Beneficial fungal communities from different habitats and their roles in plant growth promotion and soil health

Microbes are ubiquitous in nature, and plant-microbe interactions are a key strategy for colonizing diverse habitats. Fungi are producing a wide range of secondary metabolites and bioactive compounds, which are probable alternative sources of drugs and/or antibiotics. Fungi are associated with the crops and plays an important role in plant growth promotion and enhanced soil fertility using different PGP mechanism such as solubilization of phosphorus, zinc, potassium; production of plant growth regulator (auxins, cytokinin, gibberellins, ethylene and abscisic acid); hydrolytic enzymes (xylanases, laccase, pectinases, cellulases); and siderophores. Besides eliciting plant defence reaction against pathogens; PGP fungi also help in plant growth promotion and alleviation of different abiotic stresses under harsh environments. The PGP fungi have reported from different genera of phyla Chytridiomycota, Zygomycota, Glomeromycota, Ascomycota, and Basidiomycota. Fungi also have significant potential applications in various industries like medical, and food. In the medical applications, fungi and fungal products are used to control disease in human and animals. In the fermentation industries fungi used to make alcoholic beverages, cheeses, bread, kefir, yogurt and various other food preparations and the agricultural sectors used to make plant healthy and protects to pathogens. The present review, deals with the biodiversity of beneficial fungi from different habitats and their biotechnological applications in plant growth promotion and soil health. Published by Arab Society for Fungal Conservation


Introduction
Fungi are one of the most important taxonomic groups of microbes that exists on the whole world that is eukaryotic and heterotrophic living organism; including mildews, molds, mushroom, yeast and also puffballs. They are beneficial for plant growth and crop production as well as crop protections. Fungi have been reported from victorious soil, water, dead and decaying, organic matters and skin of animal's inhabitant that has high capacity and flexibility to uptake diverse undesirable or unfavourable conditions (Karun et al. 2018;Rana et al. 2019). They are found in different habitats such as water, soil, animals, dead matter, deserts and many are symbionts of plants but mostly grown in land environments but in which some species are growing aquatic habitats like (Deep oceans, seas and coral reefs, glaciers and hot spring) and as extreme environments (acidic, alkaline, drought, pressure, salinity, and temperatures) and associated with plants (epiphytic, endophytic, and rhizospheric) and human (Blanchette et al. 2017;Mouchacca 2016;Rashad and Abdel-Azeem 2017;Yadav et al. 2017a).
The beneficial fungi promotes the plant via directed multifarious plant growth-promoting (PGP) attributes including micronutrients solubilization (phosphorus, potassium and zinc), and production of plant growth regulators like auxin, gibberellins, cytokinin and ethylene or indirectly via the production of siderophores, 22 antagonistic substances, antibiotic, and synthesis of cell wall lysing enzymes like cellulases, gluconase, and glycosidase (Abo Nouh 2019; Urja and Meenu 2010).
Fungi play significant roles in agriculture, medicine and industry in different processes for sustainable development. In the medical field, fungi and their products are used for control disease in human and animals. They are involved in industrial processing make the 10 to 20 most beneficial products for human health, drug discovery research is ongoing and it is essential for daily human life. Mycorrhizal fungi are essential for the growth of plants. It is used as a food and also used to make fermentation products like alcoholic beverages, cheeses, bread, kefir, yogurt and various other food preparations (Abo Nahas 2019; Kotowski 2019; Rana et al. 2020b;Yadav 2019). The increasing demand for food to feed the growing population, organic and sustainable farming practice is required. The beneficial fungi have been used plant growth promotion and development for sustainable agriculture. The fungi are potentially useful for improving plant growth and health, nutrients availability, water uptake, stress tolerance and as well as biocontrol (Yadav et al. 2020a;Yadav et al. 2020b). Now a day's fungi are used in many regions of the world as a biological pest control. Beneficial fungi play a significant role in numerous physiological processes, including minerals and water uptake, stomatal movements, photosynthesis and biosynthesis of compounds and in mitigation to environmental stresses like drought, heat, salinity, cold and heavy metals (Abdel-Salam et al. 2017;Begum et al. 2019). The fungi could be applied as inoculants in the fields for crop production and protection. Mycofungicides and fungal biofertilizers were helped for agricultural uses to manage plant diseases as well as the environments defence its capability to improved crop production (Kour et al. 2020b;Suman et al. 2016b).
In recent years, there are different microbial fungicides have been developed like Ch. cupreum, Promote® developed from Trichoderma harzianum, T. viride, SoilGard® made from Gliocladium virens, Trichodex® work out from T. harzianum and Ketomium®, constructed from Chaetomium globosum (Kaewchai 2009). The fungal biofertilizers with multifarious PGP attributes have been reported e.g. Trichoderma, mycorrhizal fungi (arbuscular mycorrhizae e.g. Glomus intraradices),ectomycorrhiza (Pisolithus tinctonus) and which form mutualistic associated with plants, whereas, Glomus sp. or Trichoderma sp. suppressed pathogens of fungal and species of Trichoderma (T. asperellum, T. atroviride, T. harzianum, T. virens, and T. viride) are commonly used in biocontrol and are known as biostimulants for horticultural/agricultural crops. Fungal biofertilizers play a vital role in promoting plant growth, health and productivity as well as improving soil fertility (Frąc et al. 2018;Rana et al. 2019). The present review, deals with the biodiversity of beneficial fungi from different habitats and their biotechnological applications in plant growth promotion and soil health.

