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Arbuscular mycorrhizal fungi (AMF) play a crucial role in enhancing plant growth, but their use in agriculture is limited due to several constraints. Elevated soil phosphate levels resulting from fertilization practices strongly inhibit fungal development and reduce mycorrhizal growth response. Here, we investigated the possibility of adapting Rhizoglomus irregulare to high phosphate (Pi) levels to improve its tolerance. A fungal inoculum was produced through multiple generations in the presence of elevated Pi and used to inoculate melon plants grown under low and high phosphate conditions. Our results revealed distinct phenotypic and transcriptomic profiles between the adapted and non-adapted Rhizoglomus irregulare. The Pi adapted phenotype led to enhanced root colonization under high Pi conditions, increased vesicle abundance, and higher plant biomass at both phosphate levels. Additionally, the adaptation status influenced the expression of several genes involved in Pi uptake, Pi signaling, and mitochondrial respiration in both symbiotic partners. While the underlying mechanisms of the adaptation process require further investigation, our study raises intriguing questions. Do naturally occurring phosphate-tolerant AMF already exist? How might the production and use of artificially produced inocula bias our understanding? Our findings shed light on the adaptive capacities of Glomeromycota and challenge previous models suggesting that plants control mycorrhizal fungal growth. Moreover, our work pave the way for the development of innovative biotechnological tools to enhance the efficacy of mycorrhizal inoculum products under practical conditions with high phosphate fertilization. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) play a crucial role in enhancing plant growth, but their use in agriculture is limited due to several constraints. Elevated soil phosphate levels resulting from fertilization practices strongly inhibit fungal development and reduce mycorrhizal growth response. Here, we investigated the possibility of adapting Rhizoglomus irregulare to high phosphate (Pi) levels to improve its tolerance. A fungal inoculum was produced through multiple generations in the presence of elevated Pi and used to inoculate melon plants grown under low and high phosphate conditions. Our results revealed distinct phenotypic and transcriptomic profiles between the adapted and non-adapted Rhizoglomus irregulare. The Pi adapted phenotype led to enhanced root colonization under high Pi conditions, increased vesicle abundance, and higher plant biomass at both phosphate levels. Additionally, the adaptation status influenced the expression of several genes involved in Pi uptake, Pi signaling, and mitochondrial respiration in both symbiotic partners. While the underlying mechanisms of the adaptation process require further investigation, our study raises intriguing questions. Do naturally occurring phosphate-tolerant AMF already exist? How might the production and use of artificially produced inocula bias our understanding? Our findings shed light on the adaptive capacities of Glomeromycota and challenge previous models suggesting that plants control mycorrhizal fungal growth. Moreover, our work pave the way for the development of innovative biotechnological tools to enhance the efficacy of mycorrhizal inoculum products under practical conditions with high phosphate fertilization.

