Bacillus subtilis is a versatile soil bacterium widely used in agriculture for its multifaceted benefits to plants. It promotes growth, enhances disease resistance, and improves soil health. Below is a concise overview of how plants can benefit from Bacillus subtilis:
Plant Growth Promotion:
Bacillus subtilis produces phytohormones like indole-3-acetic acid (IAA) and gibberellins, which stimulate root and shoot growth, leading to improved nutrient and water uptake.
It solubilizes nutrients such as phosphorus and potassium, making them more available to plants, which enhances growth and yield.
Biocontrol of Pathogens:
The bacterium produces antimicrobial compounds, including lipopeptides (e.g., surfactin, iturin, fengycin) and antibiotics, which suppress soil-borne pathogens like Fusarium, Rhizoctonia, Pythium, and Phytophthora.
It induces systemic resistance (ISR) in plants, boosting their natural defenses against fungal, bacterial, and some viral diseases, reducing issues like root rot, blight, and wilts.
Stress Tolerance:
Bacillus subtilis helps plants tolerate abiotic stresses such as drought, salinity, and heavy metal toxicity by producing enzymes (e.g., ACC deaminase) that reduce stress-induced ethylene levels.
It forms biofilms around roots, enhancing water retention and protecting roots from environmental stressors.
Soil Health Improvement:
The bacterium enhances soil microbial diversity and activity, improving soil structure and fertility by decomposing organic matter and releasing nutrients.
It contributes to bioremediation by degrading pollutants like pesticides and heavy metals, creating a healthier soil environment for plants.
Seed Germination and Vigor:
When applied as a seed treatment, Bacillus subtilis protects seeds from pathogens and promotes faster germination and stronger seedling development.
Applications:
Used as a biofertilizer, biopesticide, or soil amendment in sustainable and organic agriculture to reduce reliance on chemical inputs.
Applied via seed coating, soil drenching, foliar spraying, or root inoculation for optimal results.
Examples:
Studies show Bacillus subtilis improving yields in crops like tomatoes, wheat, rice, and strawberries by enhancing growth and controlling diseases like powdery mildew or root rot.
It’s widely used in greenhouse systems and organic farming to manage soil-borne diseases and promote plant vigor.
Comparison with Other Microorganisms:
Bacillus velezensis: Similar to B. subtilis in producing lipopeptides and promoting growth, but B. velezensis may have a broader spectrum of antimicrobial activity.
Bacillus megaterium: Stronger in phosphorus solubilization, while B. subtilis excels in pathogen suppression and biofilm formation.
Brevibacillus laterosporus: Offers insecticidal properties, unlike B. subtilis, which focuses more on fungal and bacterial pathogens.
Trichoderma harzianum: A fungus with superior mycoparasitic activity against fungal pathogens, while B. subtilis provides broader nutrient and stress benefits.
Bacillus thuringiensis: Specializes in insect pest control with Cry toxins, whereas B. subtilis targets pathogens and promotes growth.