The Biocontrol Effect and Induced Disease Resistance Mechanism of Bacillus velezensis FJ17-4 on Cucumber Fusarium Wilt

Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum Owen (FOC) is a major disease affecting cucumber production. Developing environmentally friendly prevention and control strategies is essential for managing cucumber Fusarium wilt (CFW). Bacillus velezensis is a beneficial microorganism with biocontrol potential against plant diseases. To investigate the biocontrol efficacy and induced disease resistance mechanism of B. velezensis FJ17-4 against CFW, the biocontrol effect of FJ17-4 on CFW was determined through indoor pot cultivation experiments, and the transcriptome of cucumber root samples treated with FJ17-4 was sequenced and analyzed by RNA-Seq technology. The results showed that CFW incidence was significantly reduced after FJ17-4 treatment, with 68.75% control efficacy, higher than that of Kasugamycin. A total of 1041 differentially expressed genes (DEGs) were induced, including 477 upregulated and 564 downregulated genes. DEGs associated with plant–pathogen interaction pathways (such as carbon metabolism, phenylpropanoid biosynthesis and amino acid biosynthesis), calcium (Ca2+) signaling pathway, and plant hormone signaling pathways [such as salicylic acid (SA), ethylene (ET), and jasmonic acid (JA)] were induced. These responses activated the disease resistance system of cucumber against CFW. Quantitative RT-PCR validation of 10 annotated DEGs confirmed consistent expression trends with the transcriptomic data. The results indicate that FJ17-4-induced disease resistance involves multiple genes and coordinated regulation of metabolisms, with hormone-mediated defense signaling pathways playing important roles. The transcriptome sequencing data provides a scientific basis for exploring the induced disease resistance mechanism of FJ17-4 and developing environmentally friendly biocontrol strategies.