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Main conclusion: Tomato plant acclimation to a mild water stress implied tissue-specific hormonal and nutrient adjustments, being the root one of the main modulators of this response. Phytohormones are key regulators of plant acclimation to water stress. However, it is not yet clear if these hormonal responses follow specific patterns depending on the plant tissue. In this study, we evaluated the organ-specific physiological and hormonal responses to a 14 day-long mild water stress in tomato plants (Solanum lycopersicum cv. Moneymaker) in the presence or absence of the arbuscular mycorrhizal fungus Rhizoglomus irregulare, a frequently used microorganism in agriculture. Several physiological, production, and nutritional parameters were evaluated throughout the experiments. Additionally, endogenous hormone levels in roots, leaves, and fruits at different developmental stages were quantified by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC–MS/MS). Water deficit drastically reduced shoot growth, while it did not affect fruit production. In contrast, fruit production was enhanced by mycorrhization regardless of the water treatment. The main tissue affected by water stress was the root system, where huge rearrangements in different nutrients and stress-related and growth hormones took place. Abscisic acid content increased in every tissue and fruit developmental stage, suggesting a systemic response to drought. On the other hand, jasmonate and cytokinin levels were generally reduced upon water stress, although this response was dependent on the tissue and the hormonal form. Finally, mycorrhization improved plant nutritional status content of certain macro and microelements, specially at the roots and ripe fruits, while it affected jasmonate response in the roots. Altogether, our results suggest a complex response to drought that consists in systemic and local combined hormonal and nutrient responses. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are non-coding small RNAs that play crucial roles in plant development and stress responses and can regulate plant interactions with beneficial soil microorganisms such as arbuscular mycorrhizal fungi (AMF). To determine if root inoculation with distinct AMF species affected miRNA expression in grapevines subjected to high temperatures, RNA-seq was conducted in leaves of grapevines inoculated with either Rhizoglomus irregulare or Funneliformis mosseae and exposed to a high-temperature treatment (HTT) of 40 °C for 4 h per day for one week. Our results showed that mycorrhizal inoculation resulted in a better plant physiological response to HTT. Amongst the 195 identified miRNAs, 83 were considered isomiRs, suggesting that isomiRs can be biologically functional in plants. The number of differentially expressed miRNAs between temperatures was higher in mycorrhizal (28) than in non-inoculated plants (17). Several miR396 family members, which target homeobox-leucine zipper proteins, were only upregulated by HTT in mycorrhizal plants. Predicted targets of HTT-induced miRNAs in mycorrhizal plants queried to STRING DB formed networks for Cox complex, and growth and stress-related transcription factors such as SQUAMOSA promoter-binding-like-proteins, homeobox-leucine zipper proteins and auxin receptors. A further cluster related to DNA polymerase was found in R. irregulare inoculated plants. The results presented herein provide new insights into miRNA regulation in mycorrhizal grapevines under heat stress and can be the basis for functional studies of plant-AMF-stress interactions. [ABSTRACT FROM AUTHOR]

Co-inoculation of arbuscular mycorrhizal fungi (AMF) and bacteria can synergically and potentially increase nitrogen use efficiency (NUE) in plants, thus, reducing nitrogen (N) fertilizers use and their environmental impact. However, limited research is available on AMF-bacteria interaction, and the definition of synergisms or antagonistic effects is unexplored. In this study, we adopted a response surface methodology (RSM) to assess the optimal combination of AMF (Rhizoglomus irregulare and Funneliformis mosseae) and Bacillus megaterium (a PGPR--plant growth promoting rhizobacteria) formulations to maximize agronomical and chemical parameters linked to N utilization in maize (Zea mays L.). The fitted mathematical models, and also 3D response surface and contour plots, allowed us to determine the optimal AMF and bacterial doses, which are approximately accorded to 2.1 kg ha-1 of both formulations. These levels provided the maximum values of SPAD, aspartate, and glutamate. On the contrary, agronomic parameters were not affected, except for the nitrogen harvest index (NHI), which was slightly affected (pvalue of < 0.10) and indicated a higher N accumulation in grain following inoculation with 4.1 and 0.1 kg ha-1 of AMF and B. megaterium, respectively. Nonetheless, the identification of the saddle points for asparagine and the tendency to differently allocate N when AMF or PGPR were used alone, pointed out the complexity of microorganism interaction and suggests the need for further investigations aimed at unraveling the mechanisms underlying this symbiosis. [ABSTRACT FROM AUTHOR]

