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1.1 Introduction

Arbuscular mycorrhizal (AM) fungi form symbiotic relationships with over 80 % of terrestrial plant species (Brundrett 2002). Arbuscular mycorrhizas are ancient and ubiquitous symbioses formed between a relatively small group of soil fungi and higher plant roots which has been traced back 460 million years (Redecker 2002). The symbiosis is primarily characterised by its association with phosphorus (P) uptake by host plants and the enhancement of water uptake through the extraradical fungal hyphal networks. This symbiosis can also trigger physiological and molecular signals at subcellular levels, alter plant community structure and increase plant tolerance to various abiotic and biotic stresses. Mycorrhizal hyphal networks link plants of the same and different species below ground and are able to transfer resources between plants and release signal molecule defence-related proteins, lipochitooligosaccharides and strigolactones. There have been significant recent advances in the understanding of physiological processes and taxonomy of these fungi (Kohout et al. 2014; Saito 2000). They are obligate symbionts belonging to the phylum Glomeromycota (Redecker et al. 2000). Their activity in agricultural ecosystems is well documented (Abbott and Gazey 1994; Bedini et al. 2013; Pellegrino and Bedini 2014) as is their presence during rehabilitation of forest ecosystems (Brundrett and Nanjappa 2013; Solaiman and Abbott 2003, 2008). The distribution of ectomycorrhizal (ECM) fungi is also widespread, but they form associations with only 3 % of terrestrial plant families (Smith and Read 2008). ECM fungi are members of the phyla Ascomycota and Basidiomycota (Hibbett et al. 2000; Siddiqui et al. 2008). Unlike the ECM fungi, AM fungi are dependent on plants for their carbon (C) and when a symbiosis is formed, both ECM and AM fungi can demand 20–40 % of photosynthetically fixed plant C (McNear 2013).

1.2 Molecular Identification and New Taxonomic Classification of AM Fungi

Molecular techniques are applied to the identification of AM fungi under both greenhouse and field conditions, but there are many limitations in relation to the detection methods used as these are multinuclear organisms (Kohout et al. 2014; Schüßler et al. 2001). The diversity of AM fungi identified using molecular techniques has been studied at an ecosystem level (Sanders et al. 1995), for particular plant species (Jansa et al. 2003; Kjøller and Rosendah 2001), during seasonal variation in colonisation of roots of arable crops (Daniell et al. 2001), for coexisting species (Gollotte et al. 2004; Vandenkoornhuyse et al. 2003), and in relation to the influence of agricultural practices (Brito et al. 2013).

Despite rapid advances in methodologies, molecular techniques are still considered difficult to use for the identification of AM fungi because DNA extraction from soils typically yields low quantity and quality compared to plant roots (Renker et al. 2003; Olsson et al. 2010). There are also methodological and biological challenges to accurately assess AM fungi community composition which arises from the vast differences in DNA quantity from spores and hyphae in soil used for template DNA (Schüßler et al. 2001). Moreover, the higher quantity of DNA in multi-nucleic AM fungal spores compared to hyphae which contain significantly fewer nuclei which can skew community composition data (Gamper et al. 2008). This leads to potential bias in estimates of relative abundance where AM fungal morphotypes during sporulation will have a greater relative abundance than other morphotypes (Saks et al. 2013). The recent progress of next-generation sequencing techniques will open up a detail examination of fungal communities, and the reduction of cost of analyses will lead to greater accessibility, but there will be challenges.

Kohout et al. (2014) recently used different primers to compare four routinely used AM fungal-specific primer systems for nuclear ribosomal DNA such as (1) the partial small subunit (SSU), (2) the partial large subunit (LSU), (3) the partial SSU and internal transcribed spacer (ITS; “Redecker”) and (4) the partial SSU-ITS-partial LSU region (“Krüger”). They also included a new primer combination (5) the ITS2 region in the comparison. They concluded that “Krüger” primers tended to yield the highest AM fungal diversity and higher Shannon diversity index than did SSU primers. They confirmed a strong bias towards the Glomeraceae in the LSU and SSU primer systems and differences in the composition of AM fungal communities based on the “Redecker” primer system.

