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In forests, mycorrhizal fungi regulate carbon (C) and nitrogen (N) dynamics. We evaluated the interplay among ectomycorrhizas (ECM), ecosystem C fluxes, tree productivity, C and N exchange and isotopic fractionation along the soil‐ECM‐plant continuum in a Mediterranean beech forest. From bud break to leaf shedding, we monitored: net ecosystem exchange (NEE, a measure of the net exchange of C between an ecosystem and the atmosphere), leaf area index, stem growth, N concentration, δ13C and δ15N in rhizosphere soil, ectomycorrhizal fine root tips (ERT), ECM‐free fine root portions (NCR) and leaves. Seasonal changes in ERT relative biomass were strictly related to NEE and mimicked those detected in the radial growth. The analysis of δ13C in ERT, leaves and NCR highlighted the impact of canopy photosynthesis on ERT development and an asynchronous seasonal C allocation strategy between ERT and NCR at the root tips level. Concerning N, δ15N of leaves was negatively related to that of ERT and dependent on seasonal 15N differences between ERT and NCR. Our results unravel a synchronous C allocation towards ERT and tree stem driven by the increasing NEE in spring‐early summer. Moreover, they highlighted a phenology‐dependent 15N fractionation during N transfer from ECM to their hosts. This evidence, obtained in mature beech trees under natural conditions, may improve the knowledge of Mediterranean forests functionality. Summary Statement: The natural abundances of C and N stable isotopes along the soil‐ectomycorrhiza‐plant continuum in mature Fagus sylvatica trees revealed the key role of ectomycorrhizae in regulating source‐sink relationships and the close interchange between biogeochemical cycles in forest ecosystem. [ABSTRACT FROM AUTHOR]

Food production is heavily dependent on soil phosphorus (P), a non-renewable mineral resource essential for plant growth and development. Alas, about 80% is unavailable for plant uptake. Arbuscular mycorrhizal fungi may promote soil P efficient use, although the mechanistic aspects are yet to be completely understood. In this study, plant and fungal variables involved in P acquisition were investigated in maize inbred lines, differing for mycorrhizal responsiveness and low-P tolerance, when inoculated with the symbiont Rhizoglomus irregulare (synonym Rhizophagus irregularis). The expression patterns of phosphate transporter (PT) genes in extraradical and intraradical mycelium (ERM/IRM) and in mycorrhizal and control maize roots were assessed, together with plant growth responses and ERM extent and structure. The diverse maize lines differed in plant and fungal accumulation patterns of PT transcripts, ERM phenotypic traits and plant performance. Mycorrhizal plants of the low-P tolerant maize line Mo17 displayed increased expression of roots and ERM PT genes, compared with the low-P susceptible line B73, which revealed larger ERM hyphal densities and interconnectedness. ERM structural traits showed significant correlations with plant/fungal expression levels of PT genes and mycorrhizal host benefit, suggesting that both structural and functional traits are differentially involved in the regulation of P foraging capacity in mycorrhizal networks. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) establish mutualistic associations with the most important agricultural food and feed crops, sustaining plant growth, nutrient uptake and tolerance of biotic and abiotic stresses. Scanty information is available on the role played by crop identity and diversity as a driving force shaping AMF species communities in the field, in particular in low-input and organic farming, where crop rotation and the use of cover crops are common practices. Here, using a molecular approach, we investigated whether plant communities established in low and high diversity cover crop treatments affect the composition of native AMF root communities of subsequent maize in a Mediterranean organic agroecosystem. A total of 16 AMF sequence types were detected, with Acaulospora cavernata as the most abundant phylotype, accounting for 37.4 % of the sequences, followed by Funneliformis mosseae, Claroideoglomus lamellosum and Rhizoglomus intraradices. Sequences matching to Funneliformis caledonium, Diversispora aurantia, Diversispora epigaea and Archaeospora schenckii corresponded to less than 2.0 % of the total. The most abundant sequences retrieved in plants from cover crop treatments were represented by A. cavernata, while sequences in maize roots were related to F. mosseae, R. intraradices and Glomus sp. Such data show for the first time a change in the composition of native AMF communities colonizing maize roots, which was independent of the identity and diversity of the preceding crop. Our findings suggest that host preference may represent a strong driver of AMF community dynamics in agroecosystems, differentially boosting or depressing AMF species, possibly in relation to their functional significance. [ABSTRACT FROM AUTHOR]

Experimental studies investigated the effects of transgenic crops on the structure, function and diversity of soil and rhizosphere microbial communities playing key roles in belowground environments. Here we review available data on direct, indirect and pleiotropic effects of engineered plants on soil microbiota, considering both the technology and the genetic construct utilized. Plants modified to express phytopathogen/phytoparasite resistance, or traits beneficial to food industries and consumers, differentially affected soil microorganisms depending on transformation events, experimental conditions and taxa analyzed. Future studies should address the development of harmonized methodologies by taking into account the complex interactions governing soil life. [ABSTRACT FROM AUTHOR]

