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VAM / Arbuscular mycorrhiza

Vesicular Arbuscular Mycorrhiza (VAM, now more commonly Arbuscular Mycorrhizal Fungi or AMF) is a symbiotic association between specific phycomycete fungi (mainly genus Glomus) and plant roots. The fungus colonises root cortical cells, forming the characteristic vesicles (storage structures) and arbuscules (nutrient-exchange structures), while extending an extensive network of extramatrical hyphae into the soil. The symbiosis is one of the most ancient and widespread plant-microbe partnerships, occurring in over 80% of terrestrial plant families.

Composition

  • Active organism: Glomus species and related Glomeromycota fungi
  • Form: carrier-based (vermiculite, peat) inoculant containing colonised root fragments, spores and hyphal propagules
  • Indian sources: ICAR-IIHR and ICAR-IIOPR have developed VAM consortia used in horticulture and plantation crops including oil palm
  • Regulator: FCO biofertiliser schedule

Mode of action

The fungal hyphae extend the effective root absorbing surface by 10-1000 fold, allowing the plant to explore a much larger soil volume than its own root system can reach. The primary nutritional benefit is enhanced phosphorus uptake, including from forms of soil P that are not available to roots directly. VAM also improves uptake of zinc, sulphur and nitrogen, and confers secondary benefits in drought tolerance, salinity tolerance, soil-aggregate stability and resistance to several soil-borne diseases.

Target use and dose

  • Seedling root dip (vegetable nursery, paddy nursery): 100-200 g per litre of slurry.
  • Soil application: 4-10 kg per acre mixed with FYM at land preparation.
  • Planting pit (orchard, plantation): 50-100 g per pit, mixed with soil and FYM.

Effects are largest on P-deficient soils with low to moderate organic matter; on already-fertilised soils with high water-soluble P (from heavy DAP or SSP application), the symbiosis is partially suppressed and the benefit is reduced.

Safety and regulatory status

Notified under FCO Schedule III biofertilisers; non-pathogenic. Should be applied with adequate soil moisture for establishment and should not be combined with chemical fungicides that kill fungal propagules.

See also: Microbial Biofertilizers, Azotobacter Biofertilizer, Liquid Organic Biofertilizer Consortia, Dap, Ssp Single Super Phosphate.

References

  1. Mycorrhiza VAM Biofertilizer. ICAR Indian Farming.
  2. VAM as Biofertilizer for Horticulture. Springer.