Mycorrhiza is a distinctive morphological structure that grows as a result of a mutualistic symbiotic relationship between plant roots and some root-inhabiting fungi. These symbiotic associations are found in about 90% of all land plants and have been around for approximately 400 million years.
The fungus connects with the plant root zone (rhizosphere), with its large network of hyphae, thus effectively increasing the surface area for water & nutrient absorption by plants. These hyphae deliver water and available nutrients directly to the plant roots in exchange for carbohydrates from the plants in the form of root exudates.
The mycorrhiza bio-fertilizer regulate biological activities, improve soil fertility, soil health, and uptake of plant nutrient, enhance plant growth in acidic and saline soils, water stress and flooded conditions, tolerance of drought, and salinity and transplantation shock. It also induces resistance in plants to soil-borne diseases. It reduces the dosage requirement of phosphatic fertilizers and other micronutrients. Mycorrhiza fungus hyphae proliferate beyond the nutrient depletion zone reaching the source of the nutrient.
Types of Mycorrhiza
- Ectomycorrhiza: It is present among angiosperms and gymnosperms. In the roots of higher plants mostly root hairs are absent. Therefore, the roots are infected by mycorrhizal fungi which, in turn, replace the root hairs and form a mantle. The hyphae grow inter-cellularly and develop in the cortex. Thus, a bridge is created between the soil and root through the mycelia.
- Endomycorrhiza: The morphology of these roots, even after infection, remains unchanged. Root hairs develop in a normal way. The fungi are individually present on the root surface. They also penetrate the cortical cells and get grow intra-cellular by secreting extracellular enzymes. Endomycorrhizas are found in all groups of the plant kingdom.
- Ectendomycorrhiza: In some gymnosperms and angiosperms, ectotrophic fungal infections occur. Hyphae are established intracellularly in cortical cells. Thus, symbiotic relation develops similar to ecto- and endo-mycorrhizas.
Advantages
- Mycorrhiza enhances water and nutrient uptake in plants and increases flowering and fruiting. There is a reduction in irrigation requirements and the need for chemical fertilizer.
- The plant has increased drought and pathogen resistance.
- The water infiltration and water holding capacity of the soil increases
- It promotes high microbial activity and nutrient cycling in the soil which leads to better root development.
- Overall mycorrhiza increases plant health and stress tolerance.
Vesicular Arbuscular Mycorrhiza (VAM):
VAM is a group of root obligate biotrophs that exchange mutual benefits with about 80% of plants. They are considered natural biofertilizers, since they provide the host with water, nutrients, and pathogen protection, in exchange for photosynthetic products. They form a network of fine filaments that associate with plant roots and draw nutrients and water from the soil that the root system would not be able to access otherwise.
Different research studies conducted on VAM during the past two decades have highlighted their countless benefits on soil health and crop productivity. It enhances the concentration of various macro-nutrients and micro-nutrients significantly, which leads to increased photosynthate production and hence increased biomass accumulation. Increased photosynthetic activities and other leaf functions are directly related to improved growth frequency of VAM that is directly linked to the uptake of N, P, and carbon, which move towards roots and promote the development of tubers. It has been observed to maintain P and N uptake ultimately helping in plant development at higher and lower P levels under different irrigation regimes. The AMF extra-radical hyphae can absorb and assimilate inorganic N and can provide 20-75% of the total N needed for the host plant. Dr. Bona observed the beneficial effects of VAM on the quality of tomatoes. Another study, reported increased contents of sugars, organic acids, vitamin C, flavonoids, and minerals resulting in enhanced citrus fruit quality. Mycorrhizal symbiosis induces enhanced accumulation of anthocyanins, chlorophyll, carotenoids, total soluble phenolics, tocopherols, and various mineral nutrients. It has been employed in large-scale field production of maize, yam, and potato, confirming that VAM possesses a considerable potential for enhancing crop yield.
