Analysis of Arbuscular Mycorrhizal Fungal Inoculant Benchmarks

Navigating nitrogen sustainability with microbiome-associated phenotypes

Crop microbiomes promote plant health through various mechanisms, including nutrient provisioning. However, agriculture neglected the importance of these microbiome-associated phenotypes (MAPs) in conventional management approaches originating from the Green Revolution. Green Revolution innovations, such as nitrogen fertilizers and high-yielding germplasm, supported an increase in global crop yields. Yet these advances also led to many environmental issues, including disruptions in microbially mediated nitrogen transformations that have reduced reliance on microbiomes for sustainable nitrogen acquisition. Overcoming the challenges introduced by the Green Revolution requires a shift toward ecologically informed agronomic strategies that incorporate MAPs into breeding and management decisions. Agriculture in the Anthropocene needs to mindfully manage crop microbiomes to decouple agrochemical inputs from profitable yields, minimizing the environmental repercussions of modern agriculture.

Morpho-physiological traits of soybean plants in symbiosis with Gigaspora sp. and submitted to water restriction

In agricultural production, periods in which there is a lack of water can affect the productivity of soybean crops. One alternative is the use of arbuscular mycorrhizal fungi (AMF), which maximize water absorption, biochemical regulation, leaf elasticity and transpiration, and water use regulation. The present study aimed to analyze the morphological and physiological traits of soybean plants associated with Gigaspora margarita and Gigaspora gigantea submitted to water restriction in nonsterilized soil. The soybean plants received 31 g of the AMF Gigaspora margarita or 46 g of Gigaspora gigantea separately at sowing and were cultivated in a greenhouse under natural light conditions with controlled relative humidity and temperature. Water restriction was imposed when the plants reached the V3 stage and were divided into three levels: irrigated (80%), moderate (60%), and severe (40%) field capacity (FC). The experimental design was completely randomized in a 3 × 3 factorial design (three inoculation treatments × three water restriction levels). Physiological and morphological parameters, photosynthetic pigments, electrolyte leakage, root colonization of soybean plants, and percentage of fungal spores were evaluated. The inoculation of Gigaspora gigantea promoted the adaptation of physiological (photosynthesis rate, transpiration, stomatal conductance, Ci/Ca ratio, and carboxylation) and morphological traits (plant height and stem diameter), with greater colonization of soybean roots under conditions of water restriction, and maximized the tolerance of plants to drought, mitigating the negative effects of these conditions regardless of the level of water restriction. Mycorrhizal inoculation promoted better functioning of the photosynthetic apparatus and growth of soybean plants.

Spatial and Temporal Variability Management for All Farmers: A Cell-Size Approach to Enhance Coffee Yields and Optimize Inputs

Coffee yield exhibits plant-level variability; however, due to operational issues, especially in smaller operations, the scouting and management of coffee yields are often hindered. Thus, a cell-size approach at the field level is proposed as a simple and efficient solution to overcome these constraints. This study aimed to present the feasibility of a cell-size approach to characterize spatio-temporal coffee production based on soil and plant attributes and yield (biennial effects) and to assess strategies for enhanced soil fertilization recommendations and economic results. The spatio-temporal study was conducted using a database composed of yield and soil and plant attributes from four harvest seasons of coffee plantation in the southeast region of Brazil. We used small plots as cells, where soil, leaf, and yield samples were taken, and the average value of each variable was assigned to each cell. The results indicated that macro- and micronutrient contents in the soil and leaves exhibited spatio-temporal heterogeneity between cells, suggesting that customized coffee tree management practices could be employed. The cell-size sampling strategy identified regions of varying yield over time and associated them with their biennial effect, enabling the identification of profitable areas to direct resource and input management in subsequent seasons. This approach optimized the recommendation of potassium and phosphate fertilizers on farms, demonstrating that localized management is feasible even with low spatial resolution. The cell-size approach proved to be adequate on two coffee farms and can be applied in scenarios with limited resources for high-density sampling, especially for small- and medium-sized farms.

Enhancing chickpea growth through arbuscular mycorrhizal fungus inoculation: facilitating nutrient uptake and shifting potential pathogenic fungal communities

Arbuscular mycorrhizal fungi (AMF) are the most widespread plant symbionts associated with plant roots, and theyperform numerous functions that contribute to plants' health and physiology. However, there are many knowledge gaps in how the interactions between AMF and root mycobiomes influence the performance of the host plants. To this end, we inoculated a local chickpea cultivar grown in agricultural soil under semi-controlled conditions with Rhizophagus irregularis. In addition to examining mycorrhizal colonization, plant biomass, and mineral nutrition, we sequenced the ITS region of the rDNA to assess the chickpea mycobiome and identify key fungal taxa potentially responding to R. irregularis inoculation. Our results showed that inoculation had a positive effect on chickpea biomass and mineral nutrition, especially the total aboveground phosphorus, potassium and sodium contents. Fusarium, Sporomia, Alternaria, and unknown Pleosporales were the most abundant taxa in the roots, while Stachybotris, Penicillum, Fusarium, Ascobolus, an unknown Pleosporales and Acrophialophora were the most abundant in the rhizosphere. Among the ASVs that either were enriched or depleted in the rhizosphere and roots are potential plant pathogens from the genera Didymella, Fusarium, Neocosmospora, and Stagonosporopsis. This study highlights the relevance of AMF inoculation not only for enhancing chickpea growth and mineral nutrition in semi-arid conditions but also for influencing the composition of the plants' fungal community which contributes to improved plant performance and resilience against biotic and abiotic stress.

