Abstract: To enrich the biocontrol bacterial resources against peanut southern blight (caused by Sclerotium rolfsii), this study isolated a strain YJ02 with strong antagonistic activity against S.rolfsii from diseased peanut pods collected in Yanjin, Henan, using dilution plating and plate confrontation assays. Through morphological, physiological, biochemical, and molecular analyses (16S rRNA and gyrB gene sequencing), strain YJ02 was identified as Bacillus velezensis. The inhibitory mechanism of B.velezensis YJ02 against S.rolfsii was investigated via dual-culture assays and cell-free fermentation filtrate tests. Additionally, pot experiments were conducted to evaluate its disease control efficacy and growth-promoting effects. Results showed that strain YJ02 exhibited an inhibition rate of 83.25% against S.rolfsii in plate assays, causing hyphal deformities and inhibiting sclerotia formation. Treatment with its sterile fermentation filtrate significantly reduced the secretion of pathogenic enzymes (oxalic acid, cellulase, and pectinase) per unit biomass of S.rolfsii. In pot trials, strain YJ02 achieved a disease control efficacy of 63.45% against peanut southern blight and notably promoted plant growth, including increases in plant height, fresh weight, root length, and root weight. In conclusion, B.velezensis YJ02 demonstrates promising potential for the biocontrol of peanut southern blight.

Key words: peanut southern blight, Sclerotium rolfsii, Bacillus velezensis YJ02, biological control