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<p>Global food security is increasingly threatened by plant diseases and the excessive use of chemical pesticides and fertilizers, highlighting the urgent need for sustainable and environmentally friendly alternatives. Nanotechnology and biological agents such as plant-growth-promoting rhizobacteria (PGPR), particularly <i>Bacillus</i> spp., offer cutting-edge strategies for sustainable crop protection. This study investigates the individual and synergistic effects of <i>Bacillus</i> culture filtrate (BCF) and zinc oxide nanoparticles (ZnO-NPs) in controlling <i>Pantoea</i> sp., the causal agent of bacterial leaf spot (BLS) in cucumber, and enhancing plant performance under greenhouse conditions. Antimicrobial activity was assessed in vitro, <i>Bacillus</i>-derived secondary metabolites were identified via gas chromatography–mass spectrometry (GC–MS), and plant health indicators—including disease severity, physiological traits, and fruit yield—were evaluated under greenhouse conditions. The in vitro assays revealed that ZnO-NPs exhibited a concentration-dependent antibacterial effect, with inhibition zones increasing from 3&#xa0;mm at 0&#xa0;ppm to 38&#xa0;mm at 200&#xa0;ppm. Meanwhile, <i>Bacillus</i> culture filtrate alone produced a significant inhibition zone of 40&#xa0;mm against <i>Pantoea</i> sp. GC–MS analysis of the methanolic extract of <i>Bacillus</i> sp. identified twenty bioactive compounds, many of which are known for their antimicrobial and plant growth-promoting properties, likely contributing to the observed effects. Under greenhouse conditions challenged with <i>Pantoea</i> sp., the co-application of 200&#xa0;ppm ZnO-NPs and <i>Bacillus</i> culture filtrate significantly reduced bacterial leaf spot severity in cucumber plants, lowering the symptom score to 1.1 on a 1–7 scale. This combined treatment also significantly enhanced physiological traits, including leaf chlorophyll content (SPAD value: 59.0), total phenolic content (1.76&#xa0;mg GAE g<sup>−1</sup> FW), and leaf macro- and micronutrient levels, while maximizing productivity—achieving the highest fruit number per plant (14.2) and total yield (2.42&#xa0;kg/plant). These findings support the integration of ZnO-NPs and <i>Bacillus</i>-based biostimulants as a promising eco-friendly strategy for disease management and productivity enhancement in cucumber cultivation.</p> Graphical abstract <p></p>

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Synergistic protective effects of rhizobacterial culture filtrate and zinc oxide nanoparticles against Pantoea leaf spot in cucumber

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月29日

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  • Amira A. Helaly,
  • Amany H. M. Shams,
  • Ibrahim A. A. Mohamed,
  • Eman F. A. Awad-Allah

摘要

Global food security is increasingly threatened by plant diseases and the excessive use of chemical pesticides and fertilizers, highlighting the urgent need for sustainable and environmentally friendly alternatives. Nanotechnology and biological agents such as plant-growth-promoting rhizobacteria (PGPR), particularly Bacillus spp., offer cutting-edge strategies for sustainable crop protection. This study investigates the individual and synergistic effects of Bacillus culture filtrate (BCF) and zinc oxide nanoparticles (ZnO-NPs) in controlling Pantoea sp., the causal agent of bacterial leaf spot (BLS) in cucumber, and enhancing plant performance under greenhouse conditions. Antimicrobial activity was assessed in vitro, Bacillus-derived secondary metabolites were identified via gas chromatography–mass spectrometry (GC–MS), and plant health indicators—including disease severity, physiological traits, and fruit yield—were evaluated under greenhouse conditions. The in vitro assays revealed that ZnO-NPs exhibited a concentration-dependent antibacterial effect, with inhibition zones increasing from 3 mm at 0 ppm to 38 mm at 200 ppm. Meanwhile, Bacillus culture filtrate alone produced a significant inhibition zone of 40 mm against Pantoea sp. GC–MS analysis of the methanolic extract of Bacillus sp. identified twenty bioactive compounds, many of which are known for their antimicrobial and plant growth-promoting properties, likely contributing to the observed effects. Under greenhouse conditions challenged with Pantoea sp., the co-application of 200 ppm ZnO-NPs and Bacillus culture filtrate significantly reduced bacterial leaf spot severity in cucumber plants, lowering the symptom score to 1.1 on a 1–7 scale. This combined treatment also significantly enhanced physiological traits, including leaf chlorophyll content (SPAD value: 59.0), total phenolic content (1.76 mg GAE g−1 FW), and leaf macro- and micronutrient levels, while maximizing productivity—achieving the highest fruit number per plant (14.2) and total yield (2.42 kg/plant). These findings support the integration of ZnO-NPs and Bacillus-based biostimulants as a promising eco-friendly strategy for disease management and productivity enhancement in cucumber cultivation.

Graphical abstract