Co-inoculation of arbuscular mycorrhizal fungi (AMF) and bacteria can synergically and potentially increase nitrogen use efficiency (NUE) in plants, thus, reducing nitrogen (N) fertilizers use and their environmental impact. However, limited research is available on AMF-bacteria interaction, and the definition of synergisms or antagonistic effects is unexplored. In this study, we adopted a response surface methodology (RSM) to assess the optimal combination of AMF (Rhizoglomus irregulare and Funneliformis mosseae) and Bacillus megaterium (a PGPR—plant growth promoting rhizobacteria) formulations to maximize agronomical and chemical parameters linked to N utilization in maize (Zea mays L.). The fitted mathematical models, and also 3D response surface and contour plots, allowed us to determine the optimal AMF and bacterial doses, which are approximately accorded to 2.1 kg ha–1 of both formulations. These levels provided the maximum values of SPAD, aspartate, and glutamate. On the contrary, agronomic parameters were not affected, except for the nitrogen harvest index (NHI), which was slightly affected (p-value of < 0.10) and indicated a higher N accumulation in grain following inoculation with 4.1 and 0.1 kg ha–1 of AMF and B. megaterium, respectively. Nonetheless, the identification of the saddle points for asparagine and the tendency to differently allocate N when AMF or PGPR were used alone, pointed out the complexity of microorganism interaction and suggests the need for further investigations aimed at unraveling the mechanisms underlying this symbiosis.

Los Hongos Formadores de Micorrizas Arbusculares (HFMA) ayudan al intercambio y movilidad de nutrientes al asociarse con plantas, mejorando los cultivos. Por tanto, el objetivo fue evaluar HFMA en dos variedades de caña de azúcar para panela en la localidad de Suaita, Santander. Se estableció un diseño de bloques al azar, con tres repeticiones y cuatro tratamientos (T1: Acaulospora mellea, T2: Rhizoglomus irregulare, T3: Control 50% y T4: Control 100% de fertilización) en las variedades CC 93-7711 y CC 93-7510. Se analizó altura, diámetro del tallo, contenido de clorofila, absorción de nutrientes y materia seca en plantas de caña. Se presentaron diferencias significativas en la variedad CC93-7711 en la absorción de N, S, Fe, y Mn con el T2 y en contenido de clorofila a los 15 meses después de trasplante (mdt) con T1 y T2. En la variedad 93-7510 diferencias significativas a los 8 mdt en altura (T1), clorofila total (T2) y a los 15 mdt en absorción de Mn. Las dos variedades a los 15 mdt presentaron valores más altos con T1 y T2 respecto a los controles en las variables de altura, diámetro, clorofila total y materia seca. Se presentó correlación positiva entre la presencia de A. mellea con la absorción de Na, Cu, Mn, S, N y P y Rhizoglomus irregulare con Mg, Fe y Ca. Por lo anterior se puede concluir que los HFMA pueden sustituir parcialmente la fertilización de síntesis, haciéndola más efectiva, promoviendo plantas mejor nutridas con mayor producción de materia seca.

MicroRNAs (miRNAs) are non-coding small RNAs that play crucial roles in plant development and stress responses and can regulate plant interactions with beneficial soil microorganisms such as arbuscular mycorrhizal fungi (AMF). To determine if root inoculation with distinct AMF species affected miRNA expression in grapevines subjected to high temperatures, RNA-seq was conducted in leaves of grapevines inoculated with either Rhizoglomus irregulare or Funneliformis mosseae and exposed to a high-temperature treatment (HTT) of 40 °C for 4 h per day for one week. Our results showed that mycorrhizal inoculation resulted in a better plant physiological response to HTT. Amongst the 195 identified miRNAs, 83 were considered isomiRs, suggesting that isomiRs can be biologically functional in plants. The number of differentially expressed miRNAs between temperatures was higher in mycorrhizal (28) than in non-inoculated plants (17). Several miR396 family members, which target homeobox-leucine zipper proteins, were only upregulated by HTT in mycorrhizal plants. Predicted targets of HTT-induced miRNAs in mycorrhizal plants queried to STRING DB formed networks for Cox complex, and growth and stress-related transcription factors such as SQUAMOSA promoter-binding-like-proteins, homeobox-leucine zipper proteins and auxin receptors. A further cluster related to DNA polymerase was found in R. irregulare inoculated plants. The results presented herein provide new insights into miRNA regulation in mycorrhizal grapevines under heat stress and can be the basis for functional studies of plant-AMF-stress interactions.