Biodiversity of fungal community
In microbial ecology, diversity and distribution of microorganisms or microbes is one of the debated points and among them, the trending topic in this is fungi. Fungi, the decomposers, mutualisms, and pathogens are known to be extremely diverse. So far, total 712,000 fungal species both beneficial and pathogenic; have been known across the board (Schmit and Mueller 2007). These known fungal species were identified from the different regions like air, soil, plant-associated and various extreme environments such as deep oceans, hot springs, glaciers, deserts, mine and coastal region (saline areas) (Kour et al. 2019a;Sharma et al. 2019b;Rana et al. 2020a).
On review of different research on fungal diversity from diverse habitats, it is found that fungi reported are belonged to three different phyla (Figure 1) namely, Ascomycota, Basidomycota and Mucoromycotaand for more details check table (1) in supplementary materials.
The genera belong to phylum ascomycota are predominant. The abundance and relative distribution show that species of genera of genera Aspergillus are the most dominant ( Figure 2).

Plant associated fungal communities
Plants, the recognized meta-organism, possess an association with distinct microbiome without which their life support function like nutrient acquisition, protection against environmental stress will not work. Within all microbes, fungi are also associated with the plants and in every plant, harbour has been symbiotically associated with particular fungi species, which fulfil the requirement of the host. In general, associated fungi are present in the three different plants regions (below and above ground) named as epiphytic or phyllosphere, endophytic and rhizosphere (Subrahmanyam et al. 2020;Tiwari et al. 2020;Yadav et al. 2018a).
Epiphytic or phyllosphere region of plant is comprised of aerial parts, especially leaves, and is a common niche for synergism between plant and fungi. The epiphytic region of the plants is exposed to the air and dust that result in the establishment of typical flora of fungi, which is aided by the waxes, cuticles and appendages. The fungi survive on the aerial parts of plants because they contain 23 nutrients factors like sucrose, fructose, glucose and amino acids and in return fungi protect the plants from various air borne pathogens and helps in plant growth promotion. The fungi present in the phyllospheric region are also known as extremophiles as they survive in low/high temperature (5-55°C) and harmful UV radiations  Another very unique region of plants where fungi colonize is the endophytic region. This region of plant is referred to the interior parts like seed, stem and roots. The fungi residing in internal plant parts don't cause any pathogenic effects and lives in symbiotically (Bacon and White 2000), but during host senescence they may act as pathogens (Rodriguez et al. 2008). These types of fungi present inside the plant may be transmitted from the previous generation via seed, which is known as vertical transmission, or can be transmitted horizontally through the airborne spores (Hartley and Gange 2009), which produces certain cellulolytic enzymes, which is required for the hydrolyses of exothermal walls, such as endoglucanases and endopolygalacturonidases in order to penetrate inside the host plant (Suman et al. 2016a (Yehia et al. 2020).
The third and very important region of plant is rhizosphere. Rhizosphere is the soil zone, which is influenced by the roots. In this region fungi or other microbes are attracted by the rhizodeposits known as exudates, which contains variety of compounds like sugars, organic acids, vitamins, hormones, amino acids, growth hormones, fatty acids and antimicrobial compounds. These compounds are used by the fungi as source of energy and derive maximum benefits and in reverse fungi promote plant growth directly by producing micro and macro-nutrients and indirectly by providing antagonist compounds . A number of microbes from this region is have been reported such as Penicillium sp., Trichoderma sp. (Murali et al. 2012

Fungal communities from extreme habitats
Fungi are ubiquitous, occupy a wide range of ecological niches and extreme habitats are one of that. Earth is surrounded by various types of ecosystem, and one of the unique habitats is extreme environments. The extreme environment included xerophilic, thermophilic (temperature 115°C), psychrophilic (temperature −2-20°C), halophilic (10-30% NaCl), alkalophilic (pH 9) and acidophilic (pH less than 4). These are the environment where normal life hardly exists, but it is a harbour of microbial diversity. Bacteria, archaea and fungi are the microbes that mostly survive in such harsh conditions. All these living organisms so as fungi that survive at such extreme conditions have special features that allow them to live in such habitats (Yadav 2017).
Temperature extremes are the conditions where fungi grow over a wide range. Temperature extreme can high temperature above 115°C and the fungi survive at such a high temperature are known as thermophilic fungi.    (Yang et al. 2020). Another temperature extreme is psychrophilic fungi that survive at the temperature range of −2-20°C. Fungi like Thelebolus sp. (Mukhopadhyay et al. 2014), Dothideomycetes sp.., Phoma herbarum, and Phomasp. (Moghaddam and Soltani 2014), Vishniacozyma globispora, V. dimennae (Tsuji et al. 2019).
pH extreme i.e. Alkalophilic and Acidophilic extreme habitats where pH can be high and cause alkalophilic conditions and low pH can be set the acidophilic conditions.

Mechanism of plant growth promotion
The mechanism of plant growth-promoting fungi has been involved in both direct and indirect mechanism. Direct mechanism (phosphorus, potassium zinc) and plant growth regulators (auxins, cytokinin, ACC deaminase, gibberellins, ethylene, abscisic acid) as well as production of siderophores (Rastegari et al. 2020;Singh et al. 2020;Yadav et al. 2020e) (Fig.3) and for more details are added into table (2) in supplementary materials.

