Bacillus velezensis 7-A as a Biocontrol Agent Against Fusarium verticillioides, the Causal Agent of Rice Sheath Rot Disease

Rice sheath rot has progressively developed into a growing threat to global rice production, particularly in intensively managed systems conducive to disease development. Therefore, accurate identification of the causal pathogen and the development of sustainable management strategies represent urgent scientific requirements. In this study, we isolated the causal organism of rice sheath rot from infected rice tissues and identified it as <i>Fusarium verticillioides</i> based on multi-locus sequence analysis. Eight endophytic bacterial strains were recovered from healthy rice root systems. Among the isolates, <i>Bacillus velezensis</i> isolate 7-A exhibited the strongest antifungal activity against <i>F. verticillioides</i>. This isolate demonstrated broad-spectrum antifungal activity, with inhibition rates ranging from 54.8% to 71.8%. Phylogenetic analysis based on 16S rRNA and <i>gyrB</i> gene sequences identified it as <i>B. velezensis</i>. Further characterization revealed that <i>B. velezensis</i> 7-A is capable of secreting proteases and synthesizing siderophores. The filtered liquid from sterile fermentation markedly inhibited the growth of mycelium in <i>F. verticillioides</i> and induced marked morphological abnormalities. Liquid LC-MS analysis identified multiple antifungal active substances, including camphor, ginkgolides B, salicin, cinnamic acid, hydroxygenkwanin, stearamide, <i>β</i>-carotene, and others. A pot experiment demonstrated that the fermentation broth of <i>B. velezensis</i> 7-A effectively suppressed the occurrence of rice sheath rot, achieving a relative control efficacy of 61.3%, which is comparable to that of a 10% carbendazim water-dispersible granule (WDG). Additionally, isolate 7-A enhances plant disease resistance by activating the activities of key defense enzymes. These findings provide preliminary insights into its potential application in integrated and sustainable disease management programs.