Enhancing cucumber growth and disease resistance against Sclerotinia sclerotiorum by exogenous co-inoculation of Bacillus amyloliquefaciens KACC17029 and Salicylic acid

Cucumber ( Cucumis sativus L.) is a widely cultivated crop worldwide but is highly vulnerable to Sclerotinia sclerotiorum , a destructive fungal pathogen that affect both yield and quality. This study evaluates the synergistic effects of Bacillus amyloliquefaciens KACC17029 and salicylic acid (SA) in promoting cucumber growth, enhancing internal defense mechanisms, and modulating rhizosphere microbial communities under pathogen stress. Co-application of B. amyloliquefaciens and SA restricted fungal mycelial growth by 24.31% in vitro, while significantly improving phenotypic traits such as leaf area (101.26 cm²) and fresh weight (38.2 g) and reducing lesion size by 83.79% in greenhouse conditions. Activities of key defense-related enzymes, including polyphenol oxidase and peroxidase, were elevated up to 4.3-fold and 6-fold, respectively. Expression of defense-related genes (PR1, LecRK6.1) was significantly upregulated. Microbiome profiling revealed increased abundance of beneficial taxa such as Trichoderma , Noviherbaspirillum , and Candida , alongside suppression of the pathogenic fungus Fusarium . These findings demonstrate that the co-inoculation strategy significantly boosts cucumber health and growth by activating internal plant defense and shaping the rhizosphere. This eco-friendly, biologically based approach offer sustainable alternative to crop protection and integrated disease management.