Improvement of nutritional quality of greenhouse-grown lettuce by arbuscular mycorrhizal fungi is conditioned by the source of phosphorus nutrition

Microbial Biocontrol Agents and Natural Products Act as Salt Stress Mitigators in Lactuca sativa L

One of the major problems related to climate change is the increase in land area affected by higher salt concentrations and desertification. Finding economically and environmentally friendly sustainable solutions that effectively mitigate salt stress damage to plants is of great importance. In our work, some natural products and microbial biocontrol agents were evaluated for their long-term effectiveness in reducing salt stress in lettuce (Lactuca sativa L. var. romana) plants. Fourteen different treatments applied to soil pots, with and without salt stress, were analyzed using biometric (leaf and root length and width), physiological (chlorophyll and proline content), and morphological (microscopic preparations) techniques and NGS to study the microbial communities in the soil of plants subjected to different treatments. Under our long-term experimental conditions (90 days), the results showed that salt stress negatively affected plant growth. The statistical analysis showed a high variability in the responses of the different biostimulant treatments. Notably, the biocontrol agents Papiliotrema terrestris (strain PT22AV), Bacillus amyloliquefaciens (strain B07), and Rahnella aquatilis (strain 36) can act as salt stress mitigators in L. sativa. These findings suggest that both microbial biocontrol agents and certain natural products hold promise for reducing the adverse effects of salt stress on plants.

Can lettuce plants grow in saline soils supplemented with biochar?

Salt stress is presently a major environmental concern, given the huge number of soils affected by the presence of dissolved salts. Therefore, it is necessary to find solutions, preferably nature-based ones, to deal with this problem. In this study, biochar, a product made from plant biomass residues through the process of pyrolysis, was tested to alleviate salt stress on lettuce (Lactuca sativa L.) plants. Six different concentrations of NaCl were tested: 0, 50, 100, 200, 300 and 400 mM with and without the addition of 5% (w/w) biochar. Biochar ability to mitigate salinity damage was assessed by means of both biometric (fresh weight), physiological (chlorophyll content), and biochemical (i.e., electrolyte leakage, total antioxidant power, total soluble proteins, free amino acids, and mineral content) parameters. The experiment lasted four weeks. The results showed that NaCl has a negative effect from the concentration of 100-200 mM and that biochar was to some extent effective in mitigating the negative effects of salt on plant physiology; nevertheless, biochar failed to counteract Na accumulation. Similarly, biochar did not influence the content of free amino acids in lettuce leaves, but enhanced the expression of several parameters, such as total antioxidant power, fresh weight, chlorophyll content, total soluble protein, K content, although only clearly evident in some cases. Overall, the present study showed that biochar is a viable solution to counteract the damage caused by high salt concentrations on plant growth.

Do changes in Lactuca sativa metabolic performance, induced by mycorrhizal symbionts and leaf UV-B irradiation, play a role towards tolerance to a polyphagous insect pest?

The increased ultraviolet radiation (UV) due to the altered stratospheric ozone leads to multiple plant physiological and biochemical adaptations, likely affecting their interaction with other organisms, such as pests and pathogens. Arbuscular mycorrhizal fungi (AMF) and UV-B treatment can be used as eco-friendly techniques to protect crops from pests by activating plant mechanisms of resistance. In this study, we investigated plant (Lactuca sativa) response to UV-B exposure and Funneliformis mosseae (IMA1) inoculation as well as the role of a major insect pest, Spodoptera littoralis. Lettuce plants exposed to UV-B were heavier and taller than non-irradiated ones. A considerable enrichment in phenolic, flavonoid, anthocyanin, and carotenoid contents and antioxidant capacity, along with redder and more homogenous leaf color, were also observed in UV-B-treated but not in AMF-inoculated plants. Biometric and biochemical data did not differ between AMF and non-AMF plants. AMF-inoculated plants showed hyphae, arbuscules, vesicles, and spores in their roots. AMF colonization levels were not affected by UV-B irradiation. No changes in S. littoralis-feeding behavior towards treated and untreated plants were observed, suggesting the ability of this generalist herbivore to overcome the plant chemical defenses boosted by UV-B exposure. The results of this multi-factorial study shed light on how polyphagous insect pests can cope with multiple plant physiological and biochemical adaptations following biotic and abiotic preconditioning.