Development of on-farm AMF inoculum production for sustainable agriculture in Senegal

The integration of endomycorrhizal fungi into agricultural practices as inoculum offers the potential to improve plant productivity while reducing reliance on expensive chemical fertilizers, which are not only economically costly but also detrimental to the environment. Mycorrhizal fungi play a crucial role in facilitating plant access to essential mineral elements (such as Phosphorus, Potassium, etc.) and water, particularly in soils characterized by arid and semi-arid conditions. where these resources are often limited. Despite the obvious advantages, the development of arbuscular mycorrhizal fungi (AMF) inoculum production in Africa is progressing on a small scale. This research aims to address this limitation by exploring the feasibility of producing mycorrhizal inoculum on a semi-industrial farm scale, achieved through the control and stabilization of production parameters. Crop residues as peanut shell, rice husk, sugar cane bagasse and millet ears were tested in Leonard jars and pots as alternatives to conventional sand production substrate for the multiplication of mycorrhizal fungi Glomus aggregatum IR27, Funneliformis mosseae, Rhizophagus irregulares and Glomus fasciculatum R10. Significant results were obtained on the peanut shell. Under mass production conditions in farm scale, Glomus aggregatum IR27 showed the best mycorization characteristics with 19.76% intensity and 88.93% frequencies. The study highlighted the critical considerations of irrigation water salt content and substrate sterilization as essential parameters to ensure optimal development of mycorrhizal propagules. Water containing 0.5% salt inhibited the mycorrhization. This negative effect of salt was much more accentuated in unsterilized peanut shell substrate than in sterilized one. This experimental study constitutes a pioneering initiative, potentially replicable in other agricultural areas. Its sustainability is based on the simplicity and efficiency of the technology, which opens the prospect of increasing the number of AMF inoculum production units on a national scale in Senegal.

The composition of the arbuscular mycorrhizal fungal bacteriome is species dependent

BACKGROUND

In addition to their role as endosymbionts for plant roots, arbuscular mycorrhizal fungi (AMF) engage in complex interactions with various soil microorganisms, the rhizosphere, and the root endosphere of host plants. They also host diverse prokaryotic groups within their mycelia, contributing to what is termed multipartite symbiosis. In this study, we examined the impact of three AMF species-Rhizophagus irregularis, R. clarus, and R. cerebriforme-combined with microbial bioaugmentation on the diversity and composition of bacterial communities in the mycelia and hyphosphere. Using a microcosm design to separate the influence of host plant roots from AMF mycelia and Illumina MiSeq amplicon sequencing to analyze the bacterial communities.

RESULTS

Our results revealed that, while AMF identity and microbial bioaugmentation did not affect the structure of bacterial communities in the hyphosphere soil, they significantly altered the communities associated with their mycelia. Although all three AMF species belong to the same genus, with R. irregularis and R. clarus being closely related compared to R. cerebriforme, we observed variations in the bacterial communities associated with their mycelia. Interestingly, the mycelial bacterial community of R. cerebriforme contained 60 bacteriome core taxa exclusive to it, while R. clarus and R. irregularis had 25 and 9 exclusive taxa, respectively.

CONCLUSION

This study suggests that organismal phylogeny influences the bacterial communities associated with AMF mycelia. These findings provide new insights into AMF and bacterial interactions, which are crucial for the successful deployment of AMF inoculants. The taxonomic diversity of AMF inoculants is important for engineering the plant microbiome and enhancing ecosystem services.

Native Arbuscular Mycorrhizal Fungi Promote Plukenetia volubilis Growth and Decrease the Infection Levels of Meloidogyne incognita

The use of arbuscular mycorrhizal fungi (AMF) offers promising benefits to agriculture in the Amazon regions, where soils are characteristically acidic and nutrient-poor. The purpose of this research was to investigate the potential effects of two recently described species of AMF (Nanoglomus plukenetiae and Rhizoglomus variabile) native to the Peruvian Amazon for improving the plant growth of Plukenetia volubilis (inka nut or sacha inchi) and protecting the roots against soil pathogens. Two assays were simultaneously conducted under greenhouse conditions in Peru. The first focused on evaluating the biofertilizer effect of AMF inoculation, while the second examined the bioprotective effect against the root knot nematode, Meloidogyne incognita. Overall, the results showed that AMF inoculation of P. volubilis seedlings positively improved their development, particularly their biomass, height, and the leaf nutrient contents. When seedlings were exposed to M. incognita, plant growth was also noticeably higher for AMF-inoculated plants than those without AMF inoculation. Nematode reproduction was significantly suppressed by the presence of AMF, in particular R. variabile, and especially when inoculated prior to nematode exposure. The dual AMF inoculation did not necessarily lead to improved crop growth but notably improved P and K leaf contents. The findings provide strong justification for the development of products based on AMF as agro-inputs to catalyze nutrient use and uptake and protect crops against pests and diseases, especially those that are locally adapted to local crops and cropping conditions.