The cultivation of GMPs in Europe raises many questions about the environmental risks, in particular about their ecological impact on non-target organisms and on soil properties. The aim of a multidisciplinary group engaged in a LIFE + project (MAN-GMP-ITA) was to validate and improve an existing environmental risk assessment (ERA) methodology on GMPs within the European legislative framework on GMOs. Given the impossibility of evaluating GMO impact directly, as GMPs are banned in Italy, GMPs have not been used at any stage of the project. The project thus specifically focused on the conditions for the implementation of ERA in different areas of Italy, with an emphasis on some sensitive and protected areas located in the North, Centre, and South of the country, in order to lay the necessary baseline for evaluating the possible effects of a GMP on soil communities. Our sub-group carried out soil analyses in order to obtain soil health and fertility indicators to be used as baselines in the ERA model. Using various methods of chemical, biochemical, functional and genetic analysis, our study assessed the changes in diversity and functionality of bacterial populations, and arbuscular mycorrhizal fungi. The results show that plant identity and growth, soil characteristics, and field site climatic parameters are key factors in contributing to variation in microbial community structure and diversity, thus validating our methodological approach. Our project has come to the conclusion that the uneven composition and biological-agronomical quality of soils need to be taken into consideration in a risk analysis within the framework of ERA for the release of genetically modified plants. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal (AM) symbioses affect plant competitive relationships within and among species and may be involved in the interactions among agricultural weed species and crops, depending on their mycorrhizal status. In this work, the impact of native AM fungi (AMF) on maize-weed(s) and weed-weed competitive relationships was assessed, using Solanum nigrum and Chenopodium album as model host and non-host weeds, respectively. Methods: Growth performance, nutrient use and competitive ability of crop and weed species were assessed in the pure stand and in different model plant communities of host and non-host species. Results: Results showed that maize performance decrease was more severe when grown with C. album than with S. nigrum. Differential responses to AMF occurred in the two weed species tested: mycorrhizal S. nigrum showed reduced biomass and N uptake when grown in competition with C. album. The negative performances observed when mycorrhizal S. nigrum grew in competition with C. album corresponded to C. album larger biomass production and N uptake. Conclusions: Results showed that AMF are able to alter the competitive relationships between co-occurring plant species differing in their mycorrhizal status (host/non-host), thus representing key soil organisms to be taken into account in sustainable weed management strategies. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs; nevertheless their spores can germinate in the absence of host plants. Such inconsistent behavior is balanced by diverse survival strategies. The ability of AM fungal hyphae to fuse might represent a fundamental survival strategy because germlings could plug into compatible mycorrhizal networks, thus gaining access to plant-derived carbon before asymbiotic growth arrest. An in vivo experimental system was used to grow extraradical mycelium produced by Glomus mosseae colonizing three different plant species and germlings of the same isolate. After symbiotic and asymbiotic mycelia came into contact we showed that germling hyphae fused with symbiotic network hyphae and established protoplasm connections with nuclei occurring in fusion bridges. The frequency of anastomoses between germling and symbiotic hyphae was 4.9-23.9%. Prefusion and postfusion incompatible responses, with protoplasm withdrawal in interacting hyphae, were evident in some hyphal contacts. Given the multigenomic nature of AMF, the mingling of germling nuclei with those of the mycorrhizal network through perfect fusions might represent a means for the maintenance of genetic diversity in the absence of sexual recombination. [ABSTRACT FROM AUTHOR]

In this work we have determined the community composition of spore-forming arbuscular mycorrhizal fungi (AMF) in a maquis site on Pianosa island, a protected area within the Tuscan Islands UNESCO Biosphere Reserve, Italy. We have analysed rhizosphere soil of the dominant plant species Pistacia lentiscus, Smilax aspera, Rosmarinus officinalis and of the endemic plant Helichrysum litoreum. The AMF species recovered were: Scutellospora dipurpurescens, Glomus coronatum, Glomus mosseae, Glomus etunicatum, Glomus geosporum, Glomus viscosum, Entrophospora sp ., Pacispora sp . and Glomus rubiforme. The identification of native S. dipurpurescens and G. coronatum was carried out on spores isolated from rhizosphere soil of H. litoreum, by combining morphological traits and 18S (SSU) and ITS rDNA sequences. Therefore, AMF species of Pianosa rhizosphere soils represent an important repository for the conservation and maintenance in their natural habitat of such beneficial symbionts, key microorganisms of soil fertility. [ABSTRACT FROM AUTHOR]

• The ability of arbuscular mycorrhizal (AM) networks originating from plants of different species, genera and families to become interconnected by means of hyphal anastomoses was assessed. • An in vivo two-dimensional experimental model system was used to reveal the occurrence of linkages between contiguous mycorrhizal networks spreading from Allium porrum root systems and those originating from Daucus carota, Gossypium hirsutum, Lactuca sativa, Solanum melongena, colonized by Glomus mosseae. • Percentages of hyphal contacts leading to anastomosis between extraradical networks originating from different plant species ranged from 44% in the pairing A. porrum– S. melongena to 49% in A. porrum– G. hirsutum. DAPI and Sytox stainings detected nuclei in the middle of fusion bridges connecting different mycorrhizal networks. • Present data suggest that, by means of anastomoses, AM fungal mycelium would potentially create an indefinitely large network interconnecting different plants in a community, and that, in the absence of sexual recombination, the intermingling of nuclei in extraradical mycelium may provide endless opportunities for the exchange of genetic material. © New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01145.x New Phytologist (2004) [ABSTRACT FROM AUTHOR]

We developed an experimental model system to monitor the impact of generically modified (GM) plants on arbuscular mycorrhizal (AM) fungi, a group of non-target soil microorganisms, fundamental for soil fertility and plant nutrition. The system allowed us to study the effects of root exudates of both commercialBtcorn and aubergine plants expressing Dm-AMP1 defensin on different stages of the life cycle of the AM fungal speciesG. mosseae. Root exudates ofBt176 corn significantly reduced pre-symbiotic hyphal growth, compared toBt11 and non-transgenic plants. No differences were found in mycelial growth in the presence of Dm-AMP1 and control plant root exudates. Differential hyphal morphogenesis occurred irrespective of the plant line, suggesting that both exudedBttoxin and defensin do not interfere with fungal host recognition mechanisms.Bt176 affected the regular development of appressoria, 36% of which failed to produce viable infection pegs. Our experimental model system represents an easy assay for testing the impact of GM plants on non-target soil-borne AM fungi. [ABSTRACT FROM AUTHOR]

