Arbuscular Mycorrhizal Fungi Strains Research Articles

Arbuscular mycorrhizal fungi improves yield and quality attributes of melon fruit grown under greenhouse

ABSTRACT Melon (Cucumis melo) is the most popular fruit with indisputable socio-economic and nutritional value, as evidenced by its significant acreage (1 Mha) and production (28 Mt) worldwide. However, melon farming is facing the triple challenge of producing enough to meet growing consumer demand, improving the concentration of human wellness compounds, while minimising chemical inputs. This scientific research was carried out to assess the effectiveness of two arbuscular mycorrhizal fungi (AMF), Rhizophagus irregularis (Ri), R. fasciculatus (Rf), and their complex, in improving yield and quality attributes in melon variety ‘Ananas’ grown in greenhouse. Results showed that production and fruit quality were significantly improved in mycorrhizal plants (M-plants) compared to non-mycorrhizal (NM-plants) ones, regardless of AMF treatments. M-plants performance varied according to AMF strains. Indeed, Ri-plant exhibited the highest increases in yield (54%), fresh weight (65%), longitudinal (20%) and equatorial (33%) perimeters, Brix degree (20.6%), polyphenols (315.4%), carotenoids (353%), proteins (209.1%), flavonoids (114.38%), ascorbic acid (31.3%), reducing power (77.04%), DPPH radical inhibition (16.43%), and the highest decrease in titrable acidity (62.5%). In addition, Ri-plant fruits were highly rated by participants in the sensory evaluation test. Therefore, R. irregularis application could be recommended for the sustainable production of high-quality fruits of melon.

Groundnut (Arachis hypogeae L.) production, soil biological characteristics, micronutrient content in soil and plant parts, and their uptake are all influenced by phosphorus, AMF and PSB application

Field experiments during rabi seasons of 2017-18 and 2018-19 were conducted to asses the groundnut production, soil biological characteristics, micronutrient content in soil and plant parts, and their uptake influenced by graded levels of phosphorus (15, 30, 45 and 60 kg ha−1), Arbuscular Mycorrhizal Fungi (AMF) and Phosphorus Solubilizing Bacteria (PSB) application in Alfisols at Botany farm, Dr. BSKKV, Dapoli in a factorial randomized block design with twenty treatment combinations which were replicated thrice. Results indicated that higher dose of phosphours (60 kg ha−1), biofertilizers (AMF + PSB @ 10 kg ha−1 each) and their interaction was found prominent in augmenting the highest bacterial, actinomycetes, fungal populations. Further, the combined application of phosphate and the AMF and PSB strain at higher level significantly improved the enzyme activities viz., dehydrogenase, urease, alkaline and acid phosphatase, CO2 evolution and SMBC compared to lower dose of phosphorus and non-inoculated treatment was on par with application of phosphorus @ 45 kg ha−1 with dual inoculation of AMF + PSB @ 10 kg ha−1 each. However, DTPA-extractable micronutrients (Fe, Mn, Zn and Cu) status showed significant improvement because of various treatment combinations. Similarly, the application of phosphorus @ 60 kg ha−1 exhibited the highest uptake in edible portion of crops which was resulted in significantly highest pod yield (35.86 q ha−1) of groundnut which was at par with application of phosphorus @ 45 kg ha−1 (31.96 q ha−1) indicating beneficial effect for improving as well sustaining soil health in long term aspects.

Building blocks toward sustainable biofertilizers: variation in arbuscular mycorrhizal spore germination when immobilized with diazotrophic bacteria in biodegradable hydrogel beads.