Leaf UV-B Irradiation and Mycorrhizal Symbionts Affect Lettuce VOC Emissions and Defence Mechanisms, but Not Aphid Feeding Preferences

Arbuscular mycorrhizal fungi (AMF) and ultraviolet-B radiation (UV-B) play important roles in plant-insect interactions by altering plant physiology and histology. We hypothesized that UV-B-induced oxidative stress was mitigated by AMF symbiosis. In this study, we conducted a multifactorial experiment to explore lettuce plant response to AMF inoculation and UV-B exposure (0.4 W m^-2; 16 h d^-1; 2 weeks), either together or individually, as well as the interaction with the polyphagous insect pest Myzus persicae (Sulzer). Lettuce plants subjected to UV-B radiation showed an increase in callose and oxidative stress indicators, as well as a decrease in stomatal density. Mycorrhizal colonization cancelled out the effect of UV-B on stomatal density, while the symbiosis was not affected by UV-B treatment. The plant volatile emission was significantly altered by UV-B treatment. Specifically, the non-terpene 1-undecene abundance (+M/+UVB: 48.0 ± 7.78%; -M/+UVB: 56.6 ± 14.90%) was increased, whereas the content of the non-terpene aldehydes decanal (+M/+UVB: 8.50 ± 3.90%; -M/+UVB: 8.0 ± 4.87%) and undecanal (+M/+UVB: 2.1 ± 0.65%; -M/+UVB: 1.20 ± 1.18%) and the sesquiterpene hydrocarbons (+M/+UVB: 18.0 ± 9.62 %; -M/+UVB: 19.2 ± 5.90%) was decreased. Mycorrhization, on the other hand, had no significant effect on the plant volatilome, regardless of UV-B treatment. Aphid population was unaffected by any of the treatments, implying a neutral plant response. Overall, this study provides new insights about the interactions among plants, UV-B, and AMF, outlining their limited impact on a polyphagous insect pest.

Engineered Nanomaterials for Improving the Nutritional Quality of Agricultural Products: A Review

To ensure food safety, the current agricultural development has put forward requirements for improving nutritional quality and reducing the harmful accumulation of agricultural chemicals. Nano-enabled sustainable agriculture and food security have been increasingly explored as a new research frontier. Nano-fertilizers show the potential to be more efficient than traditional fertilizers, reducing the amount used while ensuring plant uptake, supplying the inorganic nutrients needed by plants, and improving the process by which plants produce organic nutrients. Other agricultural uses of nanotechnology affect crop productivity and nutrient quality in addition to nano-fertilizers. This article will review the research progress of using nanomaterials to improve nutritional quality in recent years and point out the focus of future research.

The Effects of the Microbial Biostimulants Approved by EU Regulation 2019/1009 on Yield and Quality of Vegetable Crops

The use of microbial biostimulants such as plant growth-promoting rhizobacteria (PGPB) and arbuscular mycorrhizal fungi (AMF) has gained popularity in recent years as a sustainable approach to boost yield as well as the quality of produce. The beneficial effects of microbial biostimulants have been reported numerous times. However, information is missing concerning quantitative assessment of the overall impact of microbial biostimulants on the yield and quality of vegetable crops. Here we provide for the first time a comprehensive, semi-systematic review of the effects of microbial biostimulants allowed by Regulation (EU) 2019/1009, including microorganisms belonging to the AMF (phylum Glomeromycota), or to Azospirillum, Azotobacter and Rhizobium genera, on vegetable crops' quality and yield, with rigorous inclusion and exclusion criteria based on the PRISMA method. We identified, selected and critically evaluated all the relevant research studies from 2010 onward in order to provide a critical appraisal of the most recent findings related to these EU-allowed microbial biostimulants and their effects on vegetable crops' quality and yield. Moreover, we highlighted which vegetable crops received more beneficial effects from specific microbial biostimulants and the protocols employed for plant inoculation. Our study is intended to draw more attention from the scientific community to this important instrument to produce nutrient-dense vegetables in a sustainable manner. Finally, our semi-systematic review provides important microbial biostimulant application guidelines and gives extension specialists and vegetable growers insights into achieving an additional benefit from microbial biostimulant application.