We detected, for the first time, the occurrence of vegetative incompatibility between different isolates of the arbuscular mycorrhizal fungal species Glomus mosseae. Vegetative compatibility tests performed on germlings belonging to the same isolate showed that six geographically different isolates were capable of self-anastomosing, and that the percentage of hyphal contacts leading to fusions ranged from 60 to 85%. Successful anastomoses were characterized by complete fusion of hyphal walls, protoplasm continuity and occurrence of nuclei in the middle of hyphal bridges. No anastomoses could be detected between hyphae belonging to different isolates, which intersected without any reaction in 49 to 68% of contacts. Microscopic examinations detected hyphal incompatibility responses in diverse pairings, consisting of protoplasm retraction from the tips and septum formation in the approaching hyphae, even before physical contact with neighboring hyphae. Interestingly, many hyphal tips showed precontact tropism, suggesting that specific recognition signals may be involved during this stage. The intraspecific genetic diversity of G. mosseae revealed by vegetative compatibility tests was confirmed by total protein profiles and internal transcribed spacer-restriction fragment length polymorphism profiles, which evidenced a higher level of molecular diversity between the two European isolates IMA1 and BEG25 than between IMA1 and the two American isolates. Since arbuscular mycorrhizal fungi lack a tractable genetic system, vegetative compatibility tests may represent an easy assay for the detection of genetically different mycelia and an additional powerful tool for investigating the population structure and genetics of these obligate symbionts. [ABSTRACT FROM AUTHOR]

Isolation and physiological and molecular characterisation of culturable bacterial strains belonging to actinomycetes, pseudomonads and aerobic spore-forming bacteria were carried out on mycorrhizal root tips of Quercus robur var. peduncolata infected by Tuber borchii. Cellular density of the three bacterial groups in ectomycorrhizal root tips was estimated to be 1.3±0.11×106 cfu g−1 dry weight for total heterotrophic bacteria and 1.08±0.6×105 (mean±S.E.), 1.3±0.3×105 and 1.4±0.2×105 cfu g−1 dry weight for pseudomonads, actinomycetes and spore-forming bacteria respectively. Identification of pseudomonads by the Biolog® system indicated, besides the most represented species Pseudomonas fluorescens (biotypes B, F and G), the occurrence of strains belonging to Pseudomonas corrugata. Amplified ribosomal DNA restriction analysis of actinomycetes and spore formers revealed at least three and six different groups of patterns, respectively. Many bacterial isolates were able to induce variations in growth rates of T. borchii mycelium; among these, 101 strains showed antifungal activity, whereas 17 isolates, belonging to spore formers, were able to increase mycelial growth up to 78% when compared to uninoculated mycelial growth. The potential role of these populations in the development and establishment of mycorrhizas is discussed. [Copyright &y& Elsevier]

An experimental model for the study of recognition responses by arbuscular mycorrhizal symbionts to host roots was validated by analysing the main factors which might affect such responses. Results showed that fungal responses to host-derived signals were unaffected by the degree of sterility of the system, host age and mycorrhizal status, symbiont age, or different chemical and physical characteristics of hydrophilic membranes. Use of dialysis membranes showed that the molecules putatively eliciting fungal responses weigh less than 500 Da. Utilization of the model for studies of developmental expression of proteins and genes in arbuscular mycorrhizal symbionts is examined. [ABSTRACT FROM AUTHOR]

Tissue cultures of Nicotiana tabacum were utilized to investigate the mechanisms associated with host specificity and non-host incompatibility in mycorrhizal and pathogenic fungi. They were tested for expression of resistance to different species of mycorrhizal fungi and to a fungal pathogen of tobacco, Thielaviopsis basicola, by monitoring the production of callose, phenolic compounds and peroxidases in dual cultures. Tobacco cells reacted to the presence of all the mycorrhizal fungi with callose deposits, whereas callose was nearly always absent in tobacco cells inoculated with their pathogen T. basicola. The broad-host range ectomycorrhizal fungi Hebeloma crustuliniforme, Laccaria laccata and Suillus granulatus elicited less intense responses than did Hymenoscyphus ericae. The results obtained for phenolic production and peroxidase activity were consistently similar to those obtained for callose deposition. They showed that H. ericae, an endomycorrhizal symbiont of Ericaceae, was highly incompatible with tobacco cells and that the tobacco pathogen T. basicola did not elicit strong reactions in the cells of its host. In this paper, the possibility of utilizing callus cultures as a simple model system to study both the different degrees of compatibility and the early events of recognition between mycorrhizal fungi and their host or non-host plants is discussed. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the course of fungal growth of Glomus caledonium, from spore germination to growth arrest of arbuscular mycorrhizal sumbionts in the absence of the host and examined the metabolic activity of the fungus after growth arrest. Details on the cell events involved in developmental arrest; Information on the hyphal growth of the fungus; Metabolic activity and infectivity of the fungus; Results of the study.