Phosphorus solubilization
Phosphorus is the second most important macronutrient after nitrogen for the plants. This macronutrient is a plant integral part like chemical structures and make up 0.2% of the plant's dry weight. Ironically, the largest reservoir of phosphorus is soil (400-1200 mg/kg) but in the insoluble form complexes with iron, calcium, aluminium which is not available to the plants (Bhattacharyya and Jha 2012).The soluble form of phosphorus in the soil very low for plants metabolism processes which is not sufficient and its deficiency may cause slower growth and reduced leaf biomass of the plant (Avdalović et al. 2015;Cakmak 2008). To fulfil the requirement several chemical fertilizers were being used which are not eco-friendly. Thus, fungi are considered as an alternative strategy because fungi are natural organism that provides soluble form of phosphorus without harming the environment.
The assimilation of phosphorus from the soil by the fungi is achieved by the production of various organic acids like tartaric acid, succinic acid, oxalic acid, malic acid, 2-ketogluconic acid, glyoxylic acid, gluconic acid, fumaric acid, citric acid and alpha-ketobutyric acid and enzyme phosphatase. All the release compounds solubilize the phosphorus and avail the soluble inorganic form that can be assimilated by the plants.

Potassium solubilization
Potassium is the most abundant macronutrient they play a crucial role in plant growth and development. Those have the capacity to convert insoluble form which mineral potassium is available in to soil (Zeng et al. 2012). The soil was most important to the potassium solubilizing microorganism and they are necessary for potassium cycling(Diep and Hieu 2013). Potassium is the most important part of the microbial communities in soil especially in the rhizosphere and they play the most crucial role in plant growth by solubilization of potassium bearing minerals. Mostly many formers have been used two types of fertilizers including nitrogen and phosphorus. They neglect potassium fertilizer because they are either unaware of K fertilizers value or the price of fertilizer is too high for poor formers to be out of control (Mohammadi and Sohrabi 2012). Therefore, potassium availability has been declining in soil, leading to more crop removal than fertilizer application. In this circumstance potassium solubilizing the microbe's position is gaining importance for sustainable crop production in modern agriculture. These fungus release potassium insoluble form which fungus is also beneficial for plant growth promotion by providing protection against plant pathogen and protecting them from stress condition (Archana et al. 2012;Gundala et al. 2013;Parmar and Sindhu 2013;Prajapati et al. 2013).A significant microbiome have been available in rhizospheric soil and improved plant growth by a number of mechanisms (Glick 2014;Nadeem et al. 2013). For the potassium solubilizination we can use large amount of microorganism like as Aspergillus spp., Agrobacterium tumefaciens, B. pumilus, B. subtilis, B. circulans, B. edaphicus, B. mucilaginosus, Flavobacterium spp. and Rhizobium spp. (Gundala et al. 2013;Keshavarz Zarjani et al. 2013;Maurya et al. 2015;Meena et al. 2014a;Meena et al. 2014b). Some scientist was estimated that bacterial species of Frateuria aurantia can be used as a biofertilizer to reduce approximately 50-60% of potash chemical fertilizer in the soil. This potash-solubilizing biofertilizer can be applied in crop production and yield combination with potassium solubilizing microbiome are Azospririllium, Azotobacter, Azospirillum, Acetobacter and Rhizobium (Bahadur et al. 2016). Chemical fertilizers have slowly begun their side-effects on humans and the environment; however, the potassium solubilizing microbes use as a biofertilizer will sustainably increase the available plant nutrients and crop production. It is most important to perform an effective research work to identify an elite microbial strain capable of quickly solubilizing large quantities of potassium minerals that can conserve our current resources and prevent environment contamination hazards caused by excessive in judicial use of chemical fertilizers. There are available two beneficial fungal communities of Arbuscular mycorrhizal fungi species G. intraradices and G. mosseaewe can be used as inoculants in the soil for the crop development. Lian et al. (2002) was documented very similar findings and revealed that potassium solubilization was improved by thermophilic fungi of Aspergillus fumigates when we were inoculated on minerals of potassium solubilization microbes for plant growth and crop improving quantity. Another important and evolving factor concerning sustainable agriculture is the preparation of biofertilizer by using beneficial fungi (Priyadharsini and Muthukumar 2016;Raghavendra et al. 2016;Yadav and Sidhu 2016). Prajapati et al. (2012) was also reported two potassium solubilizing fungi like as Aspergillus terreus, A. niger, Glomas mosseae, G. intraradices and Penicillium sp. that was isolated from soil andobserved that Aspergillus niger and A. terreus could be solubilized to insoluble from in the soil. After that we were find out that potassium available in highest amount in the soil and shown large quantity in liquid medium by the using of two types of insoluble sources of potassium including potassium aluminium silicate and feldspar. Prajapati et al. (2013) and Sangeeth et al. (2012) also reported that potassium solubilizing fungi divided into two phylum such as Ascomycota and Glomeromycota as well as divided in to five genera Aspergillus, Cladosporium, Fusarium, Glomus and Penicillium it were essential plant growth promotion, and the crop protection (Verma et al. 2017a).In the whole world we are using a huge amount of chemical fertilizer in the sustainable agriculture they have been shown negative effect on the economy, environment and the human health. Generally, potassium solubilizing microbes had available in the market in the form of inoculums and biofertilizer to alleviate restriction of chemical fertilizer. It is an environmentally friendly solution to sustainable food production system in many countries across the globe.