In vitro propagation of AM fungi using transformed root cultures (TRC) is commonly used to obtain pure AM fungal propagules for use in research and industry. Early observations indicate that such an artificial environment can alter traits and function of AM fungi over time. We hypothesized that increased in vitr o cultivation may promote ruderal strategies in fungi by enhancing propagule production and reducing mutualistic quality. To examine the effect of in vitro cultivation on the trait and function of AM fungi, we inoculated plants with 11 Rhizoglomus irregulare isolates which fell along a cultivation gradient spanning 80 generations. We harvested plants at 10, 20 and 30 d post inoculation to observe differences in fungal and plant traits post infection. In vitro cultivation led to increased spore production but reduced plant shoot phosphorus. Our results indicate that in vitro propagation may indirectly select for traits that affect symbiotic quality. Image 1 • There is widescale production of in vitro AM fungal propagules for use in agriculture, research and restoration. • In vitro cultivation of AM fungi imposes selective pressure due to artificial growing conditions. • Extensive in vitro cultivation leads to increased spore production but reduced phosphorus benefits to hosts. • Thus in vitro propagation may indirectly select for traits that affect symbiotic quality. [ABSTRACT FROM AUTHOR]

BACKGROUND: Rosemary forms an arbuscular mycorrhizal (AM) symbiosis with a group of soilborne fungi belonging to the phylum Glomeromycota, which can modify the plant metabolome responsible for the antioxidant capacity and other health beneficial properties of rosemary. RESULTS: The effect of inoculating rosemary plants with an AM fungus on their growth via their polyphenolic fingerprinting was evaluated after analyzing leaf extracts from non‐inoculated and inoculated rosemary plants by ultra‐high performance liquid chromatography‐high resolution mass spectrometry (UHPLC‐HRMS). Plant growth parameters indicated that mycorrhizal inoculation significantly increased plant height and biomass. Chemical modifications in the plant polyphenolic profile distribution were found after a principal components analysis (PCA) loading plots study. Four compounds hosting strong antioxidant properties – ferulic acid, asiatic acid, carnosol, and vanillin – were related to mycorrhizal rosemary plants while caffeic and chlorogenic acids had a higher influence on non‐mycorrhizal plants. CONCLUSION: Mycorrhization was found to stimulate growth to obtain a higher biomass of plant leaves in a short time, avoiding chemical fertilization, while analytical results demonstrate that there is an alteration in the distribution of polyphenols in plants colonized by the symbiotic fungus, which can be related to an improvement in nutritional properties with future industrial significance. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract Cultivating arbuscular mycorrhizal (AM) fungi in vitro is an efficient way to produce material for industry and research. However, such artificial growing conditions may impose selective pressure on fungi grown in vitro over many generations. We hypothesized that isolates subjected to long term propagation in vitro may develop increasingly ruderal traits. We proposed a predictive framework for the effect of in vitro cultivation on asymbiotic AM fungal traits. Using photomicrography and image processing, we analyzed morphology and growth traits for 14 isolates representing an in vitro cultivation gradient from 0 to >80 generations in vitro. We investigated the range of trait variation among asymbiotic growth of arbuscular mycorrhizal (AM) fungus isolates (Rhizoglomus irregulare). Spore dormancy was strongly associated with in vitro cultivation. We observed extremely high levels of inter-isolate variation for most fungal traits, but this was not related to time in vitro. Our results indicate that intra-specific diversity may have a strong ecological role in AM fungal communities. Graphical abstract Image 1 Highlights • In vitro cultivation of arbuscular mycorrhizal fungi is an important method for industry and research. • In vitro cultivation may impose selective pressure on arbuscular mycorrhizal fungi due to artificial growing conditions. • Spore dormancy is reduced with increased in vitro cultivation. • There are extremely high levels of inter-isolate variation within Rhizoglomus irregulare not related to in vitro cultivation. [ABSTRACT FROM AUTHOR]