Arbuscular mycorrhizal fungi (AMF) are a key group of beneficial obligate biotrophs, establishing a mutualistic symbiosis with the roots of most land plants. The molecular markers generally used for their characterization are mainly based on informative regions of nuclear rDNA (SSU-ITS-LSU), although protein-encoding genes have also been proposed. Within functional genes, those encoding for phosphate transporters (PT) are particularly important in AMF, given their primary ability to take up Pi from soil, and to differentially affect plant phosphate nutrition. In this work, we investigated the genetic diversity of PT1 gene sequences and sequences of the taxonomically relevant SSU-ITS-LSU region in two isolates of the species Funneliformis coronatus , three isolates of the species Funneliformis mosseae and two species of the genus Rhizoglomus , originated from geographically distant areas and cultured in vivo. Our results showed that partial PT1 sequences not only successfully differentiated AMF genera and species like ribosomal gene sequences but also highlighted intraspecific diversity among F. mosseae and F. coronatus isolates. The study of functional genes related to the uptake of key mineral nutrients for the assessment of AMF diversity represents a key step in the selection of efficient isolates to be used as inocula in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Positive effects of arbuscular mycorrhizal fungi (AMF)—wheat plant symbiosis have been well discussed by research, while the actual role of the single wheat genotype in establishing this type of association is still poorly investigated. In this work, the genetic diversity of Triticum turgidum wheats was exploited to detect roots susceptibility to AMF and to identify genetic markers in linkage with chromosome regions involved in this symbiosis. A tetraploid wheat collection of 127 accessions was genotyped using 35K single-nucleotide polymorphism (SNP) array and inoculated with the AMF species Funneliformis mosseae (F. mosseae) and Rhizoglomus irregulare (R. irregulare), and a genome‐wide association study (GWAS) was conducted. Six clusters of genetically related accessions were identified, showing a different mycorrhizal colonization among them. GWAS revealed four significant quantitative trait nucleotides (QTNs) involved in mycorrhizal symbiosis, located on chromosomes 1A, 2A, 2B and 6A. The results of this work enrich future breeding activities aimed at developing new grains on the basis of genetic diversity on low or high susceptibility to mycorrhization, and, possibly, maximizing the symbiotic effects. [ABSTRACT FROM AUTHOR]

Purpose: Commercial production and the use of liquid vermicompost extract (LVE) is gaining attention as a technique that supports integrated soil-microbial-crop management for sustainable agriculture. However, the interaction effects of LVE, arbuscular mycorrhizal fungi (AMF), and host plants on the delivery of agroecosystem services in alkaline soil have been less studied. Methods: We carried out a 3-year field experiment in Central Italy, to investigate the short-term effect of LVE on soil mycorrhizal inoculum potential (MIP), AMF root colonization, and productivity of berseem clover, lentil, and sunflower. LVE produced in different years were screened for microbial properties using Illumina Miseq sequencing. LVE was applied at seeding, crop stem elongation and flowering stages. Control crops received water as a placebo. Results: LVE bacterial communities were more diverse and showed a higher turnover between 2019 and 2020 than fungal communities. Diverse microbial groups, the majority of which belonged to phyla Proteobacteria, Bacteroidetes, Firmicutes, and Mucoromycota, were detected, including N-fixers (Flavobacterium, Malikia, and Citrobacter), P-solubilizers (Pseudomonas), and C-degraders (Tolumonas, Arcobacter, and Mucor). Notably, LVE treatment enhanced soil MIP and AMF root colonization in most crops, but selectively improved shoot biomass of berseem clover (+ 32%) and sunflower (+ 34%), and grain yield (+ 37%) and oil concentration (+ 5%) in sunflower, compared to the corresponding non-treated controls. Conclusions: LVE had diverse groups of bacteria and a few fungal taxa, and its application enhanced mycorrhizal properties and selected growth- and yield-related variables in lentil, berseem clover, and sunflower. This could be due to LVE's biostimulating effect arising from the vermicompost-associated microbiome and biomolecules. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi are increasingly used in organic cropping systems to increase yields. Although cover crops are largely used in organic farming, there is little knowledge on the impact of cover crops on native mycorrhizal fungi. Here, we studied the effect of cover crop diversity on mycorrhizal colonization in subsequent organic maize cultivars differing in the level of genetic diversity. Experiments were conducted from 2010 to 2012 in a Mediterranean environment. First Indian mustard ( Brassica juncea L. Czern.), hairy vetch ( Vicia villosa Roth), a mix of seven cover crop species (Mix), and natural vegetation (Control) were cultivated as winter cover crops. Then, an organically and a conventionally bred maize hybrid and three organically bred composite cross populations were cultivated. Mycorrhizal propagule dynamics were measured. Results at juvenile stage show a higher mycorrhizal colonization in maize plants grown after hairy vetch, of 35.0 %, and Mix cover crops, of 29.4 %, compared to Indian mustard, of 20.9 %, and Control, of 21.3 %. The potential of soil mycorrhization decreased of 56.5 % following Indian mustard, higher than that of other cover crops, of 34.1-47.3 %. This finding could be explained by the release of isothiocyanates in soils. Moreover, maize shoot biomass, nitrogen, and phosphorus content across all maize genotypes at juvenile stage increased with mycorrhizal colonization. These findings provide the first evidence of the greater role played by cover crop identity in the enhancement of early mycorrhizal colonization of the subsequent crop and of soil mycorrhizal activity. [ABSTRACT FROM AUTHOR]