Root Reinforcement Improved Performance, Productivity, and Grain Bioactive Quality of Field-Droughted Quinoa (Chenopodium quinoa)

Modern agriculture is facing multiple and complex challenges and has to produce more food and fiber to feed a growing population. Increasingly volatile weather and more extreme events such as droughts can reduce crop productivity. This implies the need for significant increases in production and the adoption of more efficient and sustainable production methods and adaptation to climate change. A new technological and environment-friendly management technique to improve the tolerance of quinoa grown to maturity is proposed using native microbial biostimulants (arbuscular mycorrhizal fungi; AMF) alone, in the consortium, or in combination with compost (Comp) as an organic matter source under two water treatments (normal irrigation and drought stress (DS)). Compared with controls, growth, grain yield, and all physiological traits under DS were significantly decreased while hydrogen peroxide, malondialdehyde, and antioxidative enzymatic functions were significantly increased. Under DS, biofertilizer application reverted physiological activities to normal levels and potentially strengthened quinoa's adaptability to water shortage as compared to untreated plants. The dual combination yielded a 97% improvement in grain dry weight. Moreover, the effectiveness of microbial and compost biostimulants as a biological tool improves grain quality and limits soil degradation under DS. Elemental concentrations, particularly macronutrients, antioxidant potential (1,1-diphenyl-2-picrylhydrazyl radical scavenging activity), and bioactive compounds (phenol and flavonoid content), were accumulated at higher levels in biofertilizer-treated quinoa grain than in untreated controls. The effects of AMF + Comp on post-harvest soil fertility traits were the most positive, with significant increases in total phosphorus (47%) and organic matter (200%) content under drought conditions. Taken together, our data demonstrate that drought stress strongly influences the physiological traits, yield, and quality of quinoa. Microbial and compost biostimulation could be an effective alternative to ensure greater recovery capability, thereby maintaining relatively high levels of grain production. Our study shows that aboveground stress responses in quinoa can be modulated by signals from the microbial/compost-treated root. Further, quinoa grains are generally of higher nutritive quality when amended and inoculated with AMF as compared to non-inoculated and compost-free plants.

Mycorrhiza-Induced Resistance against Foliar Pathogens Is Uncoupled of Nutritional Effects under Different Light Intensities

The use of microbial inoculants, particularly arbuscular mycorrhizal fungi, has great potential for sustainable crop management, which aims to reduce the use of chemical fertilizers and pesticides. However, one of the major challenges of their use in agriculture is the variability of the inoculation effects in the field, partly because of the varying environmental conditions. Light intensity and quality affect plant growth and defense, but little is known about their impacts on the benefits of mycorrhizal symbioses. We tested the effects of five different light intensities on plant nutrition and resistance to the necrotrophic foliar pathogen Botrytis cinerea in mycorrhizal and non-mycorrhizal lettuce plants. Our results evidence that mycorrhiza establishment is strongly influenced by light intensity, both regarding the extension of root colonization and the abundance of fungal vesicles within the roots. Light intensity also had significant effects on plant growth, nutrient content, and resistance to the pathogen. The effect of the mycorrhizal symbiosis on plant growth and nutrient content depended on the light intensity, and mycorrhiza efficiently reduced disease incidence and severity under all light intensities. Thus, mycorrhiza-induced resistance can be uncoupled from mycorrhizal effects on plant nutrition. Therefore, mycorrhizal symbioses can be beneficial by providing biotic stress protection even in the absence of nutritional or growth benefits.

Productivity and quality of horticultural crops through co-inoculation of arbuscular mycorrhizal fungi and plant growth promoting bacteria

Associations between plants and microorganisms exist in nature, and they can either be beneficial or detrimental to host plants. Promoting beneficial plant-microbe interaction for increased crop yield and quality is one pathway to eco-friendly and sustainable crop production. Arbuscular mycorrhizal fungi (AMF) and plant growth promoting bacteria (PGPB) are microorganisms that are beneficial to horticultural crops. Arbuscular mycorrhizal fungi establish symbioses with plant roots which help to improve nutrient uptake by the host plant and alter its physiology to withstand external abiotic factors and pathogens. Plant growth promoting bacteria promote plant growth either directly by aiding resource acquisition and controlling the levels of plant hormones or indirectly by reducing the inhibitory effects of phytopathogens. Co-inoculation of both organisms combines the benefits of each for increased crop productivity. Even though the co-inoculation of PGPB and AMF have been shown to enhance the yield and quality of crops, its benefits have fully not been exploited for horticultural crops. In this review, the response of horticultural crops to co-inoculation with PGPB and AMF with particular interest to the impact on the yield and crop quality was discussed. We explained some of the mechanisms responsible for the synergy between AMF and PGPB in plant growth promotion. Finally, suggestions on areas that need to be researched further to exploit and improve the effects of these organisms were highlighted.