Zinc solubilization
Zinc (Zn) is known to be the 23 rd most abundant element on earth with five stable isotopes (Broadley et al. 2007). Zn plays an important role in many biochemical reactions as it is a structural constituent or a regulatory cofactor for different enzymes and proteins. The significant role of zinc finger as structural motif in regulation of transcription is also well known (Englbrecht et al. 2004). It is a vital nutrient required not only by plants but by humans and microbes. Humans require zinc in minute quantities throughout their lives for proper growth, development and physiological functions (Hambidge and Krebs 2007;Hussain et al. 2018). The deficiency of Zn has been ranked as the fourth main micronutrient deficiency in humans and is known to affect approximately 66% of the world's population (Zhang et al. 2012). The major reason behind deficiency is its inadequate intake (Cakmak 2010). Its deficiency in humans leads to various abnormalities in growth, immunity and brain development. Zn deficiency in fungi and bacteria causes impairment in formation of pigments including melanin, prodigiosin and subtilisin (Sindhu et al. 2019). Plants require zinc for regulation of cofactors for range of enzymes which are involved in maintenance of cellular membrane integrity, carbohydrate metabolism, regulation of auxin synthesis, pollen formation and protein synthesis (Alloway 2008). The deficiency leads to smaller leaves, stunted growth, shortened internodes and petioles, chlorosis, and spikelet sterility. Further, it negatively affects the equality of grains and plants become susceptible to infections and injuries (Cakmak 2010).
Deficiency of Zn in different members of community including animals and humans is manifestation of Zn deficiency in the crops that actually supply the community (Saravanan et al. 2011). The worldwide prevalence of Zn deficiency in crops is due to low solubility rather low Zn availability in soil (Iqbal et al. 2010). The soluble zinc sulphate is used as fertilizer to improve plant growth and productivity, but still there are constraints faced in absorbing zinc from the soil due to Zn fixation due to which it becomes unavailable for plant absorption. Zn-solubilizing microbes have great potential as compared to agrochemicals for improving the bioavailability of Zn (Yadav et al. 2020d). The use of microbes is gaining a greater attention in enhancing the crop productivity and restoration of soil fertility (Kumawat et al. 2019). Fungi have an immense potential of solubilizing Zn and tolerating high zinc level. Aspergillus niger was found to grow under 1000 mg Zn, and this fungus is in fact used for quantification of Zn in soils containing low zinc (van Beelen and Fleuren-Kemilä 1997).
Fungi produce organic acids to increase the mobilization of the zinc present in the insoluble form to readily available form in the soil solution (Fomina et al. 2004;Sutjaritvorakul et al. 2017 Yadav et al. 2020c). The inoculation with Zn solubilizing fungi is a potential and eco-friendly technology to increase the bioavailability of native and applied zinc to the plants and an effective alternative to chemical fertilizers.

Phytohormones productions
Broad ranges of microbiome are found in the rhizosphere they are able to produce several kinds of substances that are regulating plant growth and development and phytohormones are one of them. Phytohormones are the plant growth regulating substances that are produced by the plants itself for their proper functioning but in unfavourable conditions they are not able to secrete them. Fungi as well as other microbes have the ability to produce phytohormones such as auxins, abscisic acid, cytokinin, ethylene, gibberellins, jasmonic acid and salicylic acid that can be used by plants. These are play most important role in plant growth and development as well as in plant resistance/tolerance to abiotic stresses and in plant interactions with a variety of mutualistic fungi that can affect cell proliferation in the root architecture by over production of lateral roots and root hairs with a subsequent increase of nutrient and water uptake (Arora et al. 2013).
There are several reports producing phytohormones on plants microbes. The phytohormones producing microbes are inoculation to crop, enhancement of yield, plant growth promotion and development and the increasing soil fertility a for sustainable agriculture (Singh et al. 2017;Yadav et al. 2015a;Yadav et al. 2015b;Yadav et al. 2018b). Usually plant associated microbes develop growth hormones such as auxins and gibberellins.The most common indoleacetic acid (IAA) well known as auxin. When microbes are producing growth regulator hormones, they have been providing the host plant as well as including facilitating root expansion system and many kinds of several benefits. Which increases water and nutrient absorption and improve plant growth and developments that ability to synthesized these phytohormones is generally distributed surrounded by plant associated microorganism and indole acetic acid can be used to promote growth of plants or suppress weeds there are several types of microbial species when are capable of producing the auxins phytohormones IAA . Waqas et al. (2015) reported endophytic fungus of Paecilomyces formosus they play a vital role in heat stress and mitigation of phytohormones and secondary metabolites that were isolated from japonica rice. Gu et al. (2020) had been isolated fungal strain from barley seedling this fungus was named Penicillium citrinum also produce plant growth promoting secondary metabolites and phytohormones.

Auxins
Auxins are the most essential phytohormones they are indole derived hormones and it has been involved plant developmental process including elongation and differentiation, cell division, organ formation, promotes multiple growth and development (Sharma et al. 2019a).
Auxin has also been influencing plant responses to biotic and abiotic stress condition (Peleg and Blumwald 2011). Auxins are synthesized from tryptophan, which is transformed by tryptophan 2-monoxygenase enzymes into indole-3 acetamide. IAA has been synthesized chemically and identically. Ljung (2013) provided strong evidence in support of auxins mediated growth and regulation of development through alteration in pattern of gene expression. There have been many reports are available that depict various modulations in the synthesis, transport, metabolism and behaviour of auxins after plant exposure to stress, however, there are plenty of research reports that support the role of auxin in mediating and improving plant tolerance to abiotic stress (Kazan 2013). Auxins play a significant role in fostering heavy metal tolerance, whether directly or indirectly, as Hu et al. (2013) have been found that heavy metals shown adverse effect on auxin biosynthesis. There were also found in the fungi of Fusarium sp. And it has been reported to participate in the development of fungal auxin (Tsavkelova et al. 2012). However, several pathways have been available for the auxin syntheses were identified in fungi for example Fusarium sp. and Colletotrichum gloeosporioides'auxin are synthesized from same precursors as in microbes indole-3 acetamide but it can also be produce from indole-3 pyruvate, as observed in other fungal genera, for example, Ustilago and Rhizoctonia (Reineke et al. 2008). In addition, a tryptophan independent development of auxins has also been found but the corresponding pathways are still mot well defined. Mehmood et al. (2018) havereported endophytic fungus Fusariun oxysporum they were isolated from maize roots. Endophytic fungi, however, encourage plant growth development and various secondary metabolites; they can help including ammonia and plant hormones, especially Indole acetic acid. (Gu et al. 2020) have been identified Penicillium commune of 112 variants when produce dibberellic acid like as GA3, GA4 and GA7 and other types of GA phytohormes. On the other hand, Babu et al. (2015)documented thatPenicillium menonorum were able to enhance plant growth, development and produce indole-acetic acid (IAA).