Highlights • We inoculated eight corn fields with an arbuscular mycorrhizal fungus. • Abundance of native mycorrhizal fungi was negatively related to soil nutrient contents. • Competitive effects to native fungal communities determined establishment success of the inoculant. • Phosphorous modulated the competitive effects between native and introduced fungi. • Crop growth response to inoculation was negatively correlated to fertilized amounts of P. Abstract A major strategy to increase the sustainability of agricultural systems consists of enhancing internal ecosystem processes that support crop production and reduce external resource inputs. However, specific approaches to achieve this goal still need to be identified. Here, we investigated whether inoculation with a high dose of a well-characterized strain of a plant symbiotic arbuscular mycorrhizal (AM) fungus into Swiss corn fields leads to successful establishment of the fungus in plant roots and can generate agronomic benefits for maize production. We used single-molecule real-time (SMRT) DNA sequencing to assess community composition of native AM fungi and identified environmental management and biological factors affecting AM fungal abundance, establishment success of the introduced fungus and effects of AMF inoculation on corn yield. While native AM fungal abundance was negatively related to soil P contents, we found significantly positive relationships between soil P contents and establishment success of the inoculated fungus. There was a significantly negative relationship between inoculum establishment and abundance of native AM fungi. Although molecular quantification using strain-specific qPCR indicated that the inoculated strain strongly increased in abundance in roots from most soils investigated, total AM fungal root colonization was only significantly increased in one soil, indicating successful competition of the inoculant for root niche space against native AM fungi. Positive effects on corn yield were only observed when inoculation increased root colonization and were negatively correlated to P fertilization levels. The results imply that phosphorus plays a major role in defining the abundance of native AM fungi and the composition of their communities and that these effects can determine establishment success of the inoculant. The results further indicate that positive effects on crop yield may only be expected when potentially achievable root colonization levels are not yet reached and AMF communities are not well developed. [ABSTRACT FROM AUTHOR]

Tomato bushy stunt virus (TBSV) and Tomato mosaic virus (ToMV) are important economic pathogens in tomato fields. Rhizoglomus irregulare is a species of arbuscular mycorrhizal (AM) fungus that provides nutrients to host plants. To understand the effect of R. irregulare on the infection by TBSV/ToMV in tomato plants, in a completely randomized design, five treatments, including uninfected control plants without AM fungi (C), uninfected control plants with AM fungi (M) TBSV/ToMV-infected plants without AM fungi (V), TBSV/ToMV-infected plants before mycorrhiza (VM) inoculation, and inoculated plants with mycorrhiza before TBSV/ToMV infection (MV), were studied. Factors including viral RNA accumulation and expression of Pathogenesis Related proteins (PR) coding genes including PR1, PR2, and PR3 in the young leaves were measured. For TBSV, a lower level of virus accumulation and a higher expression of PR genes in MV plants were observed compared to V and VM plants. In contrast, for ToMV, a higher level of virus accumulation and a lower expression of PR genes in MV plants were observed as compared to V and VM plants. These results indicated that mycorrhizal symbiosis reduces or increases the viral accumulation possibly via the regulation of PR genes in tomato plants.

Arbuscular mycorrhizal fungi (AMF) are a promising tool to improve plant nutrient use efficiency (NUE) and tolerance against abiotic stresses. Moreover, AMF can potentially increase plant productivity and reduce the negative externalities of the agricultural sector. Our study aimed to elucidate whether AMF (containing Rhizoglomus irregulare and Funneliformis mosseae) could positively affect not only tomato growth and productivity but also the nutritional and nutraceutical quality of yellow-pigmented type (‘Giagiù’) and red-pigmented type (‘Lucariello’) tomatoes (Solanum lycopersicum L.). These cherry tomatoes are landraces of the Protected Designation of Origin (PDO) ‘Pomodorino del Piennolo del Vesuvio’ (PPV), one of the most typical agricultural products of the Campania region (Southern Italy). AMF rose fruit yield by increasing the number of fruits per plant (+49% and +29% in ‘Giagiù’ and ‘Lucariello’, respectively) but not of the fruit mean mass. AMF increased lycopene (+40%), total ascorbic acid (TAA; +41%), alanine (+162%), gamma-Aminobutyric acid (GABA; +101%) and branched-chain amino acids (BCAAs; +53%) in ‘Lucariello’. In ‘Giagiù’, AMF increased calcium (+63%), zinc (+45%), ASP (+70%), GABA (+53%) and the essential amino acids arginine (+58%) and lysine (+45%), also indicating a genotype-specific response. In both landraces, AMF improved nutrient uptake and biosynthesis of important molecules involved in the control the oxidative stress and cellular pH. In addition to the beneficial effects of human health, the molecules influenced by the AMF treatment are expected to extend the shelf life of tomato fruits, thus further promoting the useful agronomic application of AMF for premium tomatoes marketed fresh or in pendulums (‘piennoli’).

