FUNGI vs. ROOT KNOT NEMATODES: MECHANISMS OF BIOCONTROL
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Root-knot nematodes (Meloidogyne spp.) are among the most damaging plant-parasitic nematodes, causing significant yield losses across major crops. These endoparasites weaken plants by disrupting root systems and often exacerbate damage when interacting with viruses, sometimes leading to synergistic effects that intensify plant stress. Chemical nematicides, though effective, pose environmental and health risks. Biocontrol offers a sustainable alternative, providing environmentally friendly means to suppress nematodes while maintaining soil health. Bhat et al. (2023) reviews fungal nematode biocontrol mechanisms extensively:
Toxin-Producing Fungi
Control root-knot nematodes by secreting mycotoxins that cause paralysis and death. P. ostreatus, produce nematotoxic compounds like trans-2-decenoic acid, which disrupt nematode movement upon contact, leading to rapid recoiling and eventual inactivation. Prolonged exposure allows fungal hyphae to penetrate the nematode body, often through the mouth, digesting internal tissues within days.
Endoparasitic fungi
Act as biocontrol agents by infecting nematodes through their conidia and developing internally. These fungi lack a significant saprophytic phase and rely on direct parasitism. D. coniospora produces metabolites with strong nematicidal activity. One key compound was found responsible: 5-hydroxymethylfuran-2-carboxylic acid that caused 100% juvenile mortality and reduced egg hatch rates.
Ovicidal fungi
Act as biocontrol agents against root-knot nematodes by directly targeting and destroying eggs, cysts, and females. Their mode of action involves parasitism of egg masses and enzymatic breakdown of egg structures, leading to inhibited hatching and increased juvenile mortality. Applications of effective isolates like Purpureocillium lilacinum in soil or with organic amendments significantly reduce gall formation and nematode populations.
Nematode-trapping Fungi
Nematode-trapping fungi suppress root-knot nematodes through specialized physical structures such as constricting rings, adhesive knobs, and networks that capture and immobilize juveniles. Once trapped, the fungi penetrate the nematode cuticle and digest internal contents for nutrient assimilation. The formation of traps is often induced by nematode presence and increases over time. Some species, like Arthrobotrys oligospora and Dactylaria brochopaga, also produce enzymes that break down nematode tissues, enhancing lethality.
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Source: https://www.mdpi.com/2223-7747/12/3/451
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