Gibberellins
The production of gibberellins is the most important for the root associated microbes and the production of auxins is commonly used to all plant associated microbes like as endophytic, rhizospheric and epiphytic. Gibberellic acid has been found to growth and development of the plants under various condition of abiotic stress (Ahmad 2010). Gibberellins regulate plant growth processes including seed germination stem extension, flowering and aging. Phytohormones and hormone-like compounds it can be ensure successful germination of seed or normal plant growth by controlling a symbiotic relationship between plant for example mycorrhizal fungi or nodule bacteria (Jaroszuk-Ściseł et al. 2014;Mefteh et al. 2017). Further most essential regulator gibberellins are necessary for plant production and development that had been play vital role in the development of lateral shoot growth, seed dormancy and the floral organs (Olszewski et al. 2002). There are several studies have also been documented we can improve germination and growth treated by the gibberellic acid under salt stress condition (Manjili et al. 2012;Tuna et al. 2008). According to Maggio et al. (2010) were treated tomato plants through the gibberellic acid under the saline condition where they have been observed that plant increased the crop growth and seed quantity. Gibberellic acid had been inducing most efficient absorption of iron within the plant system, leading to enhanced plant growth and the maintenance of plant metabolism under natural and stress condition (Iqbal and Ashraf 2013).
The endogenous application of GA resulted in alteration of plant osmotic stress and conservation of tissue water quality (Ahmad 2010). These results have been reported for wheat Manjili et al. (2012) and maize by Tuna et al. (2008). Furthermore, exogenous application of gibberellic acid mitigates the effects of salinity on germination and growth in Arabidopsis thaliana by mediating enhanced SA synthesis, which induces increased isochorismate synthase 1 activity (Alonso-Ramírez et al. 2009). Egamberdieva et al. (2017 reported that Arabidopsis improved salt tolerance gene and responsible for Fagus sylvatica they were producing gibberellins. Hasan (2002) recorded some fungi such as Rhizopus stolonifer, Pencillium funiculosum, P. cyclopium, P.
corylophilum, Fusarium oxysporum, Aspergillus niger and A. flavus where all of the fungal species are capable to produce gibberellins but Fusarium oxysporum were found to producing both of phytohormones like as indole-acetic acid (IAA) and gibberellins (GA).

Cytokinins
Cytokinin have been involved in numerous fundamental process including plant growth promotion, plant morphogenesis, metabolism, nutrient assimilation, cell differentiation, cell proliferation and the translocation maintenance that are performing some important role in symbiotic interaction (Boivin et al. 2016). Cytokinins (CK) an important group of plant hormones they are involved in sustaining cellular proliferation and differentiation and in preventing senescence, leading to inhibition of premature senescence in the leaf (Schmülling 2002). Chemically, the normal cytokinins are derivatives of purine substituted by N 6 . These are found mainly in plant like as zeatin, 6 benzylaminopurine and kinetin as well as these are also considered to play a vital role in integrating diverse response to environmental stress (Dervinis et al. 2010). Cytokinin Reduced contributes to ABA induced stomatal closure, thereby reducing carbon absorption and assimilation under the stressful condition and regulation of cytokinin oxidase may also reduce carbon metabolism; research on this topic may be fruitful in improving plant growth and yield. Mohapatra et al. (2011) have been proved that cytokinin enhance the filling of grains. Exogenous application of cytokinin is currently being used to improved cytokinin internal concentration.
Heavy metals such as lead and zinc have also been reported to seriously crate the growth of chickpea seedling in large quantity, they are inhibiting by GA3 and Z in plants (Atici et al. 2005). In earlier research we found out that chickpea of kinetin has stimulating the plant hormones under the salt stress condition with an additional cytokinin increasing its antioxidant efficiency and kinetin extenuate cadmium in to eggplants (Singh and Prasad 2014). It has been shown to have a beneficial effect on the roots of Arbuscular mycorrhizal fungi and they are responsible for the tobacco phosphate transporter gene of NtPT4 and then decreases the cytokinin content in root as well as they have been caused root growth depression of the Arbuscular mycorrhizal fungi of colonized plants (Cosme et al. 2016). This indicated that cytokinin are essential plant growth defence trading regulators and highlights the important of the finely balanced responses plants and the environments.

Ethylene
Ethylene is crucial phytohormones that have a broad range of biological activities that can influence plants growth promotion and development there are a wide variety of ways including promotion root initiation, root elongation, fruit maturation and activating other phytohormones (Glick et al. 2007). Ethylene is controlling the flowering of flowers, plant growth adaptation, ripening of fruits, root formation, senescence, seed germination and seed dormancy under the biotic and abiotic stress condition (Abeles et al. 2012;Kende 1993). The gaseous hormone is synthesized as precursors ACC, which derived from methionine and ACC oxidase and ACC synthase is a central enzyme in this biosynthetic pathway (Xu et al. 2018). Iqbal et al. (2012)published that improved fresh biomass, grain yield, nodule dry weight, nitrogen content of grains, nodule number and straw yield of lentil grain have been reported as a result of reduced ethylene production through promoting plant growth with inoculation strains with Pseudomonas sp. contains ACC deaminase, along with R. Leguminosa (Gupta et al. 2015).A gene that codes such as enzyme was not found in the genome of endophytic root-colonizing fungus Piriformospora indica. In the several studies Ethylene inhibits colonization of mycorrhizal fungi roots or rhizobacteria but there are also records of opposite effects (Khatabi and Schäfer 2012). Ansari et al. (2013) and Khatabi et al. (2012) synthesized Piriformospora indica strain of the fungus modulated through the ACC expression and ethylene were involving in ACC Arabidopsis.

