Mycorrhiza (VAM)

Introduction

Vesicular Arbuscular Mycorrhizae (VAM), a type of endomycorrhizal fungi, form symbiotic associations with the roots of over 80% of terrestrial plant species. These fungi are critical for improving phosphorus uptake, enhancing root systems, and increasing plant resistance to environmental stress. VAM is a cornerstone of sustainable soil fertility management, particularly in low-input and organic farming systems.

Scientific Description

VAM fungi belong to the phylum Glomeromycota, with key genera including Glomus, Rhizophagus, and Acaulospora. They colonize the cortical cells of plant roots, forming arbuscules (branched hyphal structures for nutrient exchange) and vesicles (storage structures). They extend hyphae far beyond the root zone, accessing phosphorus and micronutrients otherwise unavailable to plants.

Core biological features:

• Phosphorus Mobilization: Solubilizes and translocates immobile forms of P (especially in acidic and alkaline soils).
• Enhanced Root Absorption: Increases root surface area via external hyphal networks.
• Improved Soil Aggregation: Excretes glomalin, a glycoprotein that helps bind soil particles.
• Water & Stress Management: Helps plants withstand drought, salinity, and heavy metals.
• Symbiotic Only: Cannot live saprophytically — requires living roots for propagation.

Benefits

• Boosts Phosphorus Uptake: Extends effective root volume to reach P beyond depletion zones.
• Improves Water Absorption: Critical during drought or poor irrigation conditions.
• Enhances Soil Structure: Promotes stable aggregates and reduces erosion.
• Increases Plant Biomass: Supports vigorous growth, especially in nutrient-deficient soils.
• Supports Other Microbes: Synergistic with Azospirillum, Rhizobium, Bacillus, and Trichoderma.
• Long-Term Soil Health: Residual benefits continue in multi-season cropping systems.

Uses

• Crops Benefited: Almost all non-Brassicaceae crops — cereals, pulses, vegetables, fruit trees, sugarcane, spices, plantation crops.
• Application Methods:
  • Soil mixing: 2–5 kg/acre with compost or nursery soil
  • Root dipping: For vegetable seedlings and orchard saplings
  • Pelleting: Used to coat seeds for large-scale planting
• Ideal Conditions: Works best in soils with moderate organic matter and low to medium available phosphorus.
• Incompatible With: Excessive phosphorus fertilizer application (P > 40 kg/ha can suppress colonization)

Trivia

• Mycorrhizae are older than plants themselves — their fossil record dates back over 400 million years.
• VAM fungi cannot be cultured without plant roots, making production more complex than bacterial biofertilizers.
• The glomalin they produce contributes significantly to carbon sequestration in soil.
• Some organic farming certifications require mycorrhizal inoculation in orchard and perennial systems.