Arbuscular Mycorrhizal Fungi as Biostimulant and Biocontrol Agents: A Review

Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing more sustainable agriculture, reducing the use of chemical inputs is becoming a major concern. After providing an overview on AMF history, phylogeny, development cycle and symbiosis benefits, the current review aims to explore the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as a promising tool in the biocontrol market, as an alternative to chemical phytosanitary products, is underexplored and underdiscussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcome.

Exploring the diversity and potential functional characteristics of microbiota associated with different compartments of Schisandra chinensis

Introduction

Symbiotic microbial have a significant impact on the growth and metabolism of medicinal plants. Schisandra chinensis is a very functionally rich medicinal herb; however, its microbial composition and diversity have been poorly studied.

Methods

In the present study, the core microbiomes associated with the rhizospheric soil, roots, stems, leaves, and fruits of S. chinensis from six geographic locations were analyzed by a macro-genomics approach.

Results

Alpha and beta diversity analyses showed that the diversity of microbial composition of S. chinensis fruits did not differ significantly among the geographic locations as compared to that in different plant compartments. Principal coordinate analysis showed that the microbial communities of S. chinensis fruits from the different ecological locations were both similar and independent. In all S. chinensis samples, Proteobacteria was the most dominant bacterial phylum, and Ascomycota and Basidiomycota were the most dominant fungal phyla. Nitrospira, Bradyrhizobium, Sphingomonas, and Pseudomonas were the marker bacterial populations in rhizospheric soils, roots, stems and leaves, and fruits, respectively, and Penicillium, Golubevia, and Cladosporium were the marker fungal populations in the rhizospheric soil and roots, stems and leaves, and fruits, respectively. Functional analyses showed a high abundance of the microbiota mainly in biosynthesis.

Discussion

The present study determined the fungal structure of the symbiotic microbiome of S. chinensis, which is crucial for improving the yield and quality of S. chinensis.

Fungi beyond limits: The agricultural promise of extremophiles

Global climate changes threaten food security, necessitating urgent measures to enhance agricultural productivity and expand it into areas less for agronomy. This challenge is crucial in achieving Sustainable Development Goal 2 (Zero Hunger). Plant growth-promoting microorganisms (PGPM), bacteria and fungi, emerge as a promising solution to mitigate the impact of climate extremes on agriculture. The concept of the plant holobiont, encompassing the plant host and its symbiotic microbiota, underscores the intricate relationships with a diverse microbial community. PGPM, residing in the rhizosphere, phyllosphere, and endosphere, play vital roles in nutrient solubilization, nitrogen fixation, and biocontrol of pathogens. Novel ecological functions, including epigenetic modifications and suppression of virulence genes, extend our understanding of PGPM strategies. The diverse roles of PGPM as biofertilizers, biocontrollers, biomodulators, and more contribute to sustainable agriculture and environmental resilience. Despite fungi's remarkable plant growth-promoting functions, their potential is often overshadowed compared to bacteria. Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbiosis with many terrestrial plants, enhancing plant nutrition, growth, and stress resistance. Other fungi, including filamentous, yeasts, and polymorphic, from endophytic, to saprophytic, offer unique attributes such as ubiquity, morphology, and endurance in harsh environments, positioning them as exceptional plant growth-promoting fungi (PGPF). Crops frequently face abiotic stresses like salinity, drought, high UV doses and extreme temperatures. Some extremotolerant fungi, including strains from genera like Trichoderma, Penicillium, Fusarium, and others, have been studied for their beneficial interactions with plants. Presented examples of their capabilities in alleviating salinity, drought, and other stresses underscore their potential applications in agriculture. In this context, extremotolerant and extremophilic fungi populating extreme natural environments are muchless investigated. They represent both new challenges and opportunities. As the global climate evolves, understanding and harnessing the intricate mechanisms of fungal-plant interactions, especially in extreme environments, is paramount for developing effective and safe plant probiotics and using fungi as biocontrollers against phytopathogens. Thorough assessments, comprehensive methodologies, and a cautious approach are crucial for leveraging the benefits of extremophilic fungi in the changing landscape of global agriculture, ensuring food security in the face of climate challenges.