We investigated whether there was interspecies and intraspecies variation in spore germination of 12 strains of arbuscular mycorrhizal fungi when co-entrapped with the diazotrophic plant growth-promoting bacteria, Azospirillum brasilense Sp7 in alginate hydrogel beads. Twelve Rhizophagus irregularis, Rhizophagus intraradices, and Funneliformis mosseae strains were separately combined with a live culture of Azospirillum brasilense Sp7. Each fungal-bacterial consortia was supplemented with sodium alginate to a 2% concentration (v/v) and cross-linked in calcium chloride (2%w/v) to form biodegradable hydrogel beads. One hundred beads from each combination (total of 1200) were fixed in solidified modified Strullu and Romand media. Beads were observed for successful spore germination and bacterial growth over 14 days. In all cases, successful growth of A. brasilense was observed. For arbuscular mycorrhizal fungi, interspecies variation in spore germination was observed, with R. intraradices having the highest germination rate (64.3%), followed by R. irregularis (45.5%) and F. mosseae (40.3%). However, a difference in intraspecies germination was only observed among strains of R. irregularis and F. mosseae. Despite having varying levels of germination, even the strains with the lowest potential were still able to establish with the plant host Brachypodium distachyon in a model system. Arbuscular mycorrhizal spore germination varied across strains when co-entrapped with a diazotrophic plant growth-promoting bacteria. This demonstrates that hydrogel beads containing a mixed consortium hold potential as a sustainable biofertilizer and that compatibility tests remain an important building block when aiming to create a hydrogel biofertilizer that encases a diversity of bacteria and fungi. Moving forward, further studies should be conducted to test the efficacy of these hydrogel biofertilizers on different crops across varying climatic conditions in order to optimize their potential.

Sustainable Remediation of Soil and Water Utilizing Arbuscular Mycorrhizal Fungi: A Review.

Phytoremediation is recognized as an environmentally friendly technique. However, the low biomass production, high time consumption, and exposure to combined toxic stress from contaminated media weaken the potential of phytoremediation. As a class of plant-beneficial microorganisms, arbuscular mycorrhizal fungi (AMF) can promote plant nutrient uptake, improve plant habitats, and regulate abiotic stresses, and the utilization of AMF to enhance phytoremediation is considered to be an effective way to enhance the remediation efficiency. In this paper, we searched 520 papers published during the period 2000-2023 on the topic of AMF-assisted phytoremediation from the Web of Science core collection database. We analyzed the author co-authorship, country, and keyword co-occurrence clustering by VOSviewer. We summarized the advances in research and proposed prospective studies on AMF-assisted phytoremediation. The bibliometric analyses showed that heavy metal, soil, stress tolerance, and growth promotion were the research hotspots. AMF-plant symbiosis has been used in water and soil in different scenarios for the remediation of heavy metal pollution and organic pollution, among others. The potential mechanisms of pollutant removal in which AMF are directly involved through hyphal exudate binding and stabilization, accumulation in their structures, and nutrient exchange with the host plant are highlighted. In addition, the tolerance strategies of AMF through influencing the subcellular distribution of contaminants as well as chemical form shifts, activation of plant defenses, and induction of differential gene expression in plants are presented. We proposed that future research should screen anaerobic-tolerant AMF strains, examine bacterial interactions with AMF, and utilize AMF for combined pollutant removal to accelerate practical applications.

Bioinoculation Effect of Frankia sp. and Microbial Bioagents on Growth and Development of Elaeagnus latifolia L. seedlings: An Endangered Plant Species of North East India

Aims: Analyses were done on the role of rhizospheric symbiotic Arbuscular Mycorrhizal (AM) fungus, Non-AM fungus and a bacterium in growth and development of E. latifolia L. seedlings. Study Design and Methodology: The seedlings were inoculated with recognized AM fungal strain (Glomus mosseae, Gm 1), non-AM fungus (Trichoderma harzianum, Th-13) alone and nitrogen fixing bacteria Frankia sp. in combined form (both, dual and triple/ tripartite consortium) and analysed for their effect on growth parameters i.e. increase in length, diameter, circumference, Sturdiness quotient (Sq), Biovolume index (Bi) and Plastochron interval index (Pi) of the target plant species. Results: Qualitative analysis have revealed that the consortium treatment containing Glomus mosseae and Frankia sp. (FS-03) resulted in more increase in the length (7.0 ±0.25 cm), diameter (1.3 ±0.25 cm), circumference while the highest biovolume index was observed in the consortium treatment of Frankia sp. along with Glomus mosseae, Trichoderma harzianum viz. Fs-04 (280.96 ± 20.0) and sturdiness quotient of 0.25 including reduced phyto-mortality and initiating rapid phyllogenesis in inoculated seedlings as compared to control seedlings. In contrast to control seedlings, which are covered in depth in this work, a similar pattern with negligible variance in all analyzed parameters as indicated above were also seen in other alone and combined treatments. Conclusion: As a result, it was shown that both AM alone and consortium inoculations with Frankia sp. increased this plant species' adaptation and resilience.

Physiological and Enzymatic Antioxidant Responses of Solanum tuberosum Leaves to Arbuscular Mycorrhizal Fungal Inoculation under Water Stress.

