately 44% in UD1022-treated samples. In planta assays revealed that UD1022-treated rice plants exhibited a substantial reduction in disease severity compared to untreated controls. This reduction correlated with the upregulation of key defense genes in the salicylic acid, jasmonic acid, and ethylene signaling pathways, suggesting that UD1022 primes systemic resistance in rice plants. These findings establish UD1022 as a potent biocontrol agent capable of suppressing M. oryzae through direct antagonism, VOC-mediated inhibition, and induction of systemic resistance. This study underscores the potential of UD1022 as an eco-friendly alternative to chemical fungicides for managing rice blast disease. IMPORTANCEMagnaporthe oryzae is a destructive fungal pathogen that causes rice blast disease, leading to significant yield losses and threatening global food security. Here, we investigated the biocontrol potential of Bacillus subtilis UD1022, a beneficial rhizobacterium known for its plant growth-promoting and antifungal properties. Our in vitro and in planta studies revealed that UD1022 suppresses M. oryzae through direct antagonism, volatile organic compound (VOC)-mediated inhibition, and the induction of systemic resistance in rice. These findings demonstrate UD1022 as a promising candidate for microbial-based disease management and the role of beneficial bacteria in enhancing crop protection. This research contributes to the development of sustainable agricultural practices by leveraging naturally occurring microbes to improve plant resilience and disease resistance.

microbiology↗