Diversity, Distribution, and applications of arbuscular mycorrhizal fungi in the Arabian Peninsula

Investigations of arbuscular mycorrhizal fungi (AMF) received extreme interests among scientist including agronomists and environmental scientists. This interest is linked to advantages provided by AMF in enhancing the nutrients of their hosts via improving photosynthetic pigments and antioxidant production. Further, it also positively alters the production of plant hormones. AMF through its associations with plants obtain carbon while in exchange, provide nutrients. AMF have been reported to improve the growth of Tageteserecta, Zea mays, Panicum turgidum, Arachis hypogaea, Triticum aestivum and others. This review further documented the occurrence, diversity, distribution, and agricultural applications of AMF species reported in the Arabian Peninsula. Overall, we documented 20 genera and 61 species of Glomeromycota in the Arabian Peninsula representing 46.51 % of genera and 17.88 % of species of AMF known so far. Funneliformis mosseae has found to be the most widely distributed species followed by Claroideoglomus etuicatum. There are 35 research articles focused on Arabian Peninsula where the stress conditions like drought, salinity and pollutants are prevailed. Only one group studied the influence of AMF on disease resistance, while salinity, drought, and cadmium stresses were investigated in 18, 6, and 4 investigations, respectively. The genus Glomus was the focus of most studies. The conducted research in the Arabian Peninsula is not enough to understand AMF taxonomy and their functional role in plant growth. Expanding the scope of detection of AMF, especially in coastal areas is essential. Future studies on biodiversity of AMF are essential.

Optimizing factors for large-scale production of Arbuscular Mycorrhizal Fungi consortia using root organ cultures

Large-scale production of Arbuscular Mycorrhizal Fungi (AMF) consortia is a crucial stride in harnessing their potential for sustainable agriculture and plant growth enhancement. However, establishing optimal production conditions is challenging due to their obligate nature, variability, lack of standardized protocols, and limited understanding of their specific requirements. Previous attempts to standardize Root Organ Cultures (ROC) for AMF overlooked challenges related to viable inoculum production for field applications. This current investigation reported, for the first time, the optimization of various factors during large-scale production of AMF using ROC. By optimizing factors like gelling agents, media preparation, medium-to-inoculum ratios, incubation conditions, age, harvesting method and drying temperatures, we achieved significant yields of viable propagules. The standardized protocol outlined in this study will greatly influence commercial-scale AMF production. These standardized protocols are poised to contribute to larger-scale AMF production worldwide, with the potential to support sustainable agriculture and ecosystem management.

Comparative RNA sequencing-based transcriptome profiling of ten grapevine rootstocks: shared and specific sets of genes respond to mycorrhizal symbiosis

Arbuscular mycorrhizal symbiosis improves water and nutrient uptake by plants and provides them other ecosystem services. Grapevine is one of the major crops in the world. Vitis vinifera scions generally are grafted onto a variety of rootstocks that confer different levels of resistance against different pests, tolerance to environmental stress, and influence the physiology of the scions. Arbuscular mycorrhizal fungi are involved in the root architecture and in the immune response to soil-borne pathogens. However, the fine-tuned regulation and the transcriptomic plasticity of rootstocks in response to mycorrhization are still unknown. We compared the responses of 10 different grapevine rootstocks to arbuscular mycorrhizal symbiosis (AMS) formed with Rhizophagus irregularis DAOM197198 using RNA sequencing-based transcriptome profiling. We have highlighted a few shared regulation mechanisms, but also specific rootstock responses to R. irregularis colonization. A set of 353 genes was regulated by AMS in all ten rootstocks. We also compared the expression level of this set of genes to more than 2000 transcriptome profiles from various grapevine varieties and tissues to identify a class of transcripts related to mycorrhizal associations in these 10 rootstocks. Then, we compared the response of the 351 genes upregulated by mycorrhiza in grapevine to their Medicago truncatula homologs in response to mycorrhizal colonization based on available transcriptomic studies. More than 97% of the 351 M. truncatula-homologous grapevine genes were expressed in at least one mycorrhizal transcriptomic study, and 64% in every single RNAseq dataset. At the intra-specific level, we described, for the first time, shared and specific grapevine rootstock genes in response to R. irregularis symbiosis. At the inter-specific level, we defined a shared subset of mycorrhiza-responsive genes.

Arbuscular mycorrhizal fungi as biofertilisers

Salvioli di Fossalunga and Bonfante introduce how arbuscular mycorrhizal fungi can be applied as biofertilizers.