Alleviation of Salt Stress in Upland Rice (Oryza sativa L. ssp. indica cv. Leum Pua) Using Arbuscular Mycorrhizal Fungi Inoculation

Arbuscular mycorrhizal fungi (AMF) symbionts not only promote the growth of host plant but also alleviate abiotic stresses. This study aimed to investigate the putative role of AMF in salt stress regulation of upland pigmented rice cv. Leum Pua (LP) comparing with Pokkali salt tolerant (positive check). In general, LP is a variety of glutinous rice that contains anthocyanin pigment in the black pericarp, due to which it possesses high antioxidant activities compared to non-pigmented rice. Pot experiment was conducted to evaluate the impact of inoculated AMF, Glomus etunicatum (GE), Glomus geosporum (GG), and Glomus mosseae (GM) strains, in the LP plantlets subjected to 0 (control) or 150 mM NaCl (salt stress) for 2 weeks in comparison with Pokkali (a salt tolerant rice cultivar), which was maintained as a positive check. Root colonization percentage under NaCl conditions ranged from 23 to 30%. Na⁺ content in the flag leaf tissues was increased to 18-35 mg g^-1 DW after exposure to 150 mM NaCl for 14 days in both inoculated and un-inoculated LP plants, whereas Na:K ratio was very low in cv. Pokkali. Interestingly, sucrose content in the flag leaf tissues of un-inoculated LP plants under salt stress was increased significantly by 50 folds over the control as an indicator of salt stress response, whereas it was unchanged in all AMF treatments. Fructose and free proline in GE inoculated plants under salt stress were accumulated over control by 5.75 and 13.59 folds, respectively, for osmotic adjustment of the cell, thereby maintaining the structure and functions of chlorophyll pigments, F_v/F_m, Φ_PSII, and stomatal function. Shoot height, flag leaf length, number of panicles, panicle length, panicle weight, and 100-grain weight in GE inoculated plants of cv. LP under salt stress were maintained similar to cv. Pokkali. Interestingly, cyanidin-3-glucoside (C3G) and peonidin-3-glucoside (P3G) in the pericarp of cv. LP were regulated by GE inoculation under salt stress conditions. In summary, AMF-inoculation in rice crop is a successful alternative approach to reduce salt toxicity, maintain the yield attributes, and regulate anthocyanins enrichment in the pericarp of grains.

Arbuscular mycorrhizal fungal inoculation and soil zinc fertilisation affect the productivity and the bioavailability of zinc and iron in durum wheat

There is a growing recognition of the role of arbuscular mycorrhizal fungi (AMF) in food security, specifically the potential for AMF to enhance the yield and mineral nutrition-including phosphorus, zinc (Zn), and iron (Fe)-of food crops. However, the bioavailability of Zn and Fe for humans in the grain of cereal crops can be overestimated by failing to consider the abundance of phytic acid (PA). This is because PA can chelate the micronutrients, making them difficult to absorb. In order to understand the effect of an AM fungus and soil Zn concentration on the productivity and nutritional quality of food parts, this study examined the growth and nutritional responses of durum wheat, with and without inoculation with Rhizophagus irregularis, at five soil Zn concentrations. Growth and nutrient responses of the plants to soil Zn amendment was stronger than responses to AMF. However, the protective effect of AMF under soil Zn toxicity conditions was observed as reduced Zn concentration in the mycorrhizal durum wheat grain at Zn50. Here, AMF inoculation increased the concentration of PA in durum wheat grain but had no effect on the concentration of Zn and Fe; this consequently reduced the predicted bioavailability of grain Zn and Fe, which could lead to a decrease in nutritional quality of the grain. This research suggests that in soil with low (available) phosphorus and Zn concentrations, AMF may reduce the food quality of durum wheat because of an increase in PA concentration, and thus, a decrease in the bioavailability of Zn and Fe.

