Arbuscular Mycorrhizal Fungi (AMF) constitute a group of root obligate biotrophs that exchange mutual benefits with about 80% of plants. They are naturally considered as biofertilizers, since they provide the host with water, nutrients, and pathogen protection, in return for photosynthetic products.

 Arbuscular mycorrhizal fungi produce highly branched fungal structures, arbuscules, within root cortical cells of their host plants, with which they exchange inorganic minerals, especially phosphorus and carbon compounds. One of the most abundant organisms in the rhizosphere is the arbuscular mycorrhizal fungi and the relationships can be found within a broad range of more than 200,000 species of host plants.

Despite their abundance and wide range of relationships with plant species, arbuscular mycorrhizal fungi have been known to show low species diversity and only approximately 240 species have been described within a fungal phylum.

The arbuscular mycorrhizae fungus-plant association is a mutually beneficial event: The plant supplies the fungus with carbon (from its fixed photosynthates) while the fungus in turn assists the plant in its uptake of phosphate and other mineral nutrients from the soil. These bi-directional exchanges of nutrients occur through extensively branched haustoria, called arbuscules. In addition to increased nutrition, increased resistance by mycorrhizal plants is shown to root pathogens and tolerance to drought stress and their hormonal balance is disrupted.

Arbuscular mycorrhizae fungi are soil-borne fungi that can significantly improve plant nutrient uptake and resistance to several abiotic stress factors. A majority of the species of arbuscular mycorrhizal fungi belong to the sub-phylum Glomeromycotina, of the phylum Mucoromycota.

Four orders of arbuscular mycorrhizae fungi, namely, Glomerales, Archaeosporales, Paraglomerales, and Diversisporales, have been identified in this sub-phylum that also include 25 genera. They are obligate biotrophs and ingest plant photosynthetic products and lipids to complete their life cycle.

Arbuscular mycorrhizae fungi-mediated growth promotion is not just by improving water and mineral nutrient uptake from the adjoining soil but also by protecting the plants from fungal pathogens. Therefore, arbuscular mycorrhizae fungi are vital endosymbionts which play an effective role in plant productivity and the functioning of the ecosystem. They are of key importance for sustainable crop improvement.

The symbiotic association of arbuscular mycorrhizae fungi is a typical example of a mutualistic relationship, which can regulate the growth and development of plants. The mycelial network of fungi extends under the roots of the plant and promotes nutrient uptake that is otherwise not available. The fungal mycelium colonizes the roots of many plants even if they belong to different species, resulting in a common mycorrhizal network (CMN).

This CMN is considered as a primary component of the terrestrial ecosystem with its significant effects on different plant communities, particularly on invasive plants and the fungal-mediated transport of phosphorus (P) and nitrogen (N) to plants. Moreover, communal nutrients also relocate from fungi to the plant, along with other associated effects, which is probably why AMF improve plant tolerance to biotic and abiotic factors.

They can improve the characteristics of soil and consequently encourage plant development in normal as well as in stressful circumstances. AMF colonization improves the tolerance of plants to stressful cues by bringing about several changes in their morpho-physiological traits. AMF are considered as natural growth regulators of a majority of terrestrial flora. AMF are used as bio-inoculants, and researchers encourage their use as prominent bio-fertilizers in sustainable crop production.

Furthermore, AMF-inoculated soil forms more constant masses and significantly higher extra-radical hyphal mycelium than the non-AMF-treated soils. Glomalin-related soil protein (GRSP) is believed to maintain water content in soils exposed to different abiotic stresses, which later on regulates water frequencies between soil and plants, automatically triggering plant development.

Glomalin contains 30–40% C and its related compounds that protect soil from desiccation by enhancing the soil water holding capacity. Growth-related functions, for example, stomatal conductance, leaf water potential, relative water content (RWC), PSII efficiency, and CO2 assimilation are affected by AMF inoculation. AMF also help improve water stress tolerance by physiological alteration of the above-ground organs and tissue.

Furthermore, the inoculation of AMF improves the accumulation of dry matter and enhances water moisture uptake, thereby improving plant tolerance against stresses like drought and salinity. The exploitation of AMF for plant growth in various biological ecosystems can contribute greatly to organic culturing for growth promotion and yield maximization.

The Glomeromycota are not as diverse as other phyla of fungi nor are there as many species. However, they make up for this uniformity by being among the most abundant and widespread of all fungi. As far as we know, all species of Glomeromycota are mutualistic with plants, forming arbuscular mycorrhizae.

These fungi were considered to be members of the Zygomycota for many years, mainly because their hyphae lack septa and because their spores may superficially resemble zygospores. More recent genetic evidence shows that they are quite distinct from other fungi and belong in a separate phylum. Paleontologists have suspected this for a long time. The fossil roots of plants known to be as old as 450 million years contain the hyphae and spores of Glomeromycota, showing this group to be among the oldest of fungi.

Mycorrhizae formed by Glomeromycota are found in the majority of land plants. Not surprisingly their spores are not very difficult to find in the soil. These spores are larger than most fungal spores and can often be found using a low-power dissecting microscope.

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