Willis et al. (2013) considered aspects of AM fungal ecology emphasising past and present importance of the phylum and concluded that it is essential to include the AM symbiosis in studies of higher plants in order to provide a more holistic view of the ecosystems. Concomitant morphological and molecular analyses have led to major breakthroughs in the taxonomic organisation of the phylum Glomeromycota (Oehl et al. 2011). Fungi in this phylum are known to form arbuscular mycorrhizas, and so far the phylum has 3 classes, 5 orders, 14 families and 29 genera described. They present the current classification developed in several recent publications and provide a summary to facilitate the identification of taxa from genus to class level. The history and complexity of the taxonomy and systematics of these obligate biotrophs has been addressed by recognising four periods (Stürmer 2012). The initial discovery period (1845–1974) was categorised mainly by description of sporocarp-forming species and the proposal of a classification for these fungi. The following alpha taxonomy period (1975–1989) established a solid morphological basis for species identification and classification, resulting in report of many new species and the need to standardise the nomenclature of spore subcellular structures. The cladistics period (1990–2000) stated the first classification of AM fungi based only on phenotypic characters. At the end of this period, genetic characters played a role in defining taxa and elucidating evolutionary relationships within the group. The most recent phylogenetic fusion period (2001 to present) started with the proposal of a new classification based on genetic characters using sequences of the multicopy rRNA genes.

Opik et al. (2010) have offered a new database, MaarjAM, that summarises publicly available Glomeromycota DNA sequence and associated metadata. These data have been made accessible in an open-access database (http://maarjam.botany.ut.ee). Two hundred and eighty-two SSU rRNA gene virtual taxa were described based on a comprehensive phylogenetic analysis of all collated Glomeromycota sequences showing limited distribution ranges in most Glomeromycota taxa and a positive relationship between the width of a taxon’s geographical range and its host taxonomic range.

Based on morphological and molecular characteristics, 19 genera, viz. Acaulospora, Ambispora, Archaeospora, Cetraspora, Dentiscutata, Diversispora, Entrophospora, Fuscutata, Geosiphon, Gigaspora, Glomus, Intraspora, Kuklospora, Otospora, Pacispora, Paraglomus, Racocetra, Scutellospora and Quatunica, comprising more than 200 species are documented in AM fungi (Manoharachary et al. 2010). Liu et al. (2009) stated that the AM fungal taxonomy position has moved forward to a phylum with 214 species belonging to 19 genera, 13 families, 4 orders and 1 class now reported. It was suggested that molecular techniques would be the key approaches in the future study of AM fungal species diversity. However, the intraspecific diversity of Glomus mosseae in a survey of 186 publications reporting the occurrence of G. mosseae from at least 474 different sites from 55 countries resulted in a geographical map of their distribution based on both morphological and molecular techniques (Liu et al. 2009).

While the taxonomy of AM fungi is based on morphological characters of the asexual resting spores, molecular approaches to community ecology have revealed a previously unknown diversity from colonised roots (Rosendahl 2008). The long asexual evolution of the fungi has resulted in considerable genetic diversity within morphologically recognisable species which challenges concepts of individuals and populations. The fossil record and molecular data show that the evolutionary history of AM fungi goes back at least to the Ordovician (460 million years ago), coinciding with the colonisation of the terrestrial environment by the first land plants (Redecker 2002). The fast-growing number of available DNA sequences for molecular identification of the Glomales within roots has been designed and tested. These detection methods have opened up entirely new perspectives for studying the ecology of AM fungi.

The AM fungal phylogeny of the genus Glomus of the family Glomaceae has been analysed based on full-length SSU rRNA gene sequences and shows that Glomus is not monophyletic (Schwarzott et al. 2001). The separation of Archaeospora and Paraglomus from Glomus was reported. Two ancestral families of AM fungal species such as Archaeosporaceae and Paraglomaceae were discovered from deeply divergent ribosomal DNA sequences in the past (Morton and Redecker 2001). Each family is phylogenetically distant from each other and from other glomalean families despite similarities in mycorrhizal morphology. Morphological characters once considered unique clearly are distributed in phylogenetically distant groups. The spores of some species in Glomus have considerable divergence at the molecular level. It is the combination of DNA sequences and mycorrhizal morphology which provides the basis for recognising Archaeospora and Paraglomus. These investigations reinforce the value of molecular data sets in providing a clearer understanding of phylogeny which in turn can lead to a more robust taxonomy.