Solanum tuberosum is one of the most widely cropped plant species worldwide; unfortunately, drought is one of the major constraints on potato productivity because it affects the physiology, biochemical processes, and yield. The use of arbuscular mycorrhizal fungi (AMF) has exhibited beneficial effects on plants during drought. The objective of this study was to analyse the effect of AMF inoculation on two genotypes of potato plants exposed to water stress, and the photosynthetic traits, enzymatic antioxidant activity, and exudation of low-molecular-weight organic acids (LMWOAs) of potato plants inoculated with two strains of AMF, Claroideoglomus claroideum (CC) and Claroideoglomus lamellosum (HMC26), were evaluated. Stomatal conductance exhibited a similar trend in the CC and HMC26 treatments for both potato genotypes; moreover, the photosynthetic rate significantly increased by 577.9% between the 100% soil humidity (S0) and 40% soil humidity (S2) stress levels for the VR808 genotype under the CC treatment. The activities of the enzymes catalase (CAT) and ascorbate peroxidase (APX) showed similar trends. In this study, there were different responses among genotypes and treatments. Inoculation with CC under S2 stress levels is a promising potential approach for improving potato growth under drought conditions.

Improving vanadium removal from contaminated river water in constructed wetlands: The role of arbuscular mycorrhizal fungi

Industrial activities pose a significant ecological risk to water resources as they pollute surrounding waters with vanadium (V). Although the contribution of plants and substrates to V removal in constructed wetlands (CWs) has been reported, the role of arbuscular mycorrhizal fungi (AMF) is unclear. The aim of the present study was to investigate the role of AMF in V removal in CWs and to elucidate the underlying mechanisms. Reed plants (Phragmites australis) were inoculated with an AMF strain (Rhizophagus irregularis) in CW columns, creating AMF-inoculated (+AMF) and non-inoculated (-AMF) treatments. Three levels of influent V concentrations (low: 0.50 mg L−1, medium: 1.14 mg L−1 and high: 1.52 mg L−1) were examined. The + AMF treatment showed higher V removal (60%–98%) than the control (40%–82%) in all three conditions, although the difference was not significant in some cases. The mean mycorrhizal effects were 75%, 19%, and 28% for low, moderate, and high influent V concentrations, respectively. The +AMF treatment showed a higher GRSP-bonded V concentration (5.5 mg g−1) than the -AMF treatment (4.0 mg g−1). Furthermore, +AMF treatment showed larger plants with higher V concentrations in their tissues, accompanied by increased biological concentration factors and biological accumulation factors. Given the remarkable positive effect of AMF on V removal, our study suggests that treating AMF in CWs is a worthwhile approach.

Elevating Sorghum Prosperity: Unveiling Growth Trends through Phosphate-Solubilizing Bacteria and Arbuscular Mycorrhizal Fungi Inoculation in Phosphate-Enriched Substrates

This study aimed to elucidate the impact of phosphate-solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) inoculation on sorghum growth within substrates derived from phosphate solid sludge, with the overarching objective of repurposing phosphate sludge to be a viable agricultural substrate. Four PSB strains (Serratia rubidaea, Enterobacter bugandensis, Pantoea agglomerans, Pseudomonas sp.) were meticulously selected from phosphate solid sludge, along with two AMF strains (Rhizophagus intraradices and Funneliformis mosseae), constituting the experimental inocula. Phosphate solid sludge was judiciously blended with peat at varying volumetric proportions (0%, 10%, 20%, 40%, and 60%), providing the matrix for sorghum cultivation, and concomitantly subjected to inoculation with PSB and AMF. Following a meticulously monitored two-month duration, a comprehensive evaluation of diverse morphological parameters, biomass accrual, nitrogen content, total phosphorus concentration, potassium levels, calcium content, and root colonization in sorghum plants was conducted. The empirical findings underscored a discernible decline in the assessed parameters with escalating concentrations of phosphate solid sludge. Particularly noteworthy was the pronounced amelioration observed in plants inoculated with AMF in comparison to both the control and PSB-inoculated counterparts. In conclusion, the application of raw phosphate solid sludge as an agricultural substrate is deemed unsuitable, prompting the imperative need for further in-depth investigations to ascertain the nuanced intricacies underlying these outcomes.

