Rhizosphere Bacterial Community Shifts in Rice Blast–Resistant Cultivars and the Antagonistic Activity of Bacillus velezensis

The rhizosphere microbiome is associated with plant health and may contribute to interactions between rice and the rice blast pathogen, Magnaporthe oryzae. In this greenhouse study, 16 S rDNA amplicon sequencing was used to compare rhizobacterial communities associated with blast-resistant and blast-susceptible rice cultivars before and after pathogen infection. Significant differences in rhizobacterial diversity and community composition were observed between resistant and susceptible cultivars, with distinct community shifts following pathogen challenge. Differential microbial enrichment patterns were detected across cultivars and disease conditions. Notably, Bacillus spp. were consistently enriched in healthy plants of resistant cultivars and in infected plants of susceptible cultivars, indicating their association with disease status and potential ecological roles in the rice rhizosphere. Network analysis further showed that cultivar resistance was associated with differences in rhizosphere microbial community structure. Additionally, a bacterial strain, Bacillus velezensis H2, was isolated from the same rhizosphere of healthy rice plants and characterized using morphological, biochemical, and genomic analyses, including 16 S rRNA sequencing and SNP profiling. Whole-genome analysis using antiSMASH identified multiple biosynthetic gene clusters involved in secondary metabolite production, including nonribosomal peptide synthetases. In addition, B. velezensis H2 exhibited strong in vitro antifungal activity against M. oryzae, supporting its potential as a biocontrol candidate. Overall, this study describes rhizosphere bacterial community shifts associated with rice blast resistance and identifies B. velezensis H2 as a promising antagonistic bacterium for the sustainable management of rice blast disease.