1.3 Mechanisms of Nutrient Exchange in Arbuscular Mycorrhizas

In AM associations, nutrient exchange between fungi and host is one of the most important functions. Recent advances in biochemical and molecular biological techniques have revealed a great amount of new information on this topic (Smith and Read 2008; Harrison 1999; Saito 2000; Smith and Smith 2012). This has largely reinforced the ideas concerning symbiotic C and P transfer proposed by classical works in the 1970s and 1980s (Tinker 1975). However, the biochemical mechanisms of nutrient exchange in this symbiosis are still unclear. The following view of phosphorus transfer from fungus to host plant has been widely accepted (Smith and Read 2008). Phosphate in the soil solution is absorbed in the extraradical hyphae via a P transporter (Harrison and van Buuren 1995). The absorbed P is condensed into polyphosphate (poly-P) in the extraradical hyphae and translocated by protoplasmic streaming into the intraradical hyphae (Cox et al. 1975; Cooper and Tinker 1981; Solaiman et al. 1999). At the end, the poly-P may be hydrolysed and released as P across the fungal membrane, probably at the arbuscule. Solaiman and Saito (2001) observed that a substantial proportion of P in mycorrhizal roots was of fungal origin, while the proportion of fungal biomass to root biomass was <2 %. Phosphate efflux and the decrease in poly-P content in the hyphae were both improved by the addition of glucose and 2-deoxyglucose, an analogue of glucose. The rates of enhancement for P efflux and poly-P decrease were analogous, suggesting that P efflux from intraradical hyphae was coupled with poly-P hydrolysis. Based on these findings, the translocation of P from fungus to host was estimated in relation to the distribution of hyphal P in extraradical and intraradical parts of the AM fungus (Solaiman and Saito 2001). By applying the technique of separating intraradical hyphae from host roots, they were able to clarify the translocation and transfer of P in AM symbiosis in a quantitative manner. Further investigation of P efflux using the present experimental system will shed light on the mechanisms of nutrient exchange.

AM fungi rely on the photosynthetic C supplied by their host plants to complete their life cycle. In return, the fungi supply nutrients to the plant especially P, N and Zn. The site of nutrients exchange is primarily the arbuscule (Solaiman and Saito 1997; Harrison 1999; Balestrini and Bonfante 2005). The molecular and structural organisations of arbuscules facilitate and regulate the processes of nutrient exchange. Plant N and P transporter proteins have been reported (Ellerbeck et al. 2013; Javot et al. 2007b). Gene expression studies also showed that specific members of these protein families are expressed in the roots of colonised plants (Harrison et al. 2002; Javot et al. 2007a). Phosphate acquisition via the mycorrhizal pathway begins with the uptake of available P from soil by fungal extraradical hyphae (Bucher 2007). These hyphae extend beyond the host root zone, allowing a greater soil volume to be exploited for P uptake. Uptake at the soil hypha interface is mediated by fungal high-affinity P transporters (Harrison and van Buuren 1995). Following fungal uptake, phosphate is transferred to the fungal vacuole where it is polymerised to form polyphosphate chains and translocated through the vacuolar compartment to the intraradical hyphae (Solaiman et al. 1999). The poly-P is then hydrolysed and phosphate released to the interfacial apoplast from where plant mycorrhizal Pht1 transporters guide the phosphate across the periarbuscular membrane for delivery to other parts of the plant. The extraradical hyphae of AM fungi also absorb ammonium, nitrate and amino acids (Hodge et al. 2001), and the role of mycorrhiza on N delivery is becoming better understood (Chalot et al. 2006; Ellerbeck et al. 2013). The majority of N is thought to be taken up in the form of ammonia via the fungal-encoded AMT1 family transporters such as the protein GintAMT1 characterised from Glomus intraradices (Lopez-Pedrosa et al. 2006). There is no evidence for fungal translocation of either ammonium or nitrate and it is thought that nitrogen transport occurs in the form of the amino acid arginine (Govindarajulu et al. 2005), and amino acids may be delivered directly to the interfacial apoplast for plant absorption. However, there is also evidence for an alternative route whereby arginine is broken down by ornithine aminotransferase and urease to release free ammonium. It has been proposed that ammonium is exported by protein-mediated mechanisms and a candidate fungal AMT transporter has been identified that is highly expressed in the internal hyphae (Govindarajulu et al. 2005). Gene expression analyses of medic and rice have identified mycorrhiza-induced transcripts that putatively encode ammonium transporters that are candidates for this function. There is also the possibility for passive ammonia uptake across the periarbuscular membrane, perhaps facilitated by the presence of aquaporin proteins (Uehlein et al. 2007). The use of radiolabeled substrates has demonstrated that AM fungi take up plant carbohydrates in the form of hexose (Solaiman and Saito 1997). The route of this transport is specific to the arbuscule. There is little molecular evidence for the presence of hexose export proteins in the periarbuscular membrane; although a number of mycorrhiza-responsive sugar transporter genes have been identified in medic, they are thought to act as proton-sugar symporters in sugar import rather than export, possibly in support of high metabolic activity in arbuscules (Harrison 1996).

