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Mass Production and Agricultural Benefits of Vesicular-Arbuscular Mycorrhizal Fungi (VAM)

Comprehensive overview of VAM fungi morphology, isolation, mass production techniques, field application methods, and their critical role in enhancing crop growth, nutrient uptake, stress tolerance, and soil fertility.

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Mass Production of Mycorrhiza Dr.M.Jothimuniyandi
Vesicular–Arbuscular Mycorrhizal fungi • The vesicular–arbuscular mycorrhizal fungi (VAM fungi) are a group of symbiotic, endotrophic mycorrhizal fungi that live in association with the roots of higher plants. They belong to the family Endogonaceae under the class Zygomycetes. These fungi penetrate the root cortex and form specialized structures called vesicles and arbuscules, which facilitate the exchange of nutrients between the fungus and the host plant. • Examples: Glomus, Gigaspora, Acaulospora, Sclerocystis, and Endogone.
VAM fungi • VAM fungi are associated with numerous economically important crop plants, including rice, maize, potato, soybean, cotton, tobacco, sugarcane, tomato, rubber, strawberry, citrus, avocado, coffee, tea, cocoa, peas, apple, and papaya. Through this association, the fungi enhance nutrient uptake, improve plant growth and increase tolerance to environmental stresses.
Morphology of VAM VAM fungi possess three important structures: • External Hyphae • Aseptate, branched fungal filaments extending from the root into the soil. • Absorb water and nutrients from the soil. • Arbuscules • Highly branched, tree-like structures formed inside cortical cells of roots. • Serve as the site of nutrient exchange between fungus and host plant. • Vesicles • Spherical or oval, thick-walled structures formed within or between root cortical cells. • Act as storage organs containing reserve food materials. Spores (Chlamydospores) • Thick-walled reproductive structures produced in soil. • Used as inoculum for the mass production of VAM fungi.
Isolation of VAM Spores VAM spores are isolated from the soil in two ways: • Sieving method • Floatation method
Sieving method This method separates spores based on their physical size using a graduated series of mesh screens. • Pre-treatment: A known quantity of soil is mixed with warm water (40–50°C) and stirred vigorously to break down soil aggregates and release the spores trapped in the soil matrix. • Settling: Heavy sand and gravel particles are allowed to settle to the bottom of the container for a few seconds. • Graduated Sieving: The suspended liquid (containing spores and lighter organic matter) is decanted through a stacked series of sieves. Typical mesh sizes used to catch debris and larger spores include 719μm, 250μm, and 75μm. • Collection: The final filtrate is passed through a fine 45μm sieve, which catches the target VAM spores. • Drying: The collected spores are rinsed off the sieve and dried in the shade to maintain viability for starter cultures.
Floatation method This method separates spores from remaining soil debris based on their specific gravity. • Initial Filtering: Soil is blended with water and passed through a coarse sieve to remove large stones and root fragments. • Density Gradient Preparation: A centrifuge tube is prepared with layers of varying sucrose concentrations (typically ranging from 20% to 60%). • Centrifugation: The soil suspension is layered on top and centrifuged (typically at higher speeds like 2000–3000 rpm for 3–5 minutes, though low-speed variations exist). • Spore Recovery: Due to their buoyancy, the clean VAM spores cleanly concentrate at the interface between the 20% and 60% sucrose layers. They are pipetted out, rinsed thoroughly with distilled water to remove sugar residues, and dried.
Mass Production of Mycorrhizae (VAM) • The VAM spores are immersed in a solution containing chloramin-T and streptomycin (200 ppm) for 15 minutes and then washed with distilled water. • The spores are mixed with sterilized soil. The soil is filled in pots and seedlings of a host plant are transplanted into the pots. • The pots are kept in a greenhouse for 3–4 months. • Finally, the soil in the pots along with the roots of host plants is macerated and dried until it attains 5% moisture. • The dried soil–inoculant mixture is used for field application. BAIF Research Foundation, Pune has used Vermiculite + Peat (4:1) as a substrate and Bahia grass and Guinea grass as hosts for the mass production of Glomus and Gigaspora.
Mass Production of Mycorrhizae (VAM) Steps involved in the mass production of VAM fungal inoculum
Field Application The dried soil-root-inoculant mixture can be introduced to crops using two main delivery techniques: Seed Pelleting (Targeted Application) • The VAM inoculant is suspended in a water or slurry adhesive (like carboxymethyl cellulose or gum arabic). • Seeds are mixed into this slurry to create a uniform fungal pellet coating around each seed. • Advantage: When the seed germinates, the emerging radical immediately comes into contact with the VAM spores, ensuring rapid, early-stage root colonization. Soil Broadcasting (Area Application) • The inoculant is evenly spread across the entire field surface just prior to the final ploughing or discing stage. • Advantage: Distributes the fungi throughout the topsoil layer, making it ideal for fields utilizing direct transplantation of seedlings (e.g., vegetable crops or rice) or for treating large acreage quickly.
Importance of VAM Fungi 1. Enhanced Nutrient Uptake • Improves absorption of P, Zn, S, Cu, Ca, K, Fe, Mn, and Br from soil. 2. Increased Plant Growth • Promotes growth and vigor in crops such as: • Citrus • Maize • Wheat • Barley 3. Improved Water Absorption • Enhances water uptake. • Helps plants withstand drought and water stress. 4. Increased Chlorophyll and Cytokinin Content • Improves photosynthetic efficiency and overall plant health.
Importance of VAM Fungi 5. Salt and Heavy Metal Tolerance • Reduces crop sensitivity to salinity and heavy metal toxicity. 6. Improved Transplant Survival • Functions as extra root hairs and improves hardiness of transplant stocks. • Example: Pine. 7. Disease Resistance • Protects plants against soil-borne pathogens causing root diseases. 8. Reduction of Stunted Growth • Reduces growth inhibition in fumigated or nutrient-deficient soils.
Importance of VAM Fungi 9. Increased Crop Yield • Enhances yield in crops such as: • Potato • Maize • Barley • Wheat • Sugarcane 10. Support During Nutrient Stress • Helps plants survive nutrient-deficient conditions by improving nutrient acquisition. 11. Improved Soil Fertility • Enhances soil aggregation and beneficial microbial activity. 12. Reduced Fertilizer Requirement • Particularly reduces the need for phosphorus fertilizers. 13. Forestry and Horticultural Applications • Widely used in: • Forest nurseries • Fruit crops • Plantation crops • Reforestation programs