Biocontrol Efficacy of Brevibacillus agri DR2-1 Against Meloidogyne incognita in Cucumber Through Dual Mechanisms: Direct Nematicidal Activity and Induced Resistance

Root-knot nematodes (RKNs, Meloidogyne spp.) are a major threat to global crop production. The search for effective and environmentally friendly biocontrol strategies is urgently needed. Brevibacillus species have shown broad biocontrol potential, but the application of Brevibacillus agri for nematode management has not been reported. This study identified a novel Br. agri strain, DR2-1, as a promising biocontrol agent against M. incognita in cucumber. This is the first report demonstrating the nematicidal potential of Br. agri . DR2-1 fermentation supernatant exhibited direct nematicidal activity against second-stage juveniles and eggs. In greenhouse and field trials, DR2-1 application significantly suppressed nematode infection and promoted plant growth. The split-root test and transcriptomic analysis suggested that DR2-1 pretreatment enhances plant defense responses, and application of DR2-1 triggers the expression of genes related to phenylpropanoid biosynthesis, MAPK signaling, calcium signaling, and monooxygenase activity pathways. The efficacy of the strain DR2-1 supports its potential as a biocontrol agent against RKNs.