AM fungi deliver both P and N to the root through arbuscules. Previously MtPT4, a Medicago truncatula phosphate transporter located in the periarbuscular membrane that is essential for symbiotic P transport and for maintenance, was identified (Javot et al. 2011). In mtpt4 mutants arbuscule degeneration occurs prematurely and symbiosis fails (Javot et al. 2011). The MtPT4 arbuscule phenotype is strongly correlated with shoot N levels. On the other, the transport mechanism of sugars to the apoplast is passive movement. For example, when hexose reached in the apoplast is absorbed by the fungus via specific transport proteins. The characterisation of the GpMST1 hexose transporter from Geosiphon pyriformis, a Glomeromycotan fungus, provides a promising direction for further investigation (Schussler et al. 2006). In the intraradical hyphae, much of the C is changed to storage lipids, predominantly as triacylglycerides. Lipids not only act as storage C but also are the main form of C translocated from intra- to extraradical hyphae where they provide the major respiratory substrate.

AM fungi provide benefits to their plant hosts by enhancing mineral nutrition, increasing tolerance to water stress, inducing greater resistance to pathogens and reduce sensitivity to toxic substances present in the soil. However, the cost of colonisation can be ~20 % of the host’s fixed C being consumed by the microbial symbiont. Nonetheless, under experimental conditions when nutrients are limiting, mycorrhizal crop plants typically exhibit a better performance over non-mycorrhizal plants in high-input agricultural systems, the relative advantages are reduced while the C costs remain same and the performance of colonised plants can fall below that of non-colonised plants (Janos 2007). Phillips et al. (2013) proposed a framework for considering how tree species and their mycorrhizal symbionts differentially couple C and nutrient cycles in temperate forests. Given that tree species predominantly colonise by a single type of AM fungi or ECM fungi and that the two types of fungi differ in their modes of nutrient acquisition, the abundance of AM and ECM trees in a paddock may provide an integrated index of biogeochemical transformations relevant to C cycling and nutrient retention.

AM fungi can obtain the photosynthates from host plants and can promote N uptake by host plants via the absorption of various N sources by mycorrhizal hyphae leading to improvement in nutrition and stress tolerance of host plants (Li et al. 2013). The symbiont absorbs and transfers N, but the mechanisms behind the N metabolism and translocation from AM fungi to host plants are still in debate. The roles of AM fungi in N allocation in host plants and the ecological significance at community and ecosystem levels need to be studied in more detail because they vary widely (Hodge and Storer 2014).

1.4 Role of AM Fungi in Sustainable Agriculture

Sustainable agricultural systems use natural processes to achieve satisfactory levels of productivity and food quality while decreasing fertiliser use, dropping input costs and preclude environmental pollution and its impacts (Siddiqui et al. 2008; Harrier and Watson 2004). It should also be ecologically feasible and socially responsible. Several soil factors contribute to sustainable agriculture through control of soil-borne diseases and increased soil microbial activity leading to increased antagonism and parasitism within the rhizosphere level (Jawson et al. 1993; Knudsen et al. 1995). Research approaches are presently focused on the search for suitable alternatives to the use of commercial artificial pesticides. However, progress has also been accomplished in exploring the use of microorganisms for improvement of soil fertility and ultimately increased crop productivity. Greater emphasis is being placed on enhancing exploitation of indigenous soil microbes which will contribute to soil fertility and increase plant growth as well as plant protection.