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]

Arbuscular mycorrhizal fungi (AMF) are crucial components of fertile soils, able to provide several ecosystem services for crop production. Current economic, social and legislative contexts should drive the so-called "second green revolution" by better exploiting these beneficial microorganisms. Many challenges still need to be overcome to better understand the mycorrhizal symbiosis, among which (i) the biotrophic nature of AMF, constraining their production, while (ii) phosphate acts as a limiting factor for the optimal mycorrhizal inoculum application and effectiveness. Organism fitness and adaptation to the changing environment can be driven by the modulation of mitochondrial respiratory chain, strongly connected to the phosphorus processing. Nevertheless, the role of the respiratory function in mycorrhiza remains largely unexplored. We hypothesized that the two mitochondrial respiratory chain components, alternative oxidase (AOX) and cytochrome oxidase (COX), are involved in specific mycorrhizal behavior. For this, a complex approach was developed. At the pre-symbiotic phase (axenic conditions), we studied phenotypic responses of Rhizoglomus irregulare spores with two AOX and COX inhibitors [respectively, salicylhydroxamic acid (SHAM) and potassium cyanide (KCN)] and two growth regulators (abscisic acid - ABA and gibberellic acid - Ga3). At the symbiotic phase, we analyzed phenotypic and transcriptomic (genes involved in respiration, transport, and fermentation) responses in Solanum tuberosum/Rhizoglomus irregulare biosystem (glasshouse conditions): we monitored the effects driven by ABA, and explored the modulations induced by SHAM and KCN under five phosphorus concentrations. KCN and SHAM inhibited in vitro spore germination while ABA and Ga3 induced differential spore germination and hyphal patterns. ABA promoted mycorrhizal colonization, strong arbuscule intensity and positive mycorrhizal growth dependency (MGD). In ABA treated plants, R. irregulare induced down-regulation of StAOX gene isoforms and up-regulation of genes involved in plant COX pathway. In all phosphorus (P) concentrations, blocking AOX or COX induced opposite mycorrhizal patterns in planta: KCN induced higher Arum-type arbuscule density, positive MGD but lower root colonization compared to SHAM, which favored Paris-type formation and negative MGD. Following our results and current state-of-the-art knowledge, we discuss metabolic functions linked to respiration that may occur within mycorrhizal behavior. We highlight potential connections between AOX pathways and fermentation, and we propose new research and mycorrhizal application perspectives. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are promoted as biofertilizers for sustainable agriculture. Sofar, most researchers have investigated the effects of AMF on plant growth under highly controlled conditions with sterilized soil, soil substrates or soils with low available P or low inoculum potential. However, it is still poorly documented whether inoculated AMF can successfully establish in field soils with native AMF communities and enhance plant growth. We inoculated grassland microcosms planted with a grass-clover mixture (Lolium multiflorum and Trifolium pratense) with the arbuscular mycorrhizal fungus Rhizoglomus irregulare. The microcosms were filled with eight different unsterilized field soils that varied greatly in soil type and chemical characteristics and indigenousAMFcommunities.We tested whether inoculation with AMF enhanced plant biomass and R. irregulare abundance using a species specific qPCR. Inoculation increased the abundance of R. irregulare in all soils, irrespective of soil P availability, the initial abundance of R. irregulare or the abundance of native AM fungal communities. AMF inoculation had no effect on the grass but significantly enhanced clover yield in five out of eight field soils. The results demonstrate that AMF inoculation can be successful, even when soil P availability is high and native AMF communities are abundant. [ABSTRACT FROM AUTHOR]