• AMF outperforms phosphate in favouring nutrient uptake. • AMF boosts photosynthesis & secondary metabolism. • Transcriptome analysis reveals molecular bases of several AMF effects. • AMF triggers distinct gene expression compared to phosphate. • Gene expression correlates with plant traits. Lettuce (Lactuca sativa L.) is an annual autogamous diploid plant belonging to Asteraceae and is among the top ten most profitable crops worldwide due to its nutritional value. Nevertheless, lettuce is an intensive crop with high input demand, especially fertilisers, both in soil-bound and soilless culture, with negative impact on the environment and production costs. In this context, arbuscular mycorrhizal symbioses could help to reduce the impact of fertilisers, improving plant nutrition, particularly regarding phosphorus, and contributing to growing healthier plants for human consumption. In our work, we compared lettuce plants (cv. Salinas) grown in soilless culture with optimal phosphorus concentration in the nutrient solution, with sub-optimal phosphorus nutrition and with plants grown with sub-optimal phosphorus concentration and inoculated with the fungus Funneliformis mosseae before transplanting. Higher levels of primary and secondary metabolites along with increased biomass were observed for mycorrhizal plants compared to lettuces grown with optimal and sub-optimal concentrations of phosphate. Gene expression profile was analysed in both roots and leaves, and transcriptomic values were associated with growth and biochemical parameters. Three-thousand and fifty-seven genes were differentially regulated by mycorrhizal symbiosis and 2,606 genes by optimal phosphate nutrition. Different genes related to photosynthesis, solute transport, metabolism of phytohormones, redox homeostasis, and transcriptional regulation resulted differentially regulated between culture conditions. Mycorrhizal plants also boosted the activation of genes involved in phenylpropanoids and carotenoids metabolism. In conclusion, growth, biochemical, and transcriptomic data show that symbiotic plants benefit both plant growth and leaf content of health promoting phytochemicals through genetic pathways that largely differed those activated in plants grown with optimal phosphorus supply. [ABSTRACT FROM AUTHOR]

In organic agriculture, soil fertility and productivity rely on biological processes carried out by soil microbes, which represent the key elements of agroecosystem functioning. Arbuscular mycorrhizal fungi (AMF), fundamental microorganisms for soil fertility, plant nutrition and health, may play an important role in organic agriculture by compensating for the reduced use of fertilizers and pesticides. Though, AMF activity and diversity following conversion from conventional to organic farming are poorly investigated. Here we studied AMF abundance, diversity and activity in short- and long-term organically and conventionally managed Mediterranean arable agroecosystems. Our results show that both AMF population activity, as assessed by the mycorrhizal inoculum potential (MIP) assay, the percentage of colonized root length of the field crop (maize) and glomalin-related soil protein (GRSP) content were higher in organically managed fields and increased with time since transition to organic farming. Here, we showed an increase of GRSP content in arable organic systems and a strong correlation with soil MIP values. The analysis of AMF spores showed differences among communities of the three microagroecosystems in terms of species richness and composition as suggested by a multivariate analysis. All our data indicate that AMF respond positively to the transition to organic farming by a progressive enhancement of their activity that seems independent from the species richness of the AMF communities. Our study contributes to the understanding of the effects of agricultural managements on AMF, which represent a promising tool for the implementation of sustainable agriculture. [ABSTRACT FROM AUTHOR]

Abstract: The effect of different sulphur dioxide concentrations on culturability and viability of seven strains of Brettanomyces bruxellensis was tested in a synthetic wine medium (SWM) and a different response to molecular SO2 among strains was detected. Sulphur dioxide induced a viable but non culturable (VBNC) state in all the strains. The greater percentage of VBNC cells were identified for five strains at molecular SO2 concentrations of 0.2mg/L and for two strains at the concentration of 0.4mg/L. Vinyl phenols were detected in media containing VBNC or not viable B. bruxellensis, suggesting that its spoilage metabolism could be maintained during wine storage. Overall, this study indicates that SO2 is a chemical stressor inducing VBNC state in B. bruxellensis grown in synthetic wine medium. Further studies are needed to evaluate the effects of SO2 on the metabolism of this yeast in wine spoilage. [ABSTRACT FROM AUTHOR]

Investigation on the lace of appressorium formation in the roots of the non-host plant Lupinus albus L. showed that root exudates do no inhibit mycelial growth of the vesicular arbuscular mycorrhizal (VAM) fungus Glomus mosseae (NicaL & Gerd.) Gerd. & Trappe, but that they hinder hyphal attachment and fungal recognition of roots. Exudates do not stimulate hyphal proliferation in the rhizosphee. G. masseae hyphae were able to recognize and attach to excised roots of both lupin and host plants, forming swellings resembling appressoria. no growth of G. mosseae hyphae was observed around simulated roots consisting of nylon, silk, polyamide and glass threads, whereas uppressoria were formed on heterologous hyphae of VAM fungal species. The hypothesis that a purely thigmotropic stimulus could trigger hyphal attachment and the further differentiation of appressoria was excluded. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) play a key role in plant nutrition and in the maintenance of soil fertility in agroecosystems, but their survival can be affected by different agricultural practices, including the use of pesticides. In this work, we assessed the impact of chemicals with herbicidal and fungicidal activity on mycelial growth and structure of the worldwide distributed AMF Funneliformis mosseae. Results showed that mycelial growth and interconnectedness of three different F. mosseae lineages were affected by the chemicals tested at concentrations lower than those indicated for agricultural use. Indeed, benomyl reduced mycelial growth in one lineage and fenhexamid negatively affected germlings growth in the three lineages, while both fungicides significantly affected mycelial viability and induced abnormal hyphal branching. The three F. mosseae lineages showed sensitivity to herbicides, with significant growth and viability decreases in the presence of the active ingredient glufosinate ammonium and a low viability at increasing concentrations of dicamba. Anastomosis rates were reduced by the two fungicides and by very low levels of the herbicide glufosinate, whose impact on AMF networks should be further investigated, given its wide use in agriculture. Our results suggest that the use of some pesticides in agroecosystems may lead to growth reduction and disruption of AMF mycelial structural traits, even in AMF species able to tolerate soil disturbance, posing serious threats to AMF symbiotic performance and to the maintenance of soil mycorrhizal potential. • Fungicides affect mycelial growth and viability of arbuscular mycorrhizal fungi. • Mycelial interconnectedness of arbuscular mycorrhizal fungi is reduced by fungicides. • The herbicide glufosinate decreases mycelial growth and interconnectedness. [ABSTRACT FROM AUTHOR]