Use of arbuscular mycorrhizal fungi (AMF) in the nutrition of <i>Leucacephala leucocephala </i>(Lam.) De wit for forage production

At present, the use of biofertilizers and protein plants in the nutrition of pastures and forage has increased. The investigation was carried out in the University Center of the municipality of Cumanayagua, county of Cienfuegos, Cuba with the objective of evaluating the response of Leucaena leucocephala (Lam.) De Wit to the inoculation of different arbuscular mycorrhizal fungi (AMF) strains. The experiment was carried out in polyethylene bags. The experiment used a random blocks design with three replicates and the following treatments: #1. Soil (Control treatment, without inoculation and NPK application), #2. Soil + inoculation with the AMF strain F. mosseae/INCAM-2, #3. Soil + inoculation with the AMF strain G. cubense/INCAM-4) and #4. Soil + NPK fertilization at plant establishment application of NPK (25, 40 y 120 kg ha-1 de N, P2O5 y K20) + N at each cut at 70% of the initial dose. The inoculation with AMF was simultaneous for all treatments. A establishment cut and five successive cuts were performed, with 51.33 average days between them. The biomass production, the content of gross protein of L. leucocephala in each harvest and the cumulative total, as well as mycorrhizal effectiveness, were quantified. L. leucocephala positively responded to F. mosseae/INCAM-2 inoculation. Biomass production for cut increased between 31,50 % (Treatment #2) y 19,40 % (Treatment #3) with respect to control treatment. Inoculation with F. mosseae/INCAM-2 showed higher mycorrhizal effectiveness. The highest value in gross protein was obtained in the variant with mineral fertilization and the inoculated variants overcame the control treatment, with better performance than treatment # 2 ( Soil+ Funneliformis mosseae/INCAM-2).

Effects of fungal endophytes and arbuscular mycorrhizal fungi on growth of Echium vulgare and alkannin/shikonin and their derivatives production in roots

Endophytic fungi as well as arbuscular mycorrhizal fungi (AMF) are known to stimulate plant growth and production of secondary metabolites in medicinal plants. Here, 10 endophytic fungi isolated from roots of wild Alkanna tinctoria plants and 5 AMF purchased from the Glomeromycota in vitro collection were evaluated, during two successive three-month greenhouse experiments, on the growth of Echium vulgare and alkannin/shikonin and their derivatives (A/Sd) production in the roots. Some of the endophytic fungi tested significantly increased plant growth parameters as compared to the control: Cladosporium allicinum, Cadophora sp., Clonostachys sp., Trichoderma hispanicum and Leptosphaeria ladina increased root volume, Plectosphaerella sp. And T. hispanicum root fresh weight and root water retention and T. hispanicum plant water retention. However, none of these fungi impacted A/Sd production. Conversely, none of the AMF strains tested impacted plant growth parameters, but those inoculated with Rhizophagus intraradices MUCL 49410 had a significantly higher concentration of alkannin/shikonin (A/S), acetyl-A/S, β,β– dimethylacryl-A/S, isovaleryl-A/S and total A/Sd, compared to the control plants. Further studies are needed to investigate the mechanisms involved in the production of A/Sd in plants associated to specific endophytic fungi/AMF and on the cultivation conditions required for optimal production of these compounds.

Antioxidant Response, Phenolic Compounds and Yield of Solanum tuberosum Tubers Inoculated with Arbuscular Mycorrhizal Fungi and Growing under Water Stress.

Solanum tuberosum (potato) is one of the most common crops worldwide; however, it is sensitive to water stress, which necessitates the identification of alternative tools to improve their production. Here, we evaluated the inoculation of two arbuscular mycorrhizal fungi (AMF) strains, Claroideoglomus claroideum (CC), Claroideoglomus lamellosum (HMC26), and the MIX (CC + HMC26) in yield and phenolic and antioxidant response using chromatographic and spectroscopic methods in potato crops, at increasing levels of water stress, namely, with 100% (0), 70% (S1), and 40% (S2) soil humidity. Two caffeoylquinic acid isomers were detected and their levels showed a tendency to increase under stress together with the AMF inoculation, reaching up to 19.2 mg kg-1 of 5-caffeoylquinic acid and 7.4 mg kg-1 of caffeoylquinic acid isomer when CC was inoculated, and potato plants grew at the highest water starvation condition (S2). Regarding antioxidant activities, a differentiated response was detected depending on the AMF strain, highlighting the effect of HMC26 on Trolox equivalent antioxidant capacity (TEAC) method and CC in cupric reducing antioxidant capacity (CUPRAC) method, reaching up to 1.5 μmol g-1 of TEAC in plants inoculated with HMC26 and 0.9 μmol g-1 of CUPRAC in plants inoculated with CC, both in potato tubers of plants growing under the S2 stress condition. Meanwhile, the use of AMF did not influence the number and biomass of the tubers, but significant changes in the biochemical properties of tubers were observed. The results suggest that specific AMF adaptations to water stress must be considered when inoculation procedures are planned to improve the yield and quality of tubers in potato crops.