A Reduced Phosphorus Application Rate Using a Mycorrhizal Plant as the Preceding Crop Maintains Soybean Seeds' Nutritional Quality

We tested whether introducing an arbuscular mycorrhizal fungi (AMF)-host plant with a reduced P application rate could maintain soybean seeds' nutrient quality. The dynamic variation of 14 nutrients was analyzed in source and sink organs during the seed-filling stage. The AMF-host and non-AMF-host plants, sunflower and mustard, were grown as preceding crops (PCs). Soybeans, the succeeding crops, were planted with three different phosphorus levels, namely, 0, 50, and 150 kg P2O5 ha-1. The results showed that the AMF-host PC with a reduced P application rate maintained the seed's yield and nutrients quality. During the seed-filling stage, the AMF-host PC with a reduced P application rate increased the uptake of most nutrients compared to the non-AMF-host PC, and improved the remobilization efficiency of all nutrients except Mn, Fe, and Se, compared to the optimal P application rate. These results could help improve the utilization efficiency of P fertilizers and protect soybeans' nutritional value.

Increased nutritional value in food crops

Modern agriculture and horticulture must combine two objectives that seem to be almost mutually exclusive: to satisfy the nutritional needs of an increasing human population and to minimize the negative impact on the environment. These two objectives are included in the Goal 2 of the 2030 Agenda for Sustainable Development of the United Nations: ‘End hunger, achieve food security and improved nutrition and promote sustainable agriculture'. Enhancing the nutritional levels of vegetables would improve nutrient intake without requiring an increase in consumption. In this context, the use of beneficial rhizospheric microorganisms for improving, not only growth and yield, but also the nutrient quality of crops represents a promising tool that may respond to the challenges for modern agriculture and horticulture and represents an alternative to the genetic engineering of crops. This paper summarizes the state of the art, the current difficulties associated to the use of rhizospheric microorganisms as enhancers of the nutritional quality of food crops as well as the future prospects.

This paper summarizes the state of the art, the current difficulties associated to the use of rhizospheric microorganisms as enhancers of the nutritional quality of food crops as well as the future prospects in the context of the Goal 2 of the 2030 Agenda for Sustainable Development of the United Nations: ‘End hunger, achieve food security and improved nutrition and promote sustainable agriculture'.

Influence of Rhizoglomus irregulare on nutraceutical quality and regeneration of Lycium barbarum leaves under salt stress

Whether arbuscular mycorrhizal fungi augment the nutraceutical quality of crops under salt stress is critical as a potential agronomic practice in salinized farmland. To evaluate the effect of Rhizoglomus irregulare on the nutraceutical quality of Lycium barbarum leaves under salt stress, we analyzed growth parameters and the rutin, polysaccharide, acidic polysaccharide, and amino acids contents of 2 harvests. Inoculation of R. irregulare significantly increased the regenerated bud number (partial eta squared (PES) = 0.577, P < 0.0001) and rutin concentration (PES = 0.544, P < 0.001) of L. barbarum leaves, with and without salt stress. The biomass of the 2nd harvest (PES = 0.355, P = 0.0091) and acidic polysaccharide (PES = 0.518, P = 0.001) of L. barbarum leaves were notably enhanced by R. irregulare under 200 mmol/L salt level. Rhizoglomus irregulare had insignificant effect on polysaccharide (PES = 0.092, P = 0.221) and amino acids levels (PES = 0.263, P = 0.130) in the leaves of L. barbarum. However, inoculation by R. irregulare decreased proline level (PES = 0.761, P = 0.001) in the leaves of L. barbarum when subjected to salt stress. Taken together, these results indicate that R. irregulare significantly improved the nutraceutical quality and facilitated the sustainable production of L. barbarum leaves exposed to salt stress.

Arbuscular mycorrhizal fungi and plant growth-promoting pseudomonads improve yield, quality and nutritional value of tomato: a field study

The aim of this work was to assess the effects of plant-beneficial microorganisms (two Pseudomonas strains and a mixed mycorrhizal inoculum, alone or in combination) on the quality of tomato fruits of plants grown in the field and subjected to reduced fertilization. Pseudomonas strain 19Fv1T was newly characterized during this study. The size and quality of the fruits (concentration of sugars, organic acids and vitamin C) were assessed. The microorganisms positively affected the flower and fruit production and the concentrations of sugars and vitamins in the tomato fruits. In particular, the most important effect induced by arbuscular mycorrhizal (AM) fungi was an improvement of citric acid concentration, while bacteria positively modulated sugar production and the sweetness of the tomatoes. The novelty of the present work is the application of soil microorganisms in the field, in a real industrial tomato farm. This approach provided direct information about the application of inocula, allowed the reduction of chemical inputs and positively influenced tomato quality.