Retrotransposon expression during arbuscular mycorrhizal (AM) fungal colonisation of sunflower roots (Helianthus annuus) was analysed using Illumina RNA-Seq, in order to verify whether mycorrhizal symbiosis can activate retrotransposable elements. Illumina cDNA libraries were produced from RNAs isolated from the roots of sunflower plants at 4 and 16 days after inoculation with the AM fungus Rhizoglomus irregulare and from their respective control plants. Illumina reads were mapped to a library of reverse transcriptase-encoding sequences, putatively belonging to long terminal repeat retrotransposons of Gypsy and Copia superfamilies. Forty-six different reverse transcriptase sequences were transcribed, although at a low rate, in mycorrhizal or control roots and only four were significantly over-expressed at day 16, compared with control roots. Almost all expressed or over-expressed sequences belonged to low-copy elements, mostly, of the Copia superfamily. A meta-analysis, using publicly available Illumina cDNA libraries obtained from sunflower plants treated with different hormones and chemicals, mimicking stimuli produced by abiotic and biotic stresses, was also conducted. Such analyses indicated that the four reverse transcriptase sequences over-expressed in mycorrhizal roots were explicitly induced only by AM symbiosis, showing the specificity of AM stimuli compared to that of other fungal/plant interactions. [ABSTRACT FROM AUTHOR]

In intercropping systems, crop species select host-adapted microorganisms and influence the associated plant-microbial interactions like in the case of arbuscular mycorrhizal fungi (AMF). Attempts to assess the impact of intercropping on the activity, diversity, and community composition of AMF remain inconclusive, more so in intercropping systems involving traditional Mediterranean crops such as durum wheat and lentils. We carried out field experiments in Central Italy to assess the impact of relay intercropping durum wheat (Triticum durum Desf. cv. Minosse) and lentil (Lens culinaris Medik. cv. Elsa) on soil mycorrhizal inoculum potential (MIP) (2019 and 2020), AMF root colonization (2019, 2020, and 2021), and root AMF diversity and community composition (2020 and 2021), compared to the respective sole crops. Results showed that relay intercropping enhanced lentil grain yield and durum wheat grain protein concentration but marginally reduced durum wheat grain yield and lentil grain protein concentration. In addition, relay intercropping enhanced soil mycorrhizal activity but differentially influenced mycorrhizal root colonization compared to sole cropping. Sequencing analyses generated a total of 234 amplicon sequence variants belonging to Glomeromycota, which were assigned to 31 virtual taxa using the MaarjAM reference database. Glomeraceae and Claroideoglomeraceae were the most abundant taxa but had contrasting abundances in 2020 and 2021. The overall changes in AMF species diversity and community structure were affected by the interaction between crop species and year, and not by intercropping. Claroideoglomus and Septoglomus showed a strong association with lentil roots while Rhizophagus and Paraglomus were associated with durum wheat roots in 2020, affirming host genotype-AMF preferences. The principal component analysis showed that grain protein concentration was associated with selected mycorrhizal parameters such as community richness and AMF root colonization. Further studies on the functional analysis of the different AMF communities selected by the crop genotype and year may reveal the importance of intercropping in maintaining soil functionality and productivity under low-input systems. • Relay intercropping influences plant and soil-microbial interactions. • Relay intercropping favored lentil grain production and durum wheat grain protein quality. • Durum wheat-lentil relay intercropping enhanced soil mycorrhizal activity. • Durum wheat-lentil relay intercropping did not alter structure of AMF community within roots. • AMF community richness was associated with durum wheat grain protein concentration. [ABSTRACT FROM AUTHOR]

Intact whole native AMF communities occurring across a 100-m-long field were used for the evaluation of plant performance, as determined by the actual fungal species colonizing host roots. The soil from distinct plots within a 'hot spot' field was collected to set up 54 experimental units where three different plant species were grown, in order to test whether the whole native AMF communities were able to differentially affect plant growth, to assess the genetic identity of the AMF actually colonizing the tested plants and to analyse their community composition in the different hosts. Molecular analyses revealed that plant growth and nutrition of the crop plants were differentially affected by the diverse native arbuscular mycorrhizal communities colonizing the roots of the three plants, whose performance varied depending on the identity of plant hosts and fungal symbionts, more than on a rich and diversified AMF community. Such results, improving our understanding of AMF distribution at the local scale, represent a starting point allowing the selection, isolation and characterization of the most efficient AMF assemblages to be used as inoculants in sustainable food production systems. [ABSTRACT FROM AUTHOR]

The increasing demand for products based from Stevia rebaudiana Bertoni (both leaves and purified steviol glycosides) makes of interest the research on sustainable production systems, in order to guarantee secure availability and high quality of agricultural raw materials. Arbuscular mycorrhizal fungi (AMF) symbiosis represents an interesting tool for increasing crop production and quality, especially thanks to improved nutrient absorption, particularly phosphorus (P). In the present study, Stevia rebaudiana Bert. plants were exposed to different levels of P fertilization (0, 25 and 50 mg P 2 O 5 kg −1 soil) with or without Rhizoglomus irregulare inoculation, in order to evaluate root colonization, plant growth and productive parameters, steviol glycosides (SVglys) yield, as well as nitrogen (N) and P concentrations and uptake. A nutrient balance was also carried out and the nutrient use efficiency was evaluated. Stevia roots were highly colonized by Rhizoglomus irregulare , especially in the absence of P fertilization. During the whole vegetative growth, the AMF symbiosis, in association with the P supply, benefitted stevia growth, especially with regard to leaf dry biomass production and SVglys yield. Arbuscular mycorrhizal fungi symbiosis was able to modify the growth habit of stevia plants, with increased branching and a reduced plant height. At the end of the vegetative growth, mycorrhizal plants reached the highest leaf dry yield, together with the highest SVglys production. The application of 25 mg P 2 O 5 kg −1 soil in association with AMF symbiosis seemed to be the most effective treatment in improving stevia SVglys yield and P uptake together with P nutrient use efficiency. [ABSTRACT FROM AUTHOR]