AM fungi have been difficult to study (Hamel and Strullu 2006), but they are now recognised as key components of soil ecosystems rather than only a plant root component. Recent advances in knowledge conveyed by new techniques for soil microbiology research open the way to AM fungi management in crop nutrition and production. AM fungi can influence crop growth, nutrition and production even in phosphorus-rich soils (Balzergue et al. 2013; Solaiman and Hirata 1997). However, growing crops in soil with lower levels of fertility could enhance the multiple beneficial effects of AM fungi in agroecosystem including decreased nutrient loss to the environment. Inclusion of mycorrhizal bioassays in soil testing protocol (Djuuna et al. 2009) for use in fertilisation recommendations and development of improved inoculants to manipulate AM fungi (Abbott et al. 1987) and screening of crop cultivars with improved symbiotic abilities (Smith et al. 1992) could contribute to agroecosystem stability and sustainability (Hamel and Strullu 2006).

In agriculture, several factors influence plant response and plant benefits from mycorrhizas such as host crop dependency on mycorrhizal colonisation, tillage, fertiliser application and the potential of mycorrhizal fungi inocula. Interest in AM fungal inoculation for sustainable agriculture is based on their roles in the improvement of plant growth through nutrient and water uptake (Augé 2004) and improvements in soil fertility as well as soil aggregate stability (Rillig et al. 2007; Rillig 2004).

1.5 Role of AM and ECM Fungi in Protection of Soil-Borne Diseases

Biological control of soil-borne diseases is currently accepted as a key practice in sustainable agriculture. AM fungi have shown potential in protecting host plants from soil-borne pathogens. While few AM isolates have been tested against these soil-borne pathogens, some appear to be more effective than others (Cameron et al. 2013; Azćon-Aguilar and Barea 1996). The degree of protection varies with the pathogen species involved and can be moderated by soil and other microclimatic conditions of the rhizosphere. Only weak responses to AM fungi colonisation have been found in some activities like lignification, production of phytoalexins and peroxidises and expression of genes encoding for PR proteins, indicating that AM fungi do not elicit typical defence responses (Azćon-Aguilar and Barea 1996). However, these compounds could make roots sensitive to the presence of pathogens and enhance defence mechanisms to subsequent pathogen infection (Benhamou et al. 1994). In this study, responses of AM and non-mycorrhizal transformed carrot roots to infection by Fusarium oxysporum f. sp. Chrysanthemi were investigated in mycorrhizal roots; the growth of the pathogen was usually restricted to the epidermis and cortical tissues, whereas in non-mycorrhizal roots the infection of pathogen reached at depth even up to the vascular stele. The Fusarium hyphae inside mycorrhizal roots exhibited a high level of structural disorganisation, probably induced by a strong reaction of the host cells characterised by the accumulation of phenolic-like compounds and the production of hydrolytic enzymes such as chitinases. This strong reaction was not induced by non-mycorrhizal roots, suggesting that the activation of plant defence responses by mycorrhiza formation provides a protection at a certain level against the pathogen. In contrast to the weak defence response towards AM fungi found in AM hosts, it is noteworthy that in myc− pea mutants, AM fungi trigger a strong resistance reaction. This suggests that the AM fungi are able to elicit a defence response but that symbiosis-specific genes have mechanism to control the expression of the genes related to plant defence during AM establishment (Gianinazzi-Pearson et al. 1996). The expression of several PRs in tobacco plants did not affect the level of colonisation by Glomus mosseae which was only reduced in plants constitutively expressing an acidic isoform of tobacco PR-2, a glucanase (Vierheilig et al. 1996).

Ectomycorrhizas (ECM) have a positive effect on the performance of seedlings due to the beneficial relationship between plants and mycorrhizal fungi (Guerin-Laguette et al. 2004; Machόn et al. 2006; Minchin et al. 2012). They are also effective against various plant root rot diseases (Duchesne 2000). Many studies have observed the protective role of ECM not only against fungal pathogens (Morin et al. 1999) but also against nematodes (Machόn et al. 2006). Pine wilt disease is a globally severe forest disease and demonstrates the importance of ECM relationships (Akema and Futai 2005). In this study, the abundant ECM found in the upper slope enhanced water uptake by the pines, mitigated drought stress and thereby decreased the mortality of pine trees from pine wilt disease.