• Mycorrhizas increased fruit yield, and quality with reduced fertilizer doses. • Deficit and optimized irrigation increased tomato yield and fruit size, but not quality. • Mycorrhiza-inoculated plants sustained yield levels with reduced fertigation. • Input efficiency should define mycorrhizal inoculant use and management. Viability of horticultural production requires high yields of high-value products, coupled with optimization of inputs. Rational fertilizer and water use are vital for the economic and environmental sustainability of vegetable production. Microbial resources are also used to increase yield, reduce inputs, and improve product quality. That includes arbuscular mycorrhizal fungi (AMF), symbionts associated with 80% of plant species, including many vegetable crops, such as tomato. To evaluate how AMF inoculation and reduced water and fertilizer affect tomato yield and quality, we carried out three independent experiments in commercial-production medium-technology (growth in soil, plastic cover, and no temperature control) greenhouses in Catalonia, Northern Spain. In the first experiment, AMF inoculation increased fruit number, total yield and improved fruit quality (soluble solids concentration or color) using lower fertilizer doses than those usually adopted on the farm. In a second assay, plants grew under three irrigation regimes: the farm usual regime, a managed-deficit regime (75% of the former), and an optimized dose using weather and plant-growth data. Deficit and optimized irrigation increased tomato yield and fruit size, but not fruit soluble solids concentration or color, and there was no effect of AMF inoculation. In the third experiment, fertigation was reduced by regulating irrigation doses according to soil moisture data. AM-inoculated plants sustained yield levels with 13% lower water and fertilizer rates. Reduced fertigation associated with AMF inoculation resulted in a 1.6% decrease in costs, which corresponds to at least six times the price of available commercial AMF inoculants. In all experiments, AMF inoculation was associated with increased water productivity, the ratio between product yield and the volume of irrigation water. Gains in input use efficiency, not only simple yield increase, should define commercial AMF inoculant use in vegetable production. We argue that researchers should estimate the financial incentive that AMF inoculation incurs so that farmers and inoculant producers have a base to test and adopt AMF inoculation technology. [ABSTRACT FROM AUTHOR]

Tomato bushy stunt virus (TBSV) and Tomato mosaic virus (ToMV) are important economic pathogens in tomato fields. Rhizoglomus irregulare is a species of arbuscular mycorrhizal (AM) fungus that provides nutrients to host plants. To understand the effect of R. irregulare on the infection by TBSV/ToMV in tomato plants, in a completely randomized design, five treatments, including uninfected control plants without AM fungi (C), uninfected control plants with AM fungi (M) TBSV/ToMV-infected plants without AM fungi (V), TBSV/ToMV-infected plants before mycorrhiza (VM) inoculation, and inoculated plants with mycorrhiza before TBSV/ToMV infection (MV), were studied. Factors including viral RNA accumulation and expression of Pathogenesis Related proteins (PR) coding genes including PR1, PR2, and PR3 in the young leaves were measured. For TBSV, a lower level of virus accumulation and a higher expression of PR genes in MV plants were observed compared to V and VM plants. In contrast, for ToMV, a higher level of virus accumulation and a lower expression of PR genes in MV plants were observed as compared to V and VM plants. These results indicated that mycorrhizal symbiosis reduces or increases the viral accumulation possibly via the regulation of PR genes in tomato plants. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are a promising tool to improve plant nutrient use efficiency (NUE) and tolerance against abiotic stresses. Moreover, AMF can potentially increase plant productivity and reduce the negative externalities of the agricultural sector. Our study aimed to elucidate whether AMF (containing Rhizoglomus irregulare and Funneliformis mosseae) could positively affect not only tomato growth and productivity but also the nutritional and nutraceutical quality of yellow-pigmented type ('Giagiù') and red-pigmented type ('Lucariello') tomatoes (Solanum lycopersicum L.). These cherry tomatoes are landraces of the Protected Designation of Origin (PDO) 'Pomodorino del Piennolo del Vesuvio' (PPV), one of the most typical agricultural products of the Campania region (Southern Italy). AMF rose fruit yield by increasing the number of fruits per plant (+49% and +29% in 'Giagiù' and 'Lucariello', respectively) but not of the fruit mean mass. AMF increased lycopene (+40%), total ascorbic acid (TAA; +41%), alanine (+162%), gamma-Aminobutyric acid (GABA; +101%) and branched-chain amino acids (BCAAs; +53%) in 'Lucariello'. In 'Giagiù', AMF increased calcium (+63%), zinc (+45%), ASP (+70%), GABA (+53%) and the essential amino acids arginine (+58%) and lysine (+45%), also indicating a genotype-specific response. In both landraces, AMF improved nutrient uptake and biosynthesis of important molecules involved in the control the oxidative stress and cellular pH. In addition to the beneficial effects of human health, the molecules influenced by the AMF treatment are expected to extend the shelf life of tomato fruits, thus further promoting the useful agronomic application of AMF for premium tomatoes marketed fresh or in pendulums ('piennoli'). [ABSTRACT FROM AUTHOR]