Beneficial soil biota, and in particular, arbuscular mycorrhizal fungi (AMF) are increasingly being recognized as key elements of organic and low-input agriculture where agrobiodiversity is central to enhanced crop production. However, the role of AMF in diversified organic systems, especially in field crops, is still poorly understood. A 3-year field experiment was carried out in Central Italy to investigate whether organic cropping systems that promote species and genetic diversity are more prone to mycorrhizal symbiosis increasing tomato growth, production and yield quality. Three tomato cultivars with varying genetic diversity were grown following four cover treatments: Indian mustard ( Brassica juncea L. Czern.), hairy vetch ( Vicia villosa Roth), a commercial mixture of seven cover crop species (Mix 7) and no-till fallow. Plants were either inoculated or not in nursery, with the two AMF isolates Funneliformis mosseae (IMA1) and Rhizoglomus intraradices (IMA6) used alone or mixed in a 1:1 volume ratio. On average, Mix 7 produced higher shoot dry matter (5.0 t ha −1 ) than V. villosa (3.5 t ha −1 ) or B. juncea (2.5 t ha −1 ). Pre-transplant inoculation increased tomato root colonization at flowering and harvest compared to the non inoculated plants (31.8 vs 23.6%) and cv. Rio Grande was on average the best colonized. The mean fresh weight of marketable fruits was 18.4, 28.0 and 28.6 t ha −1 for cvs. Rio Grande, Roma and Perfect Peel, respectively. Cover crops inconsistently affected tomato marketable fruit production in year 1, while in years 2 and 3, Vicia villosa and Mix 7 showed the best effect respectively. In year 3, among the pre-inoculated plants those treated with isolate IMA6 showed a higher production of marketable fruit number m −2 (56.7) than those inoculated either with IMA1 (51.5) or the mixed inocula (52.1). Most fruit quality parameters were affected by tomato genotype. This study shows that while increased agrobiodiversity is important to increase agroecosystem resilience, AMF, crop and cover crop functional identity may be more important than diversity per se to promote mycorrhizal symbiosis and productivity of field grown organic tomato. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungal (AMF) communities are fundamental in organic cropping systems where they provide essential agro-ecosystem services, improving soil fertility and sustaining crop production. They are affected by agronomic practices, but still, scanty information is available about the role of specific crops, crop rotations and the use of winter cover crops on the AMF community compositions at the field sites. A field experiment was conducted to elucidate the role of diversified cover crops and AMF inoculation on AMF diversity in organic tomato. Tomato, pre-inoculated at nursery with two AMF isolates, was grown following four cover crop treatments: Indian mustard, hairy vetch, a mixture of seven species and a fallow. Tomato root colonization at flowering was more affected by AMF pre-transplant inoculation than by the cover crop treatments. An enormous species richness was found by morphological spore identification: 58 AMF species belonging to 14 genera, with 46 and 53 species retrieved at the end of cover crop cycle and at tomato harvest, respectively. At both sampling times, AMF spore abundance was highest in hairy vetch, but after tomato harvest, AMF species richness and diversity were lower in hairy vetch than in the cover crop mixture and in the mustard treatments. A higher AMF diversity was found at tomato harvest, compared with the end of the cover crop cycle, independent of the cover crop and pre-transplant AMF inoculation. Our findings suggest that seasonal and environmental factors play a major role on AMF abundance and diversity than short-term agronomic practices, including AMF inoculation. The huge AMF diversity is explained by the field history and the Mediterranean environment, where species characteristic of temperate and sub-tropical climates co-occur. [ABSTRACT FROM AUTHOR]

Abstract: The impact of nitrogen (N) fertilization and tillage on arbuscular mycorrhizal fungi (AMF) was studied in a Mediterranean arable system by combining molecular, biochemical and morphological analyses of field soil and of soil and roots from trap plants grown in microcosm. Canonical correspondence analysis (CCA) of PCR–DGGE banding patterns evidenced that AMF communities in the field are affected by N-fertilization and tillage. N-fertilization was also the main factor shaping AMF communities in Medicago sativa trap plant soil and roots. The overall sporulation pattern of the different AMF species showed a predominant effect of tillage on AMF communities, as shown by CCA analysis. Funneliformis mosseae was the predominant species sporulating in tilled soils, while Glomus viscosum and Glomus intraradices prevailed in no-tilled soils. Field glomalin-related soil protein content was reduced by tillage practices. Our multimodal approach, providing data on two main production factors affecting soil AMF communities, may help implementing effective agricultural management strategies able to support the beneficial relationship between crops and native AMF symbionts. [Copyright &y& Elsevier]