Genotypic variation of tomato to AMF inoculation in improving growth, nutrient uptake, yield, and photosynthetic activity

Arbuscular mycorrhizal fungi (AMF) promote water and mineral nutrients uptake by plant roots, which can reduce the chemical fertilizer inputs in crop production. To gain better insight into the comparative effect of different strains of AMF in improving tomato performance at morphological and physiological levels, seedlings of two tomato cultivars (i.e., Better Boy and Roma) were inoculated with four strains of Glomus mosseae (i.e., HS 1–2, BEG 12, BEG 55, and BEG 54) under greenhouse conditions. Results showed that tomato growth and yield varied largely depending on the mycorrhizal strain and tomato cultivar, with wide variations in root colonization ranging from 5.30 to 78.63%. Overall, mycorrhization with BEG 54 showed significantly better tomato performance when compared to the BEG 55, HS 1–2 and BEG 12 strains. In the case of cultivars, Better Boy performed better than Roma cultivar in terms of growth, physiological traits, yield, and fruit quality. The highest plant height, dry matter, nitrogen, phosphorus, potassium, chlorophyll a, chlorophyll b, AMF colonization, yield, fruit juice, ascorbic acid, and titratable acidity contents were recorded in Better Boy cultivar while the highest stem diameter was found in Roma cultivar. Taken together, AMF colonization suggested a promising approach for large-scale tomato production by efficient absorption and utilization of nutrients, and encouraging plants’ symbiotic relationships with soil microorganisms.

Allelopathy and arbuscular mycorrhizal fungi interactions shape plant invasion outcomes

The novel weapon hypothesis suggests that allelopathy is an important mechanism for exotic plants to successfully invade native plant communities. Allelochemicals from exotic plants affect both native plants and arbuscular mycorrhizal fungi (AMF) in soil. To explore these effects, we conducted pot experiments using a native plant community comprising of Chenopodium album L., Vitex negundo L., Rhus chinensis Mill., and Acer truncatum Bunge. We incorporated AMF strains (Funneliformis mosseae, Glomus versiforme, and Rhizophagus intraradices in a 1:1:1 volume ratio) into a soil mixture comprising equal volumes of autoclaved field soil and grass ash at five concentrations (0 g L–1, CK; 10 g L–1, LRE; 20 g L–1, NRE; 30 g L–1, MRE; and 40 g L–1, HRE) to investigate the allelopathy of Rhus typhina L. root and its interactions with AMF on the native plant community. Our results indicated that low concentrations of allelochemicals promoted the relative growth rate and leaf nitrogen content in the native plant community, which was attributed to the increased environmental stress that improved the degree of leaf photosynthetic capacity and organic synthesis rate in the native communities. Moreover, allelochemicals with toxicity decreased the colonization rates of AMF. Meanwhile, the presence of allelopathic effects induced a decrease in leaf nitrogen, and allelopathy altered the effects of AMF on the native community. Specifically, the high concentration of allelochemicals altered the positive effect of AMF on the total aboveground biomass of the native plant community to a negative effect, likely by decreasing colonization rates or affecting soil physicochemical properties and the composition of the mycorrhizal communities. Consequently, it is necessary to consider the effects of AMF when testing the roles of allelopathy or the novel weapons hypothesis in biological invasions. Graphical abstract

Rhizoglomus variabile and Nanoglomus plukenetiae, Native to Peru, Promote Coffee Growth in Western Amazonia.