Abscisic Acid
The abscisic acid phytohormones regulate many aspects of plant growth phytohormones and development of crop production including plant response various environmental stresses condition such as cold, desiccation and salinity (Finkelstein 2013). Abscisic acid is a typical stress hormone that is involved in so many osmotic reactions like as stress on salt and drought. Abscisic acid relevance to beneficial synergistic relationship has recently become an important area under study. Generally abscisic acid promotes Arbuscular mycorrhizal fungi symbiosis although the effect of the hormones is highly dependent on the developmental stage of the conditions of interaction and stress. López-Ráez (2016) and PeskanBerghöfer et al. (2015) showed that treatment of Arabidopsis seedling with exogenous ABA or ABA analog pyrabactim increased the efficiency of the fungal colonization without harm of plant fitness. Like other phytohormones ABA is play an important role in plant by enhancing responses and adaptation to stress. They are a naturally occurring sesquiterpenoid which is a group of main growth controlling phytohormones. The role of ABA in combining signalling with subsequent control of downstream responses during stress exposure has been confirmed by several studies (Wilkinson et al. 2012). The expression of stress-responsive gene had controlled by ABAinduced and mediated signalling under abiotic stress contributes to better elicitation of tolerance response (Sah et al. 2016). Additionally, under of drought stress condition, ABA was documented to regulate root growth and water content (Cutler et al. 2010).

Antibiotic productions
The term antibiotics covers wide range of chemical substances produced naturally, semi-synthetically and synthetically and used to inhibit (bacteriostatic) growth kill (bactericidal) bacteria (Gillings 2013;Martínez 2012;Milić et al. 2013). They are classifying as narrow or broad-spectrum antibiotics based on their effects as either bacteriostatic or bactericidal and on their series of effectiveness. In additional, the group of drug that are more broadly used in global level of the agriculture, that are increasing technical concern with regards to their possible adverse effects and risk reduction measures steps including the aminoglycosides, β-lactams, lincosamides, macrolides, pleuromutilins, sulphonamides and tetracyclines (Baynes et al. 2016;De Briyne et al. 2014;Finley et al. 2013).Fungi are very important to the soil ecosystem and play an incredible role in the everyday life of humans being as well as biofertilizers for the field of agriculture, bioremediation, natural regeneration and also used in food industries (Karthikeyan et al. 2014;Yadav and Yadav 2018). Additionally, fungi are also a significant source of secondary metabolites and ecologically, soil was considered abundant sources of antibiotic-producing microbes in the microbially reach environments due to strong competitions for nutrients and territory.
Over the 60 years ago the screening of the antibiotics was started with the organism of the soils and secondary metabolites contain high quantity from fungi were obtained from the soil for example production of secondary metabolites, antimicrobial agents, is one of the most significant uses of fungi that can potentially be useful for medical therapy (Al-Daamy et al. 2018;Farjana et al. 2014). These secondary metabolites are referred to as small organic molecules formed by organisms that are not required for their growth, development and also the reproduction; rather than they play an essential role against other living organisms in antagonism, competition and self-defence mechanism to enable the organism to occupy the niche and use the food. Fungi produced various antibiotics that exhibit antifungal and antibacterial activity, correspondingly that are broadly used as drugs worldwide, especially penicillin, cephalosporin, and fluidic acid (Al-Enazi et al. 2018). Additionally, endophytes of vascular plants have been the most widely explored ecological group in recent years (Karwehl and Stadler 2016). Novel antibacterial, anticancer, antifungal, anti-inflammatory, ant-malarial and antiviral substances have been reported to be produced by fungal endophytes (Higginbotham et al. 2013;Supaphon et al. 2018).
Antibiotics are commonly used products from agriculture and their functional amount is at least as high amount uses in humans. The calculation approximately that the extract amount of antibiotics used in global agriculture varies significantly as well as 50,000 tons per annum and theses antibiotics are mostly used in crop processing, animal husbandry and also used in aquaculture containing a similar chemical structure amid antibiotics used for human therapy. Antibiotics are used in a few parts of the worlds for the larger quantity in the animal husbandry apart used via humans. In crop production antibiotics uses is comparatively inferior to use in livestock. Specifically, the outspread use of antibiotics, they are free for all haphazard uses in agriculture, have threatened by the emergence of important pathogenic high level of antibiotics and /or antimicrobial resistance. Some human pathogens have evolved resistance stain (MRSA and VRE) to the commercial antibiotics that are difficult to treat some lifethreatening diseases that were previously thought to be safe. Some plants diseases are causing microbes have also developed resistance strain to important antibiotics like streptomycin and oxytetracycline (Sarkar et al. 2018

