Bacillus velezensis Enhances Rice Resistance to Brown Spot by Integrating Antifungal and Growth Promotion Functions

Brown spot, caused by the seedborne fungus <i>Bipolaris oryzae</i>, remains a major constraint in rice production. Here, we used in vitro and in vivo assays to evaluate the biocontrol potential of three <i>Bacillus</i> strains (<i>Ba. cereus</i> OQ725688.1, <i>Ba. velezensis</i> OP938696.1, and <i>Ba. subtilis</i> OP937353.1) against <i>Bi. oryzae</i> in two rice cultivars ("Rubelita" and "Predileta"). <i>Ba. cereus</i> showed the highest in vitro mycelial inhibition (≈95%), whereas <i>Ba. velezensis</i> was the most effective under greenhouse conditions, reducing disease severity by up to 60% and increasing seedling vigor by 51% compared with infected controls. "Predileta" showed the strongest response to bacterial treatment, maintaining severity scores below 2 even under high inoculum pressure. Functional assays confirmed that all strains displayed amylolytic, catalase, and phosphate-solubilizing activities, with <i>Ba. velezensis</i> uniquely expressing strong cellulase and protease activities. Genome analysis of <i>Ba. velezensis</i> OP938696.1 revealed multiple biosynthetic gene clusters for antifungal polyketides and lipopeptides. These integrated biochemical and genomic traits demonstrate the novelty and potential of this Neotropical strain as a multifunctional agent capable of suppressing <i>Bi. oryzae</i> while enhancing rice seedling performance. Incorporating such a native strain into seed and soil management offers a sustainable strategy for rice protection in Neotropical systems.