Arbuscular Mycorrhizal Fungus Species Dependency Governs Better Plant Physiological Characteristics and Leaf Quality of Mulberry (Morus alba L.) Seedlings

Understanding the synergic interactions between arbuscular mycorrhizal fungi (AMF) and its host mulberry (Morus alba L.), an important perennial multipurpose plant, has theoretical and practical significance in mulberry plantation, silkworm cultivation, and relevant textile industry. In a greenhouse study, we compared functional distinctions of three genetically different AMF species (Acaulospora scrobiculata, Funneliformis mosseae, and Rhizophagus intraradices) on physiological and growth characteristics as well as leaf quality of 6-month-old mulberry seedlings. Results showed that mulberry was AMF-species dependent, and AMF colonization significantly increased shoot height and taproot length, stem base and taproot diameter, leaf and fibrous root numbers, and shoot and root biomass production. Meanwhile, leaf chlorophyll a or b and carotenoid concentrations, net photosynthetic rate, transpiration rate and stomatal conductance were generally significantly greater, while intercellular CO₂ concentration was significantly lower in AMF-inoculated seedlings than in non-AMF-inoculated counterparts. These trends were also generally true for leaf moisture, total nitrogen, all essential amino acids, histidine, proline, soluble protein, sugar, and fatty acid as they were significantly increased under mycorrhization. Among these three tested AMFs, significantly greater effects of AMF on above-mentioned mulberry physiological and growth characteristics ranked as F. mosseae > A. scrobiculata > R. intraradices, whilst on mulberry leaf quality (e.g., nutraceutical values) for better silkworm growth as F. mosseae ≈A. scrobiculata > R. intraradices. In conclusion, our results showed that greater mulberry biomass production, and nutritional quality varied with AMF species or was AMF-species dependent. Such improvements were mainly attributed to AMF-induced positive alterations of mulberry leaf photosynthetic pigments, net photosynthetic rate, transpiration rate, and N-containing compounds (methionine, threonine, histidine, and proline). As a result, application of Funneliformis mosseae or A. scrobiculata in mulberry plantation could be a promising management strategy to promote silkworm cultivation and relevant textile industry.

Inoculation with arbuscular mycorrhizal fungi improves the nutritional value of tomatoes

Arbuscular mycorrhizal (AM) fungi can affect many different micronutrients and macronutrients in plants and also influence host volatile compound synthesis. Their effect on the edible portions of plants is less clear. Two separate studies were performed to investigate whether inoculation by AM fungi (Rhizophagus irregularis, Funneliformis mosseae, or both) can affect the food quality of tomato fruits, in particular common minerals, antioxidants, carotenoids, a suite of vitamins, and flavor compounds (sugars, titratable acids, volatile compounds). It was found that AM fungal inoculation increased the nutrient quality of tomato fruits for most nutrients except vitamins. Fruit mineral concentration increased with inoculation (particularly N, P, and Cu). Similarly, inoculated plants had fruit with higher antioxidant capacity and more carotenoids. Furthermore, five volatile compounds were significantly higher in AM plants compared with non-AM controls. Taken together, these results show that AM fungi represent a promising resource for improving both sustainable food production and human nutritional needs.

Arbuscular mycorrhizal fungi affect glucosinolate and mineral element composition in leaves of Moringa oleifera

Moringa is a mycorrhizal crop cultivated in the tropics and subtropics and appreciated for its nutritive and health-promoting value. As well as improving plant mineral nutrition, arbuscular mycorrhizal fungi (AMF) can affect plant synthesis of compounds bioactive against chronic diseases in humans. Rhizophagus intraradices and Funneliformis mosseae were used in a full factorial experiment to investigate the impact of AMF on the accumulation of glucosinolates, flavonoids, phenolic acids, carotenoids, and mineral elements in moringa leaves. Levels of glucosinolates were enhanced, flavonoids and phenolic acids were not affected, levels of carotenoids (including provitamin A) were species-specifically reduced, and mineral elements were affected differently, with only Cu and Zn being increased by the AMF. This study presents novel results on AMF effects on glucosinolates in leaves and supports conclusions that the impacts of these fungi on microelement concentrations in edible plants are species dependent. The nonspecific positive effects on glucosinolates and the species-specific negative effects on carotenoids encourage research on other AMF species to achieve general benefits on bioactive compounds in moringa.

