📈 Biological Control of Plant Diseases
Biological Control of Plant Diseases.
Biological control (biocontrol) involves the use of living organisms or their products to suppress plant pathogens and reduce disease incidence. It is a cornerstone of sustainable IPDM because it minimizes chemical inputs and preserves ecosystem balance.
Mechanisms of Biocontrol
Biocontrol agents (BCAs) suppress pathogens through several mechanisms:
Direct Mechanisms
- Mycoparasitism — the BCA directly parasitizes the pathogen. Trichoderma spp. coil around and penetrate hyphae of Rhizoctonia and Sclerotium.
- Antibiosis — production of antimicrobial compounds. Pseudomonas fluorescens produces 2,4-DAPG (2,4-diacetylphloroglucinol) and phenazines that inhibit fungal growth.
- Competition — BCAs compete for nutrients and ecological niches. Non-pathogenic Fusarium spp. colonize root surfaces, excluding pathogenic strains.
- Lytic enzyme production — chitinases, glucanases, and proteases degrade pathogen cell walls.
Indirect Mechanisms
- Induced Systemic Resistance (ISR) — BCAs trigger defense responses in the host plant through jasmonic acid and ethylene signaling pathways.
- Plant Growth Promotion — PGPR (Plant Growth-Promoting Rhizobacteria) enhance root development and nutrient uptake, making plants more resilient.
Major Biocontrol Agents
| Agent | Target Pathogens | Application |
|---|---|---|
| Trichoderma viride | Rhizoctonia, Sclerotium, Fusarium | Seed treatment, soil application |
| Trichoderma harzianum | Broad-spectrum soil-borne fungi | Soil drenching, composting |
| Pseudomonas fluorescens | Pythium, Fusarium, bacterial wilt | Seed coating, root dipping |
| Bacillus subtilis | Powdery mildew, damping-off | Foliar spray, seed treatment |
| Ampelomyces quisqualis | Powdery mildew fungi | Foliar application |
| Agrobacterium radiobacter K84 | Crown gall (A. tumefaciens) | Root dipping before transplanting |
Formulation and Delivery
BCAs are commercially available as:
- Talc-based powder — mixed with seed or soil
- Wettable powder — for foliar sprays
- Liquid formulations — for drip irrigation and drenching
- Granular formulations — for soil incorporation
Shelf life and viability are critical — most formulations require cool, dry storage and have a shelf life of 6-12 months.
Limitations
- Performance is environment-dependent — temperature, moisture, and soil type affect BCA establishment
- Slower action compared to chemical fungicides
- Inconsistent results under high disease pressure
- Requires farmer training for proper handling and application
Integration with IPDM
Biocontrol is most effective when combined with cultural practices (organic amendments that support BCA populations), resistant varieties, and minimal chemical use. Fungicide compatibility must be verified, as many chemicals are toxic to BCAs.
Summary Cheat Sheet
Mechanism Snapshot
| Mechanism | Key Effect |
|---|---|
| Mycoparasitism | Direct attack on pathogen hyphae |
| Antibiosis | Antimicrobial metabolite production |
| Competition | Niche and nutrient exclusion |
| ISR | Host defense priming |
Fast Recall
- Common biocontrol genera: Trichoderma, Pseudomonas, Bacillus.
- Delivery routes include seed treatment, soil application, and foliar spray.
- Field success depends strongly on environment and formulation viability.
Exam Traps
- Biocontrol is not instant knockdown like many fungicides.
- Fungicide compatibility must be checked before tank use.
- Storage conditions directly affect efficacy.
References
2 sources • [1] [2]
References
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