Disentangling arbuscular mycorrhizal fungi and bacteria at the soil-root interface

Arbuscular mycorrhizal fungi (AMF) are essential components of the plant root mycobiome and are found in approximately 80% of land plants. As obligate plant symbionts, AMF harbor their own microbiota, both inside and outside the plant root system. AMF-associated bacteria (AAB) possess various functional traits, including nitrogen fixation, organic and inorganic phosphate mobilization, growth hormone production, biofilm production, enzymatic capabilities, and biocontrol against pathogen attacks, which not only contribute to the health of the arbuscular mycorrhizal symbiosis but also promote plant growth. Because of this, there is increasing interest in the diversity, functioning, and mechanisms that underlie the complex interactions between AMF, AAB, and plant hosts. This review critically examines AMF-associated bacteria, focusing on AAB diversity, the factors driving richness and community composition of these bacteria across various ecosystems, along with the physical, chemical, and biological connections that enable AMF to select and recruit beneficial bacterial symbionts on and within their structures and hyphospheres. Additionally, potential applications of these bacteria in agriculture are discussed, emphasizing the potential importance of AMF fungal highways in engineering plant rhizosphere and endophyte bacteria communities, and the importance of a functional core of AAB taxa as a promising tool to improve plant and soil productivity. Thus, AMF and their highly diverse bacterial taxa represent important tools that could be efficiently explored in sustainable agriculture, carbon sequestration, and reduction of greenhouse gas emissions related to nitrogen fertilizer applications. Nevertheless, future studies adopting integrated multidisciplinary approaches are crucial to better understand AAB functional diversity and the mechanisms that govern these tripartite relationships.

Microbial-Based Plant Biostimulants

Beneficial microorganisms offer essential ecological services to both natural and agricultural ecosystems [...].

The Potential Applications of Commercial Arbuscular Mycorrhizal Fungal Inoculants and Their Ecological Consequences

Arbuscular mycorrhizal fungal (AMF) inoculants are sustainable biological materials that can provide several benefits to plants, especially in disturbed agroecosystems and in the context of phytomanagement interventions. However, it is difficult to predict the effectiveness of AMF inoculants and their impacts on indigenous AMF communities under field conditions. In this review, we examined the literature on the possible outcomes following the introduction of AMF-based inoculants in the field, including their establishment in soil and plant roots, persistence, and effects on the indigenous AMF community. Most studies indicate that introduced AMF can persist in the target field from a few months to several years but with declining abundance (60%) or complete exclusion (30%). Further analysis shows that AMF inoculation exerts both positive and negative impacts on native AMF species, including suppression (33%), stimulation (38%), exclusion (19%), and neutral impacts (10% of examined cases). The factors influencing the ecological fates of AMF inoculants, such as the inherent properties of the inoculum, dosage and frequency of inoculation, and soil physical and biological factors, are further discussed. While it is important to monitor the success and downstream impacts of commercial inoculants in the field, the sampling method and the molecular tools employed to resolve and quantify AMF taxa need to be improved and standardized to eliminate bias towards certain AMF strains and reduce discrepancies among studies. Lastly, inoculant producers must focus on selecting strains with a higher chance of success in the field, and having little or negligible downstream impacts.

Effects of Commercial Arbuscular Mycorrhizal Inoculants on Plant Productivity and Intra-Radical Colonization in Native Grassland: Unintentional De-Coupling of a Symbiosis?

There has been a surge in industries built on the production of arbuscular mycorrhizal (AM) fungal-based inoculants in the past few decades. This is not surprising, given the positive effects of AM fungi on plant growth and nutritional status. However, there is growing concern regarding the quality and efficacy of commercial inoculants. To assess the potential benefits and negative consequences of commercial AM fungal inoculants in grasslands, we conducted a controlled growth chamber study assessing the productivity and AM fungal root colonization of nine grassland plant species grown in grassland soil with or without one of six commercial AM fungal products. Our research showed no evidence of benefit; commercial inoculants never increased native plant biomass, although several inoculants decreased the growth of native species and increased the growth of invasive plant species. In addition, two commercial products contained excessive levels of phosphorus or nitrogen and consistently reduced AM fungal root colonization, indicating an unintentional de-coupling of the symbiosis. As there is little knowledge of the ecological consequences of inoculation with commercial AM fungal products, it is critical for restoration practitioners, scientists, and native plant growers to assess the presence of local AM fungal communities before investing in unnecessary, or possibly detrimental, AM fungal products.

Experimental evaluation of biological regeneration of arable soil: The effects of grass-clover leys and arbuscular mycorrhizal inoculants on wheat growth, yield, and shoot pathology