Coffee (Coffea arabica) is among the world's most economically important crops. Coffee was shown to be highly dependent on arbuscular mycorrhizal fungi (AMF) in traditionally managed coffee plantations in the tropics. The objective of this study was to assess AMF species richness in coffee plantations of four provinces in Perú, to isolate AMF isolates native to these provinces, and to test the effects of selected indigenous AMF strains on coffee growth. AMF species were identified by morphological tools on the genus level, and if possible further to the species level. Two native species, Rhizoglomus variabile and Nanoglomus plukenetiae, recently described from the Peruvian mountain ranges, were successfully cultured in the greenhouse on host plants. In two independent experiments, both species were assessed for their ability to colonize coffee seedlings and improve coffee growth over 135 days. A total of 35 AMF morphospecies were identified from 12 plantations. The two inoculated species effectively colonized coffee roots, which resulted in 3.0-8.6 times higher shoot, root and total biomass, when compared to the non-mycorrhizal controls. R. variabile was superior to N. plukenetiae in all measured parameters, increasing shoot, root, and total biomass dry weight by 4.7, 8.6 and 5.5 times, respectively. The dual inoculation of both species, however, did not further improve plant growth, when compared to single-species inoculations. The colonization of coffee by either R. variabile or N. plukenetiae strongly enhances coffee plant growth. R. variabile, in particular, offers enormous potential for improving coffee establishment and productivity. Assessment of further AMF species, including species from other AMF families should be considered for optimization of coffee growth promotion, both alone and in combination with R. variabile.

Impact of Arbuscular mycorrhizal Fungal Strains Isolated from Soil on the Growth, Yield, and Fruit Quality of Tomato Plants under Different Fertilization Regimens

Arbuscular mycorrhizal fungi (AMF) have emerged as a promising and environmentally friendly solution for sustainable agriculture, offering a reduction in dependence on chemical inputs. The objective of this greenhouse experiment was to assess the efficacy of a natural endomycorrhizal inoculum obtained from leek root fragments, which acted as a trap plant to capture indigenous fungal spores present in the soil of the Guercif region in Morocco. The investigation aimed to comprehensively evaluate the influence of this inoculum on various parameters related to tomato plant growth, yield, and sensory quality. Additionally, different levels of chemical fertilizers, equivalent to 50%, 75%, and 100% of the recommended dosage, were administered in combination with or without the inoculum. The findings elucidated significant advantages associated with mycorrhizal inoculation. The plants subjected to inoculation exhibited increased plant height, augmented leaf and root dry weights, and improved nutrient uptake compared to the control group. Notably, tomato plants treated with 75% of the recommended chemical fertilizer dosage yielded the highest crop production, with no statistically significant difference observed when compared to those receiving the full dosage (100%). Intriguingly, tomato plants grown in substrates receiving 50% chemical fertilizers demonstrated the highest levels of mycorrhization, exhibiting a frequency (F) of 100% and an intensity (M) of 63%. Importantly, the combination of inoculation with a reduced dose of NPK fertilizer (50% of the recommended amount) resulted in significantly elevated concentrations of calcium (Ca), potassium (K), iron (Fe), zinc (Zn), and phosphorus (P) in the plants, attributable to the heightened mycorrhizal colonization of the roots. In terms of fruit characteristics, no significant variations were detected in pH and electrical conductivity (EC) among the treatment groups. However, the inoculated plants exhibited a notable increase in the Brix index, an indicator of sweetness, compared to the control group across all fertilizer doses. Furthermore, inoculation positively influenced the levels of total carotenoids in the fruits. Remarkably, the values of these compounds in the inoculated plants subjected to 50% of the recommended fertilizer dosage surpassed those recorded in the non-inoculated plants receiving the full dosage.

Arbuscular mycorrhizal fungi impact the production of alkannin/shikonin and their derivatives in Alkanna tinctoria Tausch. grown in semi-hydroponic and pot cultivation systems.