Arbuscular mycorrhizal symbiosis alleviates detrimental effects of saline reclaimed water in lettuce plants

The present study evaluated the effects of inoculation with arbuscular mycorrhizal fungi (AMF; Glomus iranicum var. tenuihypharum sp. nova) on the physiological performance and production of lettuce plants grown under greenhouse conditions and supplied with reclaimed water (RW; urban-treated wastewater with high electrical conductivity; 4.19 dS m(-1)). Four treatments, fresh water, fresh water plus AMF inoculation, RW and RW plus AMF inoculation, were applied and their effects, over time, analyzed. Root mycorrhizal colonization, plant biomass, leaf-ion content, stomatal conductance and net photosynthesis were assessed. Overall, our results highlight the significance of the AMF in alleviation of salt stress and their beneficial effects on plant growth and productivity. Inoculated plants increased the ability to acquire N, Ca, and K from both non-saline and saline media. Moreover, mycorrhization significantly reduced Na plant uptake. Under RW conditions, inoculated plants also showed a better performance of physiological parameters such as net photosynthesis, stomatal conductance and water-use efficiency than non-mycorrhizal plants. Additionally, the high concentration of nutrients already dissolved in reclaimed water suggested that adjustments in the calculation of the fertigation should be conducted by farmers. Finally, this experiment has proved that mycorrhization could be a suitable way to induce salt stress resistance in iceberg lettuce crops as plants supplied with reclaimed water satisfied minimum legal commercial size thresholds. Moreover, the maximum values of Escherichia coli in the reclaimed water were close to but never exceeded the international thresholds established (Spanish Royal Decree 1620/2007; Italian Decree, 2003) and hence lettuces were apt for sale.

Contribution of arbuscular mycorrhizal fungi to the development of maize (Zea mays L.) grown in three types of coal mine spoils

Coal mine spoils are usually unfavorable for plant growth and have different properties according to dumping years, weathering degree, and the occurrence of spontaneous combustion. The establishment of plant cover in mine spoils can be facilitated by arbuscular mycorrhizal fungi (AMF). A greenhouse pot experiment was conducted to evaluate the importance of AMF in plant adaptation to different mine spoils and the potential role of AMF for revegetation practices. We investigated the effects of Glomus aggregatum, Rhizophagus intraradices (syn. Glomus intraradices), and Funneliformis mosseae (syn. Glomus mosseae) on the growth, nutritional status, and metal uptake of maize (Zea mays L.) grown in recent discharged (S1), weathered (S2), and spontaneous combusted (S3) coal mine spoils. Symbiotic associations were successfully established between AMF and maize in three substrates. Mycorrhizal colonization effectively promoted plant growth by significantly increasing the uptake of nitrogen (N), phosphorus (P), and potassium (K), adjusting C:N:P stoichiometry and alleviating toxic effects of heavy metals. G. aggregatum, R. intraradices, and F. mosseae exhibited different mycorrhizal effects in response to mine spoil types. F. mosseae was the most effective in the development of maize in S1 and may be the most appropriate for revegetation of this substrate, while R. intraradices played the most beneficial role in S2 and S3. Our results suggest that inoculation with AMF can enhance plant adaptation to different types of coal mine spoils and play a positive role in the revegetation of coal mine spoil banks.

Effectiveness of arbuscular mycorrhizal fungi (AMF) for inducing the accumulation of major carotenoids, chlorophylls and tocopherol in green and red leaf lettuces

Previous studies demonstrated that arbuscular mycorrhizal fungi (AMF) can induce the accumulation of carotenoids, phenolics, anthocyanins and some mineral nutrients in leaves of lettuce (Lactuca sativa L.) thus enhancing its nutritional quality. Our objectives were to know which carotenoids were the most accumulated in leaves of mycorrhizal lettuces and to assess the effect of AMF on tocopherols' levels in leaves of lettuce plants. AMF always enhanced growth and, in most cases, increased the levels of all major carotenoids, chlorophylls and tocopherols in green and red leaf lettuces. Since these molecules are also important nutraceuticals, mycorrhization emerges as reliable technique to enhance the nutritional value of edible vegetables. These results are compared with other methods developed to improve nutritional quality.