Wheat yields have plateaued in the UK over the last 25 years, during which time most arable land has been annually cropped continuously with short rotations dominated by cereals. Arable intensification has depleted soil organic matter and biology, including mycorrhizas, which are affected by tillage, herbicides, and crop genotype. Here, we test whether winter wheat yields, mycorrhization, and shoot health can be improved simply by adopting less intensive tillage and adding commercial mycorrhizal inoculum to long-term arable fields, or if 3-year grass-clover leys followed direct drilling is more effective for biological regeneration of soil with reduced N fertiliser. We report a trial of mycorrhization, ear pathology, and yield performance of the parents and four double haploid lines from the Avalon x Cadenza winter wheat population in a long-term arable field that is divided into replicated treatment plots. These plots comprised wheat lines grown using ploughing or disc cultivation for 3 years, half of which received annual additions of commercial arbuscular mycorrhizal (AM) inoculum, compared to 3-year mown grass-clover ley plots treated with glyphosate and direct-drilled. All plots annually received 35 kg of N ha^-1 fertiliser without fungicides. The wheat lines did not differ in mycorrhization, which averaged only 34% and 40% of root length colonised (RLC) in the ploughed and disc-cultivated plots, respectively, and decreased with inoculation. In the ley, RLC increased to 52%. Two wheat lines were very susceptible to a sooty ear mould, which was lowest in the ley, and highest with disc cultivation. AM inoculation reduced ear infections by >50% in the susceptible lines. In the ley, yields ranged from 7.2 to 8.3 t ha^-1, achieving 92 to 106% of UK average wheat yield in 2018 (7.8 t ha^-1) but using only 25% of average N fertiliser. Yields with ploughing and disc cultivation averaged only 3.9 and 3.4 t ha^-1, respectively, with AM inoculum reducing yields from 4.3 to 3.5 t ha^-1 in ploughed plots, with no effect of disc cultivation. The findings reveal multiple benefits of reintegrating legume-rich leys into arable rotations as part of a strategy to regenerate soil quality and wheat crop health, reduce dependence on nitrogen fertilisers, enhance mycorrhization, and achieve good yields.

Establishing a quality management framework for commercial inoculants containing arbuscular mycorrhizal fungi

Microbial inoculants containing arbuscular mycorrhizal (AM) fungi are potential tools in increasing the sustainability of our food production systems. Given the demand for sustainable agriculture, the production of such inoculants has potential economic value and has resulted in a variety of commercial inoculants currently being advertised. However, their use is limited by inconsistent product efficacy and lack of consumer confidence. Here, we propose a framework that can be used to assess the quality and reliability of AM inoculants. First, we set out a range of basic quality criteria which are required to achieve reliable inoculants. This is followed by a standardized bioassay which can be used to test inoculum viability and efficacy under controlled conditions. Implementation of these measurements would contribute to the adoption of AM inoculants by producers with the potential to increase sustainability in food production systems.

The effects of arbuscular mycorrhizal fungal species and taxonomic groups on stressed and unstressed plants: a global meta-analysis

The great majority of plants gain access to soil nutrients and enhance their performance under stressful conditions through symbiosis with arbuscular mycorrhizal fungi (AMF). The benefits that AMF confer vary among species and taxonomic groups. However, a comparative analysis of the different benefits among AMF has not yet been performed. We conducted a global meta-analysis of recent studies testing the benefits of individual AMF species and main taxonomic groups in terms of plant performance (growth and nutrition). Separately, we examined AMF benefits to plants facing biotic (pathogens, parasites, and herbivores) and abiotic (drought, salinity, and heavy metals) stress. AMF had stronger positive effects on phosphorus nutrition than on plant growth and nitrogen nutrition and the effects on the growth of plants facing biotic and abiotic stresses were similarly positive. While the AMF taxonomic groups showed positive effects on plant performance either with or without stress, Diversisporales were the most beneficial to plants without stress and Gigasporales to plants facing biotic stress. Our results provide a comprehensive analysis of the benefits of different AMF species and taxonomic groups on plant performance and useful insights for their management and use as bio-inoculants for agriculture and restoration.

Arbuscular Mycorrhizal Fungi Symbiosis to Enhance Plant–Soil Interaction

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with plants; a symbiotic relationship is one in which both partners benefit from each other. Fungi benefit plants by improving uptake of water and nutrients, especially phosphorous, while plants provide 10–20% of their photosynthates to fungus. AMF tend to make associations with 85% of plant families and play a significant role in the sustainability of an ecosystem. Plants’ growth and productivity are negatively affected by various biotic and abiotic stresses. AMF proved to enhance plants’ tolerance against various stresses, such as drought, salinity, high temperature, and heavy metals. There are some obstacles impeding the beneficial formation of AMF communities, such as heavy tillage practices, high fertilizer rates, unchecked pesticide application, and monocultures. Keeping in view the stress-extenuation potential of AMF, the present review sheds light on their role in reducing erosion, nutrient leaching, and tolerance to abiotic stresses. In addition, recent advances in commercial production of AMF are discussed.

The Metabolic Profile of Anchusa officinalis L. Differs According to Its Associated Arbuscular Mycorrhizal Fungi

Anchusa officinalis (L.) interacts with various microorganisms including arbuscular mycorrhizal fungi (AMF). Recently, the AMF Rhizophagus irregularis MUCL 41833 has been shown to modulate the metabolome of A. officinalis. However, little information is available on the impact that different AMF species may have on primary and secondary plant metabolites. In this study, four AMF species belonging to the genus Rhizophagus (R. irregularis MUCL 41833, R. intraradices MUCL 49410, R. clarus MUCL 46238, R. aggregatus MUCL 49408), were evaluated for their potential to modulate A. officinalis metabolome under controlled semi-hydroponic cultivation conditions. An untargeted metabolomic analysis was performed using UHPLC-HRMS followed by a multivariate data analysis. Forty-two compounds were reported to be highly modulated in relation to the different AMF associations. Among them, six new secondary metabolites were tentatively identified including two acetyl- and four malonyl- phenylpropanoid and saponin derivatives, all presenting a common substitution at position C-6 of the glycosidic moiety. In addition, an enhanced accumulation of primary and secondary metabolites was observed for R. irregularis and R. intraradices, showing a stronger effect on A. officinalis metabolome compared to R. clarus and R. aggregatus. Therefore, our data suggest that different AMF species may specifically modulate A. officinalis metabolite production.