ACC (1-aminocyclopropane-1-carboxylate) deaminase activity
In the soil environment, a healthy plant faces both abiotic and biotic stress conditions that negatively affect the growth and development of the plants. The stress conditions include drought, flooding, heavy metal, salinity, low and high temperature (Nadeem et al. 2012) and the presence of pathogens. These stress conditions lead to certain physiological disorders in plants such as the nutritional and hormonal imbalance and increased production of ethylene (Sairam and Tyagi 2004). Ethylene is required by the plants for their normal growth and development and is also involved in the response of plants to various stresses (Glick 2014). The growth of the plant tissues, including flowers, fruits, leaves, roots, and stems, are affected by ethylene. The interaction of plants with mycorrhizal fungi involves ethylene (Gamalero et al. 2008). But the higher concentration of ethylene inhibits the elongation of the roots and nodulation in legumes, leads to defoliation, epinasty, leaf abscission, and leaf senescence (Yadav et al. 2020e).
Certain fungal genera help the plants to survive and grow under biotic and abiotic stress conditions by decreasing the inhibitory levels of ethylene with the help of 1-aminocyclopropane-1-carboxylate deaminase (ACCd) enzyme. ACCd is a pyridoxal phosphatedependent enzyme that breaks down the immediate precursor of ethylene i.e., ACC into ammonia and αketobutyrate (Singh et al. 2015) thereby reducing the harmful effects of ethylene. Trichoderma asperellum was evaluated for ACCd enzyme and fungal cultures grown with ACC as the sole nitrogen source showed high ACCd enzymatic activity (Viterbo et al. 2010

Hydrolytic enzymes production
Presently, enzymes are receiving considerable interest because of their applications in different fields including industries, like food, detergent, textiles, leather, pulp and paper and agriculture field. Fungi are known to produce certain type of enzymes like cellulose, laccase, pectinases and cellulase, which has been explained further.

Xylanases
Xylanase, an endo-β-1,4-xylanase is the hydrolytic enzyme that has necrotizing and enzymaticactivity that can trigger the plant immunity. This enzyme is glycoside hydrolase that catalyse the hydrolysis of β-1,4-xylan which is a structural polysaccharide abundantly presenting the primary cell wall of monocot plants. This enzyme also has an antagonist activity against various pathogens that inhibits plant growth (Tundo et al. 2020). Xylanase can be produced by the various fungal species like Aspergillus niger (Park et al. 2002)

Laccase
The enzyme laccases are the multi-copper monomeric glycoproteins which are widely distributed and have the potential to oxidize a broad spectrum of compounds of phenolic and non-phenolic. This enzyme is being used in industries like cosmetics, food, paper and pulp, pharmaceutical and textile. This enzyme is also used for the degradation of agricultural waste. Bacteria and fungi are known to produce this enzyme. Fungi are known to be the major producers and more than 60 fungal species belonging to Ascomycota, Basidiomycota, and Zygomycotawere reported (Kour et al. 2019b).

Pectinases
Pectinase refers to the group of enzymes that have an ability to catalyse pectin and pectic material by various pathways like de-esterification, hydrolysis and transelimination. This enzyme is widely used in the production of fruit juice and alcoholic beverages, poultry feed, textile product and paper, treatment of wastewater, extraction of vegetable oil, fermentation of tea and coffee (Tepe and Dursun 2014). This enzyme has also been reported for showing antagonist activity against pathogens.

Cellulase
Cellulase, a homopolymers of repeated units of cellobiose, which have the β1,4-glycosidic linkages that makes structural organization highly ordered and tightly packed is third largest enzyme that have been used worldwide for animal feed additives, cotton processing, detergent production, juice extraction and paper recycling. Nowadays, cellulase enzyme are known to have an agricultural application like plant growth promotion by the killing the pathogens. Cellulase kill pathogens by hydrolysing the cellulose-the major component of the cell wall of certain pathogens-by cleaving the internal bond of glycan chain and provide reducing or nonreducing ends of cellooligosaccharides for cellobiohydrolases (CBH; or exoglucanase, 1,4-β-Dglucan-cellobiohydrolase, EC 3.2.1.91) to attack. After that CBH hydrolyses chain ends and yieldcellobiose as the major product. At last, this cellobiose is hydrolysed by β-glucosidase into glucose and also releases glucose

Siderophores production
Iron is the fourth most abundant element in ground rock. Iron is the most essential micronutrients for the development of the plant and the plants involved in the most critical biological cycling, including chlorophyll biosynthesis, respiration and photosynthesis (Dixon and Kahn 2004;Kobayashi and Nishizawa 2012). Siderophores are produced a low molecular weight of compounds they can be utilized through the microorganism like bacteria and fungi as an iron (Fe) chelating agents. These compounds produce numerous kinds of microbes due to low iron solubility; they were responsible for iron deficiency and normally available in natural alkaline high pH soil(Sharma and Johri 2003). High ferrous ion (Fe 2+ ) concentration have been decreasing (Fe 3+ ) ions may lead to iron toxicity in anaerobic condition and the acidic soils, such as flooded soils, due to excessive iron absorption (Stein et al. 2009).
Which are responsible for the solubilization and transportation of this product into bacterial cells. Some bacteria produce siderophores of the hydroxamate form and others bacteria have been produce catecholate form (Ahmad et al. 2008). Microbes have evolved aggressively Fe taking strategies. The nutritional weakness of iron can be overcome by bacteria using chelator agents called siderophore. The siderophore producing microbes are able to bind and transport the iron-siderophore complex in a state of iron limitation through the expression of different proteins. The development of microbes' siderophore is beneficial to plants as it can inhibit the growth of plant pathogen. Siderophores have been involved in direct and indirect plant growth enhancement by microbial plant growth . While studying the typification of siderophores, it was found that Trichoderma harzianum reported with maxium hydroxymate and corboxylate production while T. asperellum, T. longibrachiatum, T. Virtue reported with lower hydroxymate and carboxylated content, as confirmed by the strength of colour. Ghosh et al. (2017) was identified three fungal species they were showing antagonistic activity against Trichoderma asperellum, T. harzianum, T. viride. Usha and Padmavathi (2013) was documented two fungal species Aspergillus flavus and A. niger that have been secreting less iron compound with secondary metabolites siderophore. In another study we were found plant growth-promoting fungi like as Trichoderma Asperella, Pochonia chlamydosporia, Purpureocillium lilacinum, Metarhizium anisopliae, Beauveria bassiana.Farias et al. (2018) were applied to crop of corn, sugarcane, soybean and tomato they were grown under two treatment conditions such as control without inoculation and inoculation with the fungal consortium. We have been identified and characterized siderophore-producing fungi that can be used as biofertilizers and biocontrol.