Greenhouse and field experiments were carried out in order to investigate the influence of mycorrhizal inoculation on total phenolic content (TPC) and antioxidant activity, expressed as antiradical power (ARP), of artichoke ( Cynara cardunculus L. var. scolymus F.) leaves and flower heads extracts. The establishment of mycorrhizal symbiosis was monitored in pot and field grown plants, and the persistence of the inoculated AMF in roots after 2 years’ growth in the field was assessed by fungal ITS sequencing. Both in the greenhouse and in the field, marked increases in TPC and ARP were detected in leaves and flower heads of artichoke plants inoculated with the AM fungal species Glomus intraradices, either alone or in mixture with Glomus mosseae. In the field, plants inoculated with Glomus mix showed flower heads ARP content increases of 52.7 and 30.0% in the first and second year, respectively, compared with uninoculated plants. After 2 years’ growth in the field ITS rDNA sequences clustering with those of G. mosseae and G. intraradices were retrieved only from inoculated plant roots. Our data show that mycorrhizal inoculation may represent an efficient and sustainable strategy to improve productivity and enhance plant biosynthesis of secondary metabolites with health promoting activities. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhizal fungi (AMF) form symbioses with the majority of plants and form extensive underground hyphal networks simultaneously connecting the roots of different plant species. No empirical evidence exists for either anastomosis between genetically different AMF or genetic exchange. • Five isolates of one population of Glomus intraradices were used to study anastomosis between hyphae of germinating spores. We show that genetically distinct AMF, from the same field, anastomose, resulting in viable cytoplasmic connections through which genetic exchange could potentially occur. • Pairs of genetically different isolates were then co-cultured in an in vitro system. Freshly produced spores were individually germinated to establish new cultures. Using several molecular tools, we show that genetic exchange occurred between genetically different AMF. Specific genetic markers from each parent were transmitted to the progeny. The progeny were viable, forming symbioses with plant roots. The phenotypes of some of the progeny were significantly different from either parent. • Our results indicate that considerable promiscuity could occur in these fungi because nine out of 10 combinations of different isolates anastomosed. The ability to perform genetic crosses between AMF experimentally lays a foundation for understanding the genetics and evolutionary biology of these important plant symbionts. [ABSTRACT FROM AUTHOR]

The concept of food quality, traditionally based on nutritional and sensory properties, has recently acquired an additional meaning, referring to the health-promoting properties of plant products, that are ascribed to plant secondary metabolites called phytochemicals, primarily represented by polyphenolic compounds and glucosinolates. The diversity and content of phytochemicals in plant products are affected by different variables, such as plant genotype, agronomic factors, and arbuscular mycorrhizal fungi (AMF), which establish mycorrhizal symbioses with most crops, including cereals, legumes, vegetables, fruit trees, sunflower, cotton, and sugarcane. AMF and associated bacteria enhance plant growth and health, and affect the production of polyphenols and carotenoids, and the activity of antioxidant enzymes. The production of health-promoting phytochemicals was shown to be differentially modulated by different AMF isolates and bacterial strains, in several food plants, i.e., tomato, lettuce, strawberry, artichoke, maize, grapevine, sunflower. Here, we provide an overview of recent studies concerning the multiple roles played by AMF and associated bacteria in the modulation of the biosynthesis of plant secondary metabolites with health-promoting activity, and discuss the development of designed multifunctional consortia to be used in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) establish mutualistic symbioses with the roots of most plant species, playing a key role in crop productivity and ecosystem functioning. The characterization of local AMF genotypes assemblages is a prerequisite for the reproduction, both ex situ and on farm, of efficient native AMF communities, in order to improve soil quality and fertility through agricultural management and to use selected AMF as inoculants in sustainable agriculture. Contrasting evidences have been found by studies addressing the influence of different environmental drivers, among which geographical distance, on the diversity and composition of AMF communities in agricultural soils. In the present study, a Mediterranean "hot-spot" of AMF species richness was studied to assess whether AMF display a spatial structure at a local scale and whether their spore distribution is affected by soil variables. AMF distribution patterns were estimated by spore analysis, in 12 field plots, which were characterized for their chemical and physical variables. Plots were distributed along a transect across the field, and sampling points distances ranged from 4 to 102 m. While most taxa displayed an aggregated distribution, no significant spatial correlation was detected among AMF communities. On the contrary, AMF communities were significantly correlated with the entire set of soil variables, and with distinct soil characteristics, such as pH and total N, but not P. Among the most abundant taxa, Funneliformis geosporus , Septoglomus constrictum , Funneliformis mosseae , Ambispora granatensis and Glomus badium , were positively affected by total N, and Paraglomus occultum negatively affected by pH. Multiple regression analysis revealed that distribution of most AMF species was significantly related to nitrogen, clay, cation exchange capacity and pH. Multivariate (RDA) analysis confirmed results of multiple regression, with the best model selecting three soil variables (N, clay and pH). Variance partitioning analysis also showed that AMF distribution was mostly explained by environmental variables (36.4%) and by environmental variables spatial structure (16.4%). Overall, the results of this work revealed the importance of soil variables in shaping AMF community composition and spatial heterogeneity, within a site characterized by high AMF richness. • Soil variables shape AMF spore community composition and spatial heterogeneity. • AMF community composition significantly correlates with the entire set of soil variables. • Most abundant AMF species are positively affected by soil N, clay, CEC and pH. • Paraglomus occultum is negatively affected by soil pH. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are beneficial soil microorganisms establishing mutualistic symbioses with the roots of the most important food crops and playing key roles in the maintenance of long-term soil fertility and health. The great inter- and intra-specific AMF diversity can be fully exploited by selecting AMF inocula on the basis of their colonization ability and efficiency, which are affected by fungal and plant genotypes and diverse environmental variables. The multiple services provided by AMF are the result of the synergistic activities of the bacterial communities living in the mycorrhizosphere, encompassing nitrogen fixation, P solubilization, and the production of phytohormones, siderophores, and antibiotics. The tripartite association among host plants, mycorrhizal symbionts, and associated bacteria show beneficial emerging properties which could be efficiently exploited in sustainable agriculture. Further in-depth studies, both in microcosms and in the field, performed on different AMF species and isolates, should evaluate their colonization ability, efficiency, and resilience. Transcriptomic studies can reveal the expression levels of nutrient transporter genes in fungal absorbing hyphae in the presence of selected bacterial strains. Eventually, newly designed multifunctional microbial consortia can be utilized as biofertilizers and biostimulants in sustainable and innovative production systems. [ABSTRACT FROM AUTHOR]