1.6 Role of AM and ECM Fungi in Restoration of Native Forest Ecosystems

Land clearing of terrestrial ecosystems claims several million hectares annually in Australia (Warren et al. 1996) which causes loss of essential physicochemical and biological soil properties (Skujins and Allen 1986). These properties largely determine soil quality and fertility that supports plant establishment and productivity. Soil degradation limits the potential for restoration of native plants (Agnew and Warren 1996), and erosion and desertification are accelerated. Desertification reduces the inoculum potential of mutualistic symbionts such as AM fungi that are key ecological factors in governing the cycles of major plant nutrients and hence in sustaining vegetative covers in natural habitats.

AM fungi improve the ability of plants to establish and cope in stressful conditions including nutrient deficiency, drought and soil disturbance (Schreiner et al. 1997). The fungal hyphae contribute to the formation of water-stable aggregates necessary for good soil tilth (Jeffries and Barea 2000). Loss of mycorrhizal propagules from degraded ecosystems can overcome either by natural or artificial revegetation where an increase of inoculum may be needed in these ecosystems (Requena et al. 1996). Inoculation of plants with mycorrhizal fungi in revegetation schemes should not only help plant establishment (Herrera et al. 1993) but also improve soil biological, chemical and physical properties thus contributing to soil quality (Carrillo-García et al. 1999). The introduction of a plant species along with a known AM fungus is a successful biotechnological tool to aid the recovery of desertified ecosystems (Azćon-Aguilar et al. 2003).

Many forest trees are dependent on a symbiotic association of their roots with ECM fungi and mobilise minerals from soil and transfer them to the plant. In exchange the trees deliver assimilated C to the fungi. The hyphae of ECM fungi are the source of C to soil microbes and depend on their tree hosts for their energy needs. In return, they take up P, N, S and Zn from soil and translocate them to their host and greatly extend the functional root system of the host plants (Allen 1991). An ECM fungus can connect roots of several trees by fungal hyphae network. Most ECM fungi are basidiomycetes such as Amanita, Cortinarius, Lactarius, Russula and Suillus, among the best-known ECM genera (Hacskaylo 1972). ECM are widespread particularly in temperate regions where many of the ecologically important tree species involve such as species of Abies, Betula, Fagus, Picea, Pinus, Pseudotsuga, Quercus and Salix.

Below-ground biodiversity is essential for the maintenance of forest growth and ecosystem functions as well as for reforestation of disturbed lands due to mining activities. ECM fungi are economically symbiotic soil fungi forming a sheath around the root tip and form a special structure called Hartig net (Smith and Read 2008). They gain C from the tree and in return support the tree in taking up nutrients, water and metabolites. The fungus also protects plants from parasites, nematodes and soil pathogens. The importance of ECM in forest plantations has received much attention when it was observed that trees often fail to establish at new sites if the ECM symbiont was absent (Menkis et al. 2012). This effect has been found in exotic pine transplantation in different parts of the world. In Western Australia, Pinus radiata and P. pinaster failed to establish in nursery beds in the absence of ECM fungi (Lakhanpal 2000). Pine seedlings are known to be tolerant to environmental stresses such as acid mist when colonised with ECM fungi (Asai and Futai 2001). Tropical rainforests harbour the highest known tree diversity on the planet, and many ecological studies have attempted to explain the familiar symbiotic association of so many co-occurring species (Leigh et al. 2004; Valencia et al. 1994).

1.7 Conclusions

Mycorrhizal fungi are well known to have a wide range of benefits to their host plants. They can enhance nutrient uptake especially P, N and Zn. They can also suppress soil pathogens, enhance tolerance to drought stress and reduce sensitivity to toxic substances contaminated to the soil. The suitability of conditions needs to be managed for indigenous fungi to colonise hosts in their natural habitat or to minimise loss of these fungi with high-input farming/disturbance. Highly mycorrhizal host crop cultivars should be selected for use in crop rotations. Conventional plant breeding in soils with high nutrient contents may select against the most efficient fungal communities or even against the mycorrhizal association. Many efforts have been made in recent years to get benefits from mycorrhizas for agriculture, horticulture, forestry, land restoration and contaminated site remediation. The results have generally been consistently positive under controlled conditions, with some difficulties due to complications from diverse variables under field conditions. Mycorrhizal interactions between plants, fungi and the environment are complex and often indivisible. Mycorrhizas are an essential below-ground component in the establishment and sustainability of plant communities, but thorough knowledge is required to achieve maximum benefits from these microorganisms and their associations.