Pochonia chlamydosporia for nematode control

1. What is Pochonia chlamydosporia?

It is a soil-borne, filamentous fungus (Ascomycete) that is an obligate parasite of nematode eggs and females. It was previously classified as Verticillium chlamydosporium. It is found naturally in soils worldwide and is considered a fungal endophyte (can live within plant roots without causing disease).

2. Mode of Action: How It Controls Nematodes

Its control is multi-faceted and highly specialized:

• Primary Action: Parasitism of Eggs and Females

  • The fungus recognizes chemical signals from nematode eggs.

  • It produces specialized structures called appressoria that physically penetrate the hard eggshell or the protective body wall of adult female nematodes.

  • Once inside, it colonizes the contents (eggs or female body) with hyphae, digesting and absorbing nutrients, thereby killing the next generation.

• Secondary Mechanisms:

  • Enzyme Production: It secretes a suite of enzymes (chitinases, proteases, lipases) that degrade the chitin and protein matrices of the eggshell, facilitating penetration.

  • Plant Growth Promotion: As an endophyte, it can enhance root growth and improve plant nutrient uptake, indirectly helping plants tolerate nematode damage.

  • Nematicidal Metabolites: Some strains produce compounds that can paralyze or kill juvenile nematodes.

3. Advantages as a Biocontrol Agent

• Target Specificity: Primarily affects sedentary nematode parasites, reducing harm to beneficial soil fauna.

• Safety: Non-toxic to mammals, birds, and plants. It is a GRAS (Generally Regarded As Safe) organism.

• Environmental Compatibility: Fits well into integrated pest management (IPM) programs and organic farming systems.

• Durability: Can survive in soil as chlamydospores (thick-walled resting spores) during unfavorable conditions.

• Synergistic Effects: Can be combined with other biocontrol agents (e.g., Trichoderma, Bacillus firmus) or with reduced doses of nematicides.

4. Challenges and Limitations

• Slow Action: Not a quick "knock-down" solution like chemical nematicides. Requires advance application and builds up over time.

• Environmental Sensitivity: Its efficacy is influenced by soil temperature, moisture, pH, and organic matter content. Optimal activity is around 25-30°C and in moist (not waterlogged) soils.

• Host Density Dependence: It is most effective at moderate nematode densities. If nematode populations are too low, the fungus lacks a food base; if too high, it may be overwhelmed.

• Formulation and Shelf-Life: Producing stable, effective, and long-lasting commercial formulations can be challenging.

• Cost and Availability: While commercial products exist (e.g., Klamic®, Rizotec®), they may be more expensive or less readily available than chemicals in some regions.

5. Practical Application in Agriculture

• When to Apply: Best applied preventatively or at early cropping stages—at sowing, transplanting, or into the seed furrow.

• How to Apply: Commercial products come as wettable powders, granules, or alginate pellets. They can be applied via:

  • Soil drenching

  • Seed coating

  • In-furrow application

  • Through drip irrigation systems (if compatible)

• Integration into IPM:

  • Combine with organic amendments (compost, manure) to improve soil conditions for the fungus.

  • Use nematode-resistant varieties alongside the fungus.

  • Implement crop rotation with non-host plants to lower initial nematode populations.

  • Avoid broad-spectrum chemical fungicides in the soil that might inhibit P. chlamydosporia.