Cucumber is an important economic crop widely cultivated globally. Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum , seriously affects its yield and quality and is difficult to control. Here, we isolated a novel Bacillus velezensisstrain (LJ-19) from cucumber rhizosphere. Through assays for antibacterial activity, enzymatic activity, detection of disease resistance genes, and plant growth-promoting activity, this strain exhibited pronounced antagonistic activity against Fusarium oxysporum f. sp. cucumerinum and possessed plant growth-promoting traits. Notably, the inhibition of Fusarium oxysporum f. sp. cucumerinum mycelial growth and spore germination by LJ-19 was primarily contact-dependent, rather than mediated by diffusible antibiotics. Meanwhile, LJ-19 enhanced the activities of key defense enzymes—superoxide dismutase (SOD), peroxidase (POD), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO), thereby contributing to plant protection, and the transcript levels of defense-related genes, including Nonexpressor of pathogenesis-related genes 1 (NPR1), Pathogenesis -related gene 3 (PR3), Lipoxygenase 1 (LOX1), Constitutive triple response 1 (CTR1), and Phenylalanine ammonia-lyase 1 (PAL1), were up-regulated. Pot experiments demonstrated that LJ-19 treatment significant increased the stem thickness, fresh weight, leaf area, and overall biomass in cucumber. LJ-19 was also been confirmed could thrive in nitrogen-free environment and solubilize inorganic phosphorus, produce indole-3-acetic acid (IAA) and siderophores. Collectively, these findings demonstrate that Bacillus velezensis LJ-19 suppresses cucumber Fusarium wilt via direct antagonism and induction of systemic resistance. They also provide insights into the molecular mechanisms by which LJ-19 controls Fusarium Wilt and promotes cucumber growth, highlighting its potential as an effective biocontrol agent for sustainable cucumber.
Li et al. (Thu,) studied this question.
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