Combining Bacillus and Trichoderma in Bio-Organic Fertilizers with Reduced Chemical Fertilizer: An Effective Strategy Against Cucumber Fusarium Wilt

Integrated fertilization using reduced chemical fertilizers and bio-organic fertilizers can maintain soil fertility with lower chemical inputs, yet its systemic effects on disease control, soil microbes, yield, and quality are not fully clear. This study aimed to: (1) evaluate the effects of <i>Bacillus amyloliquefaciens</i> Z2 and <i>Trichoderma harzianum</i> T22, alone or combined, on suppressing <i>Fusarium</i> wilt (<i>Fusarium oxysporum</i> f. sp. <i>cucumerinum</i>) and promoting cucumber growth in pot experiments; and (2) assess the field efficacy of reduced chemical fertilizer (75% N) plus microbial bio-organic fertilizer (25% N) for disease control, growth enhancement, and yield and quality improvement. To achieve these objectives, pot experiments were first conducted, followed by field experiments. Pot results indicated that individual and combined inoculants notably decreased the disease index (DI) by 40.48-68.75%, and significantly increased cucumber fresh shoot biomass by 16.86-26.75%, with the combined inoculants exhibiting the greatest effect. Field experiments indicated that the synthetic microbial bio-fertilizer has a greater advantage in promoting cucumber growth and disease suppression compared to a single bacterial bio-organic fertilizer. Specifically, the application of combined bio-fertilizers exhibited the best performance in decreasing cucumber DI by 51.54%, improving cucumber fresh shoot biomass by 12.19%, and enhancing cucumber yield by 21.02%, along with significantly improving fruit vitamin C content by 21.17% and increasing fruit total amino acids by 26.23% compared with the control. Rhizosphere soil analysis revealed that the application of combined bio-fertilizers enriched beneficial bacterial families (JG30-KF-AS9 and <i>Sphingomonadaceae</i>) and fungal genera (<i>Chaetomiaceae</i> and <i>Condenascus</i>) with known biocontrol functions and suppressed the proliferation of <i>Fusarium</i>. Overall, the integrated use of reduced chemical fertilizer combined with synthetic bio-organic fertilizer effectively suppresses cucumber wilt, optimizes microbial community structure, and improves cucumber yield and quality, furnishing a valuable foundation for microbial-assisted sustainable crop production.