Bacillus Bsu02 and Bha48 increase wax gourd resistance to Fusarium proliferatum via multiple mechanisms

• Bsu02 and Bha48 effectively inhibited mycelial growth of Fusarium graminearum . • Bsu02 and Bha48 could induce systemic resistance of wax gourd plant. • Bsu02 and Bha48 promoted the growth of wax gourd plant. • Bsu02 and Bha48 remodeled wax gourd rhizosphere community structure. Wax gourd ( Benincasa hispida ) wilt has caused significant economic losses. In this study, a pathogen causing wax gourd wilt was isolated from diseased wax gourd plant and identified as Fusarium proliferatum based on morphological characteristics and molecular analysis. In order to control the disease, 62 Bacillus strains were isolated from rhizosphere soil of 6 plant species, with inhibition efficiency ranging from 21.81 % to 81.40 % at 6 days in the dual culture test. And the strains Bsu02 and Bha48 were selected for further investigation. The volatile organic compounds (VOCs) of Bsu02 and Bha48 inhibited mycelial growth of F. proliferatum with inhibition efficiency of 55.61 % and 38.05 % at 7 days, respectively. Pretreatment with either individual Bacillus strains (Bsu02 or Bha48) or their combination (Bcom) reduced wilt disease index of wax gourd seedlings, with control efficacy of 47.51 %, 44.57 %, and 37.04 %, respectively. Additionally, pretreatments with Bsu02, Bha48, and Bcom increased the activities of peroxidase (POD), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) by more than 0.40-fold in wax gourd plant. These Bacillus pretreatments also upregulated the expression of pathogenesis-related (PR) genes ( PR5 , PR6 , and PR12 ). Furthermore, Bacillus application significantly improved plant growth parameters, including plant height, leaf area, shoot fresh weight, and root dry weight, as well as photosynthetic parameters. Moreover, Bsu02, Bha48, and Bcom changed community compositions of rhizosphere microorganisms and increased alpha diversity of bacterial and fungal communities. In summary, Bsu02, Bha48, and Bcom increased wax gourd seedling resistance to wax gourd wilt caused by F. proliferatum via multiple mechanisms.