Alkanna tinctoria Tausch. is a medicinal plant well-known to produce important therapeutic compounds, such as alkannin/shikonin and their derivatives (A/Sd). It associates with arbuscular mycorrhizal fungi (AMF), which are known, amongst others beneficial effects, to modulate the plant secondary metabolites (SMs) biosynthesis. However, to the best of our knowledge, no study on the effects of AMF strains on the growth and production of A/Sd in A. tinctoria has been reported in the literature. Here, three experiments were conducted. In Experiment 1, plants were associated with the GINCO strain Rhizophagus irregularis MUCL 41833 and, in Experiment 2, with two strains of GINCO (R. irregularis MUCL 41833 and Rhizophagus aggregatus MUCL 49408) and two native strains isolated from wild growing A. tinctoria (R. irregularis and Septoglomus viscosum) and were grown in a semi-hydroponic (S-H) cultivation system. Plants were harvested after 9 and 37 days in Experiment 1 and 9 days in Experiment 2. In Experiment 3, plants were associated with the two native AMF strains and with R. irregularis MUCL 41833 and were grown for 85 days in pots under greenhouse conditions. Quantification and identification of A/Sd were performed by HPLC-PDA and by HPLC-HRMS/MS, respectively. LePGT1, LePGT2, and GHQH genes involved in the A/Sd biosynthesis were analyzed through RT-qPCR. In Experiment 1, no significant differences were noticed in the production of A/Sd. Conversely, in Experiments 2 and 3, plants associated with the native AMF R. irregularis had the highest content of total A/Sd expressed as shikonin equivalent. In Experiment 1, a significantly higher relative expression of both LePGT1 and LePGT2 was observed in plants inoculated with R. irregularis MUCL 41833 compared with control plants after 37 days in the S-H cultivation system. Similarly, a significantly higher relative expression of LePGT2 in plants inoculated with R. irregularis MUCL 41833 was noticed after 9 versus 37 days in the S-H cultivation system. In Experiment 2, a significant lower relative expression of LePGT2 was observed in native AMF R. irregularis inoculated plants compared to the control. Overall, our study showed that the native R. irregularis strain increased A/Sd production in A. tinctoria regardless of the growing system used, further suggesting that the inoculation of native/best performing AMF is a promising method to improve the production of important SMs.

Contribution of Arbuscular Mycorrhizal and Endophytic Fungi to Drought Tolerance in Araucaria araucana Seedlings.

In its natural distribution, Araucaria araucana is a plant species usually exposed to extreme environmental constraints such as wind, volcanism, fires, and low rainfall. This plant is subjected to long periods of drought, accentuated by the current climate emergency, causing plant death, especially in its early growth stages. Understanding the benefits that both arbuscular mycorrhizal fungi (AMF) and endophytic fungi (EF) could provide plants under different water regimes would generate inputs to address the above-mentioned issues. Here, the effect of AMF and EF inoculation (individually and combined) on the morphophysiological variables of A. araucana seedlings subjected to different water regimes was evaluated. Both the AMF and EF inocula were obtained from A. araucana roots growing in natural conditions. The inoculated seedlings were kept for 5 months under standard greenhouse conditions and subsequently subjected to three different irrigation levels for 2 months: 100, 75, and 25% of field capacity (FC). Morphophysiological variables were evaluated over time. Applying AMF and EF + AMF yielded a noticeable survival rate in the most extreme drought conditions (25% FC). Moreover, both the AMF and the EF + AMF treatments promoted an increase in height growth between 6.1 and 16.1%, in the production of aerial biomass between 54.3 and 62.6%, and in root biomass between 42.5 and 65.4%. These treatments also kept the maximum quantum efficiency of PSII (Fv/Fm 0.71 for AMF and 0.64 for EF + AMF) stable, as well as high foliar water content (>60%) and stable CO2 assimilation under drought stress. In addition, the EF + AMF treatment at 25% FC increased the total chlorophyll content. In conclusion, using indigenous strains of AMF, alone or in combination with EF, is a beneficial strategy to produce A. araucana seedlings with an enhanced ability to tolerate prolonged drought periods, which could be of great relevance for the survival of these native species under the current climate change.

Impacts of Tillage Practices on Growth, Phosphorus Uptake, and Yield of Maize in Controlled and Field-Based Studies in Relation to Arbuscular Mycorrhizal Fungi