Influence on Soybean Aphid by the Tripartite Interaction between Soybean, a Rhizobium Bacterium, and an Arbuscular Mycorrhizal Fungus

The inoculation of arbuscular mycorrhizal (AM) fungi and rhizobia in legumes has been proven to increase plant growth and yield. To date, studies of the effects of these interactions on phytophagous insects have shown them to be context-dependent depending on the inoculant strain, the plant, and the insect species. Here, we document how a symbiosis involving an AM fungus, Rhizophagus irregularis; a rhizobium, Bradyrhizobium japonicum; and soybean, Glycine max, influences the soybean aphid, Aphis glycines. Soybean co-inoculated with the AM fungus–rhizobium pair increased the plant’s biomass, nodulation, mycorrhizal colonization, nitrogen, and carbon concentrations, but decreased phosphorus concentration. Similar effects were observed with rhizobium alone, with the exception that root biomass was unaffected. With AM fungus alone, we only observed an increase in mycorrhizal colonization and phosphorus concentration. The aphids experienced an increased reproductive rate with the double inoculation, followed by rhizobium alone, whereas no effect was observed with the AM fungus. The size of individual aphids was not affected. Furthermore, we found positive correlation between nitrogen concentration and aphid population density. Our results confirm that co-inoculation of two symbionts can enhance both plant and phytophagous insect performance beyond what either symbiont can contribute alone.

Plant-Mycorrhizal Fungi Interactions in Phytoremediation of Geogenic Contaminated Soils

Soil contamination by geogenic contaminants (GCs) represents an imperative environmental problem. Various soil remediation methods have been successfully employed to ameliorate the health risks associated with GCs. Phytoremediation is considered as an eco-friendly and economical approach to revegetate GC-contaminated soils. However, it is a very slow process, as plants take a considerable amount of time to gain biomass. Also, the process is limited only to the depth and surface area of the root. Inoculation of arbuscular mycorrhizal fungi (AMF) with remediating plants has been found to accelerate the phytoremediation process by enhancing plant biomass and their metal accumulation potential while improving the soil physicochemical and biological characteristics. Progress in the field application is hindered by a lack of understanding of complex interactions between host plant and AMF that contribute to metal detoxification/(im)mobilization/accumulation/translocation. Thus, this review is an attempt to reveal the underlying mechanisms of plant-AMF interactions in phytoremediation.

Diversity of Phosphate Chemical Forms in Soils and Their Contributions on Soil Microbial Community Structure Changes

In many soils, the bioavailability of Phosphorus (P), an essential macronutrient is a limiting factor for crop production. Among the mechanisms developed to facilitate the absorption of phosphorus, the plant, as a holobiont, can rely on its rhizospheric microbial partners. Therefore, microbial P-solubilizing inoculants are proposed to improve soil P fertility in agriculture. However, a better understanding of the interactions of the soil-plant-microorganism continuum with the phosphorus cycle is needed to propose efficient inoculants. Before proposing further methods of research, we carried out a critical review of the literature in two parts. First, we focused on the diversity of P-chemical forms. After a review of P forms in soils, we describe multiple factors that shape these forms in soil and their turnover. Second, we provide an analysis of P as a driver of microbial community diversity in soil. Even if no rule enabling to explain the changes in the composition of microbial communities according to phosphorus has been shown, this element has been perfectly targeted as linked to the presence/absence and/or abundance of particular bacterial taxa. In conclusion, we point out the need to link soil phosphorus chemistry with soil microbiology in order to understand the variations in the composition of microbial communities as a function of P bioavailability. This knowledge will make it possible to propose advanced microbial-based inoculant engineering for the improvement of bioavailable P for plants in sustainable agriculture.

Long-Term Persistence of Arbuscular Mycorrhizal Fungi in the Rhizosphere and Bulk Soils of Non-host Brassica napus and Their Networks of Co-occurring Microbes

Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that improve the nutrition and health of their host. Most, but not all the crops form a symbiosis with AMF. It is the case for canola (Brassica napus), an important crop in the Canadian Prairies that is known to not form this association. From 2008 to 2018, an experiment was replicated at three locations of the Canadian Prairies and it was used to assess the impact of canola on the community of AMF naturally occurring in three cropping systems, canola monoculture, or canola in two different rotation systems (2-years, canola-wheat and 3-years, barley-pea-canola). We sampled canola rhizosphere and bulk soils to: (i) determine diversity and community structure of AMF, we expected that canola will negatively impact AMF communities in function of its frequency in crop rotations and (ii) wanted to assess how these AMF communities interact with other fungi and bacteria. We detected 49 AMF amplicon sequence variants (ASVs) in canola rhizosphere and bulk soils, confirming the persistence of a diversified AMF community in canola-planted soil, even after 10 years of canola monoculture, which was unexpected considering that canola is among non-mycorrhizal plants. Network analysis revealed a broad range of potential interactions between canola-associated AMF and some fungal and bacterial taxa. We report for the first time that two AMF, Funneliformis mosseae and Rhizophagus iranicus, shared their bacterial cohort almost entirely in bulk soil. Our results suggest the existence of non-species-specific AMF-bacteria or AMF-fungi relationships that could benefit AMF in absence of host plants. The persistence of an AMF community in canola rhizosphere and bulk soils brings a new light on AMF ecology and leads to new perspectives for further studies about AMF and soil microbes interactions and AMF subsistence without mycotrophic host plants.

Ectomycorrhizal Fungi Dominated the Root and Rhizosphere Microbial Communities of Two Willow Cultivars Grown for Six-Years in a Mixed-Contaminated Environment

There is a growing interest in plant microbiome’s engineering to optimize desired functions such as improved phytoremediation. This study is aimed at examining the microbial communities inhabiting the roots and rhizospheres of two Salix miyabeana cultivars that had been grown in a short-rotation intensive culture (SRIC) system for six years in a soil contaminated with the discharge from a petrochemical factory. DNA was extracted from roots and rhizospheric soils, and fungal ITS and bacterial and archaeal 16S rDNA regions were amplified and sequenced using Illumina MiSeq technology. Cultivars ‘SX61’ and ‘SX64’ were found to harbor a similar diversity of fungal, bacterial, and archaeal amplicon sequence variants (ASVs). As expected, a greater microbial diversity was found in the rhizosphere biotope than in the roots of both cultivars, except for cultivar ‘SX64’, where a similar fungal diversity was observed in both biotopes. However, we found that microbial community structures were cultivar- and biotope-specific. Although the implication of some identified taxa for plant adaptability and biomass production capacity remains to be explored, this study provides valuable and useful information regarding microbes that could potentially favor the implantation and phytoremediation efficiency of Salix miyabeana in mixed contamination sites in similar climatic environments.

Biodiversity of arbuscular mycorrhizal fungi in plant roots and rhizosphere soil from different arid land environment of Qatar

Recently more attention has been observed toward the role of arbuscular mycorrhizal fungi (AMF) in plant growth. Qatar belongs to the Arabian Gulf region with hot and dry climatic conditions. The study aims to investigate the species composition and abundance of AMF in Qatar, rhizosphere soil samples, and roots of plants from 12 families and 8 different locations. The AMF were identified based on the sequencing of the polymerase chain reaction (PCR) product of the amplified conserved ITS region. The reported AMF infection rate was found to vary with location and plant species. Tamarix aphylla recorded the highest AMF infection rate (100%), followed by Blepharis ciliaris (98%) and Sporobolus ioclados (92%). AMF spore counts ranged from 29.3 spores in Blepharis ciliaris to 643 spores/100 g soil in Fagonia indica. No correlation was detected between colonization rate and spore counts. While all AMF identified at species levels were reported in other regions, new species are still expected since some were identified only at higher taxonomic levels. Claroideoglomus drummondii and Rhizophagus irregularis were the most widespread while Claroideoglomus claroideum and Diversispora aurantia were the least present. Our results fill the gap of knowledge of AMF in the region and opens new research toward its future applications for sustainable agriculture.

A historical perspective on mycorrhizal mutualism emphasizing arbuscular mycorrhizas and their emerging challenges

Arbuscular mycorrhiza, one of the oldest interactions on earth (~ 450 million years old) and a first-class partner for plants to colonize emerged land, is considered one of the most pervasive ecological relationships on the globe. Despite how important and old this interaction is, its discovery was very recent compared to the long story of land plant evolution. The story of the arbuscular mycorrhiza cannot be addressed apart from the history, controversies, and speculations about mycorrhiza in its broad sense. The chronicle of mycorrhizal research is marked by multiple key milestones such as the initial description of a "persistent epiderm and pellicular wall structure" by Hartig; the introduction of the "Symbiotismus" and "Mycorrhiza" concepts by Frank; the description of diverse root-fungal morphologies; the first description of arbuscules by Gallaud; Mosse's pivotal statement of the beneficial nature of the arbuscular mycorrhizal symbiosis; the impact of molecular tools on the taxonomy of mycorrhizal fungi as well as the development of in vitro root organ cultures for producing axenic arbuscular mycorrhizal fungi (AMF). An appreciation of the story - full of twists and turns - of the arbuscular mycorrhiza, going from the roots of mycorrhiza history, along with the discovery of different mycorrhiza types such as ectomycorrhiza, can improve research to help face our days' challenge of developing sustainable agriculture that integrates the arbuscular mycorrhiza and its ecosystem services.