Asian Soybean Rust (ASR), caused by the obligate biotrophic fungus Phakopsora pachyrhizi, is one of the most destructive foliar diseases impacting global soybean production. Since this pathogen rapidly develops resistance to chemical fungicides, biological control methods utilizing beneficial microorganisms and their metabolites have become vital for sustainable disease management.
Core Biocontrol Agents (Microbial Biopesticides)
🟩 Bacillus Species (Bacterial Antagonists)
- Bacillus subtilis: The most commercially mature bacterial solution. It competes aggressively for space and nutrients on the leaf surface and secretes lipopeptides (such as Surfactin) that disrupt rust urediniospores’ cell membranes. Field trials show that alternating B. subtilis with chemical fungicides reduces the ASR disease index by 41% to 69%.
- Bacillus velezensis: Produces a broad spectrum of antifungal lipopeptides that strongly inhibit rust spore germination and germ tube elongation.
🟩 Metarhizium Species (Entomopathogenic & Antifungal Fungi)
- Metarhizium anisopliae & Metarhizium humberi: Recent research highlights that their cell-free culture filtrates are rich in bioactive metabolites. These filtrates inhibit P. pachyrhizi urediniospore germination by 85% to 96%.
- Dual-Action Protection: Applying Metarhizium reduces the fungal biomass of ASR within soybean leaves by roughly 30%, while simultaneously controlling major insect pests like soybean loopers and caterpillars.
🟩 Trichoderma Species (Hyperparasitic Fungi)
- Trichoderma harzianum: Acts as a direct hyperparasite. It coils around and penetrates the rust pustules (uredinia), secreting chitinases and β-1,3-glucanases to degrade the rust cell walls while simultaneously triggering the plant’s Induced Systemic Resistance (ISR).
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