This study investigated the effects of arbuscular mycorrhizal fungi (AMF) on the growth, phosphorus (P) uptake, and yield of maize in the presence or absence of tillage. The two-year field experiment was conducted in Kanagawa, Japan. Firstly, we investigated whether the presence of indigenous AMF communities in the roots, as determined by amplicon sequencing analysis, contributed to maize growth in Experiment 1, a 2-year field-based study. The findings revealed that the maize (Zea mays L.) in rotary tillage had higher P uptake, growth at the six-leaves collar stage, and yield, compared to no tillage. The AMF communities colonizing maize roots were altered by the presence or absence of tillage; specifically, tillage increased the dominance of the Gigasporaceae, whereas no tillage increased the dominance of the Acaulosporaceae. Based on these findings, we confirmed whether the inoculation of similar AMF strains, as analyzed in the field study of tillage practices on maize roots, produces growth-promoting effects for maize growth in a controlled pot experiment consistent with the results of the field experiment. For experiment 2, Dentiscutata cerradensis TK-1, Cetraspora pellucida SZ-3 (Gigasporaceae), Acaulospora morrowiae AP-5, and A. longula F-1 (Acaulosporaceae) were inoculated as AMF inocula for a pot experiment. The results showed that aboveground biomass did not change with any inoculum compared to the control. The P concentration in maize was higher for D. cerradensis TK-1 and C. pellucida SZ-3 inoculation than for the control. However, inoculation with A. morrowiae AP-5 and A. longula F-1 did not change P concentrations from the control. This indicates that D. cerradensis TK-1 and C. pellucida SZ-3 are more effective in promoting P uptake in maize than in A morrowiae AP-5 and A. longula F-1. Based on field and pot experiments, our findings suggest that tillage practices lead to alterations in the AMF communities that colonize the roots, and this shift may also contribute to changes in P uptake and crop growth.

Engineering Approach for Production of Arbuscular Mycorrhizal Inoculum Adapted to Saline Soil Management

(1) Background: Soil salinity impacts plant growth and productivity in steppic regions. Thus, the current study aims at producing, at low cost, an inoculum composed of native arbuscular mycorrhizal fungi (AMF) strains adapted to saline soil management. (2) Methods: The propagation of the native AMF strains was carried out in three natural saline soils presenting increasing salinity levels (4.5, 8.5 and 9.3 dS·m−1 in Boughzoul (BG), Salt Rocket (SR) and Zaafrane (ZA) sites, respectively). Three host plant species (alfalfa, clover and leek) were tested as trap cultures. AMF spore richness and diversity, the quantification of soil microbial biomass and the determination of the most probable number (MPN) were carried out before and after 24 months culture. Moreover, the mycorrhizal rates of the host plant species were assessed. (3) Results: The moderate saline soil (SR) planted with alfalfa was found to be the most suitable for AMF inoculum production with a maximum of 650 spores, 10 g−1 of soil, a mycorrhizal rate of 86%, 70 propagules·g−1 of soil and the highest microbial biomass content. (4) Conclusion: This study points out the best combination for the production of a more adapted AMF biofertilizer for saline soil management and proposes several indicators for biofertilizer quality evaluation.

The function and community structure of arbuscular mycorrhizal fungi in ecological floating beds used for remediation of Pb contaminated wastewater

Arbuscular mycorrhizal fungi (AMF) have been demonstrated to be ubiquitous in aquatic ecosystems. However, their distributions and ecological functions are rarely studied. To date, a few studies have combined sewage treatment facilities with AMF to improve removal efficiency, but appropriate and highly tolerant AMF strains have not been explored, and the purification mechanisms remain unclear. In this study, three ecological floating-bed (EFB) installations inoculated with different AMF inocula (mine AMF inoculum, commercial AMF inoculum and non-AMF inoculated) were constructed to investigate their removal efficiency for Pb-contaminated wastewater. The AMF community structure shifts in the roots of Canna indica inhabiting EFBs during the three phases (pot culture phase, hydroponic phase and hydroponic phase with Pb stress) were tracked utilizing quantitative real-time polymerase chain reaction and Illumina sequencing techniques. Furthermore, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to detect the Pb location in mycorrhizal structures. The results showed that AMF could promote host plant growth and enhance the Pb removal efficiency of the EFBs. The higher the AMF abundance, the better the effect of the AMF on Pb purification by EFBs. Both flooding and Pb stress decreased the AMF diversity but did not significantly inhibit the abundance. The three inoculation treatments showed different community compositions with different dominant AMF taxa in different phases, and an uncultured Paraglomus species (Paraglomus sp. LC516188.1) was found to be the most dominant (99.65 %) AMF in the hydroponic phase with Pb stress. The TEM and EDS analysis results showed that the Paraglomus sp. could accumulate Pb in plant roots through their fungal structures (intercellular mycelium, intracellular mycelium, etc.), which alleviated the toxic effect of Pb on plant cells and limited Pb translocation. The new findings provide a theoretical basis for the application of AMF in plant-based bioremediation of wastewater and polluted waterbodies.