• Continuous cropping depresses American ginseng growth and increases pathogens. • Arbuscular mycorrhizal fungi (AMF) application improves American ginseng growth. • AMF biofertilizer increases the inoculation rate to American ginseng. • AMF enrich rhizosphere beneficial bacteria and fungi and soil available nutrients. • AMF biofertilizer suppresses rhizosphere soil-borne pathogens of American ginseng. Continuous cropping of American ginseng (Panax quinquefolius L.) is often associated with the scarcity or unavailability of soil nutrients and an imbalance of rhizosphere microbiota, resulting in low yield and poor plant quality. Inoculation with arbuscular mycorrhizal fungi (AMF) improves plant growth and production by facilitating nutrient acquisition and by modifying the abundance and diversity of rhizosphere microorganisms. In the present study, we investigated the mechanisms by which continuous cropping of American ginseng caused growth inhibition and how AMF biofertilizer application relieved these cropping obstacles. The results showed that: 1) continuous cropping of American ginseng significantly decreased the emergence rate, shoot and root dry weight, rhizosphere soil pH, the contents of ammonium, available phosphorus (P), and available potassium (K) in the rhizosphere, while increasing the root rot disease index and the soil content of nitrate; 2) continuous cropping of American ginseng decreased the diversity of bacteria, while increasing the diversity of fungi, and increased the relative abundances of Acidobacteria and Ascomycota, while decreasing the relative abundances of Actinobacteria, Firmicutes and Zygomycota; 3) in contrast, the application of AMF biofertilizer relieved the negative effects of continuous cropping American ginseng; 4) significant positive correlations were found between Pseudarthrobacter , Streptomyces and the content of ammonium, between Bacillus and the content of available K, and between Mortierella elongata and the content of available P, suggesting that the increase of rhizosphere plant-beneficial bacteria and fungi promoted the contents of available nutrients in the rhizosphere; 5) application of AMF biofertilizer significantly decreased the abundances of soil-borne pathogenic fungi Fusarium oxysporum , F. solani and the deleterious bacteria Candidatus Solibacter. In summary, our results suggest that AMF biofertilizer application improved the continuous cropping of American ginseng growth by increasing the AMF inoculation rate, by recruiting rhizosphere beneficial bacteria and fungi that promote plant-uptake of nitrogen (N) and P, and by suppressing soil-borne pathogens. Therefore, AMF biofertilizer is a probiotic agent that prevents microbial imbalances and nutrient deficiencies during continuous cropping of American ginseng. [ABSTRACT FROM AUTHOR]