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<p>Damping-off caused by <i>Pythium aphanidermatum</i> is a destructive disease of tomato, leading to substantial seedling losses in nurseries. This study was performed to investigate the ability of 107 ectorhizosphere and 68 rhizoplane bacterial isolates, compared with 12 commercial strains, to promote plant growth and control this pathogen. Initial screening was based on growth promotion via seed treatment. Biological control was then investigated through direct confrontation and induction of systemic resistance using a split-root system. Disease severity was assessed using a 5-point scale and converted to continuous values based on the mid-point of each severity interval for statistical analysis. In biocontrol tests, five rhizobacteria—three native (E8, E18, B124) and two commercial (<i>Bacillus pumilus</i> INR7 and <i>Bacillus</i> sp.)—achieved disease reduction rates of 85.8%, 85.8%, 56.8%, 75.5%, and 28.4%, respectively, with the split-root assay confirming the role of induced systemic resistance. Molecular identification of the three native biocontrol isolates via 16&#xa0;S rRNA sequencing revealed that E8, E18, and B124 exhibited the highest similarity to <i>B. cereus</i>, <i>B. licheniformis</i>, and <i>Achromobacter</i> sp., respectively. The results revealed that these indigenous rhizoplane-colonizing strains, particularly when formulated with protective carriers like kaolin, represent promising biocontrol agents for sustainable management of tomato damping-off.</p>

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Screening of bacterial isolates from the rhizosphere and rhizoplane of tomato roots and their comparison with commercial isolates in the control of damping-off caused by Pythium aphanidermatum

  • 期刊论文

  • 发表日期：

    2026年5月25日

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  • Mohsen Amanimehr,
  • Mahyar Sheikholeslami

摘要

Damping-off caused by Pythium aphanidermatum is a destructive disease of tomato, leading to substantial seedling losses in nurseries. This study was performed to investigate the ability of 107 ectorhizosphere and 68 rhizoplane bacterial isolates, compared with 12 commercial strains, to promote plant growth and control this pathogen. Initial screening was based on growth promotion via seed treatment. Biological control was then investigated through direct confrontation and induction of systemic resistance using a split-root system. Disease severity was assessed using a 5-point scale and converted to continuous values based on the mid-point of each severity interval for statistical analysis. In biocontrol tests, five rhizobacteria—three native (E8, E18, B124) and two commercial (Bacillus pumilus INR7 and Bacillus sp.)—achieved disease reduction rates of 85.8%, 85.8%, 56.8%, 75.5%, and 28.4%, respectively, with the split-root assay confirming the role of induced systemic resistance. Molecular identification of the three native biocontrol isolates via 16 S rRNA sequencing revealed that E8, E18, and B124 exhibited the highest similarity to B. cereus, B. licheniformis, and Achromobacter sp., respectively. The results revealed that these indigenous rhizoplane-colonizing strains, particularly when formulated with protective carriers like kaolin, represent promising biocontrol agents for sustainable management of tomato damping-off.