Fungi as plant growth promoters
In agriculture, fungi are gained significant popularity as a plant growth promoter. Mostly, various bacterial species have been studied and researched for enhancement of plants, but fungi are considered far superior. Fungi possess several characteristics features that bacteria do not pose like better ability over bacteria to tolerate harsh acidic conditions, mobilize nutrients like phosphorus, and produce phytohormones including IAA, gibberellins and siderophores (Kumar et al. 2018). The main mechanisms by which fungi enhance the growth of plants are nutrients acquisition and providing growth hormones.
Plants require various types of micro and macronutrients for their growth, which they absorb from the soil. But nowadays, available soil nutrients have been depleted due to conventional agriculture (over exploitation of chemical-based products), so, plants are not able to uptake the necessary requirements. Several types of chemical products for plants are available and being used by the farmers that have very deleterious effects on the environment as well as humans. So, fungi are the better alternative for nutrients acquisition. Fungi undergo mechanisms like solubilization that make available soluble forms of nutrients like phosphorus, potassium, zinc, and magnesium from the insoluble forms. Fungi also have an ability to produce low molecular weight siderophores that can use for the sequestration of iron (Kour et al. 2019b). The number of fungi has been reported for the acquisition of different nutrients like Azospririllium, Azotobacter, Azospirillum, Acetobacter and Rhizobium (Bahadur et al. 2016) reported for the potassium solubilization, Aureobasidium pullulans, Barnettozyma californica, Dothideomycetes sp., and Torulaspora sp. Was reported for the zinc solubilization (Fu et al. 2016).
Another potential of fungi that helps in the plant growth promotion is the biostimulation. Fungi produce of various phytohormones like auxin, cytokinin, gibberellins, abscisic acid and ethylene. These phytohormones are produces by plants also, but sometimes when conditions are not favourable production of phytohormones reduces that affects the plant growth. So, fungi have been reported for the production of phytohormones that enhances plant growth. Species like

Fungi as biological control agents
Pathogens affecting plant health are a major and chronic threat to food production and ecosystem stability worldwide (Compant et al. 2005). It has been estimated that about 10-16% of global food production is reduced due to field and post-harvest plant diseases (Lo Presti et al. 2015;Strange and Scott 2005). Since agriculture is the largest economic sector in the world so to ensure high yield pesticides including bactericides, fungicides, herbicides and insecticides are used. It has been estimated that more than two billion tons of pesticides are used every year all over the world to eliminate undesirable crop pests. But pesticides leave undesirable effects in the environment including the contamination of soil, groundwater and water bodies which then affect human and animal health due to their carcinogenic potential, recalcitrance, and toxicity (Baron et al. 2019).
Microbial diversification is one of the most important components of world biological diversity. Recent technologies utilized to study microbial diversity have found that a large proportion of microbes still remain undiscovered and further many of their ecological roles still remain unknown (Kumawat et al. 2019). Diverse groups of microbes have been known to play an important role in the agricultural sector such as biofertilizers enhancing the growth and productivity, maintaining soil health and fertility as well as biocontrol agents where they protect the plants against pathogens. Biocontrol is the use of beneficial organisms, their genes, and/or products, to lessen the negative impact of plant pathogens and promote positive responses by the plant (Vinale et al. 2008). Biological control of pests has been recognized as an alternative to the use of harmful pesticides. Though different groups of microbes have been reported with potential as biocontrol agents but fungi are most studied and applied (Schrank and Vainstein 2010).
The use of fungi as biocontrol agents is greatly beneficial due to their metabolic diversity and efficiency that enhances the chances of finding the apt isolates for biocontrol and their relative environmental safety, as they are primarily decomposers (Thomas and Read 2007 (Larran et al. 2016;Tranier et al. 2014). The use of fungi as biocontrol agents is a safe and ecofriendly strategy towards sustainable agriculture. Furthermore, hidden possibilities or uses of fungi could be explored to enhance agricultural productivity, nanoagriculture, and metabolite production (Singh et al. 2019).

Conclusion
The scientific community has been conscious for the past two and a half decades fungi play an important role in agriculture, medicine, ecology, biotechnology, and industries. They are also alternative approaches to exiting the enzymatic process these can be utilized in fermentation industries. Fungi are also having a multifarious role in plant growth promoting and make to environmentally safe. So, these fungi could utilize as biopesticides/biofertilizers in the field under stress conditions for plant growth and make to healthy. As a result, fungi are becoming more attractive in the situation of global must as novel sources of food, enzyme and antibiotics as well as secondary metabolites. In future work, fungi are needed still in many areas to be explored, including new innovation and crops. In the modern techniques of molecular biology, occupied proteomes, transcriptomes and metagenomes, can help to characterized and identified to find novel products for industrial growth. For future fungi research is hopeful, as a demand for pharmaceutical goods and agricultural products required.

Conflict of interest:
The authors have no conflicts of interest to declare. All co-authors have seen and agree with the contents of the manuscript.   Wang F, Tao J, Meng S et al. (2016a) A study of organic acid production in contrasts between two phosphate solubilizing fungi: Penicillium oxalicum and Aspergillus niger. Sci Rep 6:1-8 Li Z, Bai T, Dai L, Wang F, Tao J, Meng S et al. (2016b) A study of organic acid production in contrasts between two phosphate solubilizing fungi: