Mycorrhizal Fungus Glomus Intraradices Research Articles

Solarized IPM Module for Biocontrol of Root-knot Nematode on Tomato at Nursery Level in District G.B Nagar, Uttar Pradesh

Background: The role of soil solarization in suppression of soil borne pathogens and weeds has been established by several researchers around the globe It involves capturing solar radiations when the soil receives the maximum sunlight in May-June using a polythene mulch. Its effectiveness depends on ambient temperature, duration of the treatments and soil moisture. This not only acts as a soil disinfectant but also as soil decontamination. It includes various changes in the soil like physical, chemical and biological properties. Methods: The field to lab and vice-versal based investigations were carried during 2021-2022 at Amity Centre for Biocontrol and Plant Disease Management, Amity University, Uttar Pradesh, Noida and identified tomato nurseries of district G B Nagar where heavy infestation (10-12 J2/cc soil) of root knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood was recorded. The treatments comprised of sustainable components viz. deoiled seed cake of neem, a Arbuscular Mycorrhizal fungus Glomus intraradices and indigenous fungal strain of Trichoderma harzianum, (Th7) alone and together applied for evolving IPM module at solarized and unsolarized sets. Under microplot trials, the entire solarized treatments were carried out measuring 3 × 1 sq. meter each in which one set of all the treatments including control covered with clear transparent polythene sheet (400 ì gauge) for solarization. The treatments were replicated thrice in randomized block design. Result: The observations of solarized and unsolarized treatments clearly revealed that the soil solarization in treatments where the sun radiant energy was trapped by 400 µ transparent polysheets significantly reduced the root knot nematode Meloidogyne incognita population both in root and soil in comparison to unsolarized treatments where no solar energy trapping was done. The combined application of locally isolated Trichoderma harzianum (Th7) and VA mycorrhiza, Glomus intraredices enhanced germination and plant growth in nurseries. In the present investigation, the solarized IPM module- 4 comprising of other sustainable components viz. neem oil-seed cake, T. harzianum (Th-7) and Arbuscular Mycorrhizal (AM) fungus G. intraredices is proved to be an ideal one in root-knot nematode pest management in tomato nurseries.

Application of biological products at cultivation of garden pea Pisum sativum l.

The possibilities of using the biological products “Trichodermine” (Trichoderma viride Pers ex Fr.), “Gliocladine” (Gliocladium virens Miller et al.) and the mycorrhizal activator “Rhizo VAM Basic” (Glomus intraradices Schenck&Smith) for control of fungal diseases in garden pea and and their impact on the biometric indicators of young plants were studied. Biological preparations based on antagonistic fungi Trichoderma viride and Gliocladium virens improve the phytosanitary condition of the plants, the mycorrhizal fungus Glomus intraradices stimulates the formation of the root system and tuber formation, but has a weak fungicidal effect against Fusarium wilt in this culture. The experiment was performed on an artificial infectious background by Fusarium oxysporum Schlecht. f. sp. pisi (Hal.) Raillo, isolated from diseased plants. The effect of application of the biological products“Trichodermine” and “Gliocladine” is 34-68%, from “Rhizo VAM Basic” - 8% compared to the infected control. The combined application of biological preparations with fungicidal and mycorrhizal action significantly protects the crop from infection with the causative agent of Fusarium wilt of garden pea.

Biostimulants as a Tool for Improving Environmental Sustainability of Greenhouse Vegetable Crops

Plant biostimulants have gained great interest from the agrochemical industry and farmers because of their ability to enhance nutrient use efficiency and increase abiotic stress tolerance in crop production. However, despite the considerable potential of biostimulants for the sustainable development of the agricultural sector, the environmental evaluation of the application of biostimulants is still missing. Hence, this is the first study that focuses on the environmental assessment of the biostimulant action of arbuscular mycorrhizal fungus Glomus intraradices and vegetal-derived protein hydrolysate on two greenhouse vegetable crops, spinach and zucchini squash, under different fertilization regimes. The life cycle assessment from a cradle to gate perspective, which covers all processes related to crop cultivation up to harvest, was carried out to calculate the carbon footprint of the production chain for these two crops. The results of the comparative analysis revealed that the CO2 equivalent emissions of both crops were reduced due to the biostimulant applications. In particular, the effect of the mycorrhization on the reduction of carbon emissions compared to the un-mycorrhized control was higher in zucchini plants under organic fertilization (12%) than under mineral fertilization (7%). In addition, organic fertilization increased the total carbon footprint of zucchini (52%) compared with mineral fertilization. The results also showed that an increase of nitrogen fertilization from 15 to 45 kg N ha−1 in spinach production enhanced the total CO2 emissions per ton of harvested leaves in comparison with treatments that involved the foliar applications of protein hydrolysate together with a lower nitrogen input; this increase was 4% compared to the unfertilized treatment with application of biostimulant. This study can support decision-making in terms of agronomic technique choices in line with sustainable development of vegetable crop production.

Can Salvia splendens ‘Red Vista’ be used in association with the mycorrhizal fungus Glomus intraradices for the assisted phytoextraction of lead from the soil in Lima, Peru?

In Peru, gasoline containing lead as a main component was used in vehicles up until 2006, when the Government banned its sale. However, since this was preceded by a century of constant use, there is a high chance that most urban soils are polluted with this heavy metal. Hyperaccumulator plants that take up heavy metals from the soil and store them in their tissues without showing any symptoms of toxicity may be the solution to this problem, as the use of these plants for phytoremediation does not require large amounts of money, can be carried out in situ, and is environmentally friendly, making it one of the best options for urban areas. However, unfortunately, there are only a few known species of hyperaccumulator plants that can be grown in urban environments. Therefore, we conducted a bioassay at the Soil Fertility Laboratory of the Agronomy Faculty at the National Agrarian University La Molina, Peru, over a period of 4 months to determine the hyperaccumulation capacity of Salvia splendens ‘Red Vista’ and to examine whether the mycorrhizal fungus Glomus intraradices can enhance the extraction of lead from the soil. After harvest, the plants were divided into three parts (roots, leaves, and inflorescences) to determine the concentrations of lead in the various tissues. We found that S. splendens ‘Red Vista’ did not accumulate high amounts of lead in its tissues even when it was associated with G. intraradices and consequently should not be considered for use in phytoextraction.

Relationship between chlorosis, photosynthesis and the nutrient content of plane trees in the presence of chemical and organic fertilizers

Chlorosis disorder is a major problem affecting the growth and physiological processes of many trees including plane trees (Platanus orientalis L.). This experiment was conducted to study the relationship between leaf chlorosis disorder and the nutritional status and some important physiological characteristics of plane trees. The experiment was arranged in a randomized complete block design with six replications and four treatments including control, manure (M), manure + fertilizer (20-5-10) (MF), and manure + fertilizer + mycorrhizal fungi (MFA) ( Glomus intraradices + G. mosseae) . The results showed that although all treatments significantly improved the nutrients content, soluble carbohydrates content, photosynthesis rate and chlorophyll content in the leaves, they mostly reached their peak in the mycorrhizal inoculated plants. Nitrogen (N), phosphorus (P) and zinc (Zn) were increased in the AMF amended trees compared to the control plants. The photosynthesis rate was enhanced by all the mixtures at least by 60% compared to the control. The most Chlorosis (17.5%) to the leaves recorded on the control plants, while leaf damage dropped to less than 2.9% at mycorrhizal treatment leading to the improved nutritional balance in the plane trees. The results proved the effectiveness of including mycorrhizal inoculation to the common fertilization practices to prevent leaf chlorosis in the plane trees.

Effect of arbuscular mycorrhizal fungi and water stress on ultrastructural change of glandular hairs and essential oil compositions in Ocimum gratissimum

BackgroundThe objective of this work is to study the influence of arbuscal mycorrhizal fungi (Glomus intraradices) and water stress on the ultrastructural change of basil glandular hair and also on the essential oil synthesis, especially on the isomerization of the two main compounds methyl chavicol and trans-anethole.ResultsThe results of this study show that mycorrhization increases the yield of essential oils, with a maximum recorded in mycorrhizal stressed plants (0.33%) and a minimum among non-mycorrhizal unstressed plants (0.22%). Oxygenated monoterpenes represent the main family of essential oils. Furthermore, the chemical composition of these essential oils changed under the condition in which the plant is. However, the main compound methyl chavicol was found to be at maximum concentration (93%) in mycorrhizal stressed plants and minimum in non-mycorrhizal stressed plants (84%). Contrariwise, its isomer trans-anethole reached the maximum (8%) among non-mycorrhizal non-stressed plants and minimum (2%) in non-mycorrhizal stressed plants.ConclusionOcimum gratissimum L. leaves showed the presence of two types of peltate glands: the first one with 4 secreting cells and the second with 8 secreting cells. The diameter of these glands changed with the hydric state of plants; in the absence of mycorrhization, stress causes a decrease in the extracellular cavity diameter of glandular trichomes and their deflation which would cause a concentration of essential oil in the glands.Graphical abstractEffect of arbuscular mycorrhizal fungi and water stress on essential oil yield and compositions by the change in some endogenous plant growth regulators and glandular hairs morphology and density in Ocimum gratissimum

The Use of Coal Gangue as a Cultivation Bed Conditioner in Forage Maize Inoculated with Arbuscular Mycorrhizal Fungi

ABSTRACTA greenhouse pot experiment was conducted to investigate the effect of application of coal gangue (CG) at different rates (0, 5, 10, 20, and 50%) and inoculation with two arbuscular mycorrhizal (AM) fungi Glomus intraradices and Glomus mosseae, as mediating plant adaptation to soil amended with CG, on the nutrient content of forage maize. The results showed CG amendment at all levels and both AM fungi significantly improved the nutrient content of the plant as compared to control. In general, the highest shoot dry weight and nutrient phosphorus, iron, and zinc (P, Fe, and Zn) were obtained with 10% CG and G. intraradice treatments, which were 49.68, 30.49, 16.72, and 75.71% higher than those of the control plants, respectively. Therefore, 10% dose of CG may be considered as a suitable dose for amendment in the corn cultivation bed in terms of providing nutrient contents for this plant as well as AM fungi root colonization.

Alleviatory activities in mycorrhizal tobacco plants subjected to increasing chloride in irrigation water

The effects of presence and absence of arbuscular mycorrhizal (AM+ and AM-) fungus (AMF) Glomus intraradices on agronomic and chemical characteristics of field-grown tobacco (Nicotiana tabacum L.) Virginia type (cv. K-326) plants exposed to varying concentrations of chloride 10, 40, 70 and 100 mg Cl L–1 (C1-C4) were studied over two growing seasons (2012-2013). Mycorrhizal plants had significantly higher uptake of nutrients in shoots and number of leaves regardless of intensities of chloride stress. The cured leaves yields of AM+ plants under C2-C4 chloride stressed conditions were higher than AM- plants. Leaf chloride content increased in line with the increase of chloride level, while AMF colonised plants maintained low Cl content. AM+ plants produced tobacco leaves that contained significantly higher quantities of nicotine than AM- plants. AM inoculation ameliorated the chloride stress to some extent. Antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase as well as non-enzymatic antioxidants (ascorbic acid and glutathione) also exhibited great variation with chloride treatment. Chloride stress caused great alterations in the endogenous levels of growth hormones with abscisic acid showing increment. AMF inoculated plants maintained higher levels of growth hormones and also allayed the negative impact of chloride. The level of 40 mg L–1 in combination with arbuscular mycorrhizal can be considered as the acceptable threshold to avoid adverse effects on Virginia tobacco.

Bioremediation Effect of Contaminated Soils with Copper and Lead on Sweet Basil Plants

The effects of phosphorus amendments and arbuscular mycorrhizal (AM) fungi Glomus intraradices and pseudomonas putida on the sweet basil (Ocimum basilicum L.) yield, chemical composition and percent of volatile oil, and metal accumulation in plants and its availability in soil were investigated in field experiment at two seasons 2012 and 2013 under contaminated soil with Pb and Cu. The plant height, herb fresh weight, content of essential oil and shoot and root dry weights of sweet basil were increased by the application of mineral phosphorus as compared to control. Inoculation with AM fungi and bacteria reduced the metal concentration in shoot, recording a lowest value of (33.24, 18.60 mg/kg) compared to the control (46.49, 23.46 mg/kg) for Pb and Cu, respectively. Availability of Pb and Cu in soil were decreased after cultivation in all treatments compared to control. However, metal root concentration increased with the inoculation, with highest values of (30.15, 39.25 mg/kg)compared to control (22.01, 33.57mg/kg) for Pb and Cu, respectively. The content of linalool and methyl chavicol in basil oil was significantly increased in all treatments compared to control, but the interaction was not. We can thus conclude that the AM-sweet basil symbiosis and bacterial inoculation could be employed as an approach to bioremediate polluted soils and enhance the yield and maintain the quality of volatile oil of sweet basil plants.

Optimizing phosphorus use in sustainable maize cropping via mycorrhizal inoculation

ABSTRACTMore details have yet to be indicated on the interactions between arbuscular mycorrhizal (AM) fungi and phosphorus (P) chemical fertilization under field conditions. Accordingly, the objectives were to: (1) evaluate the combined effects of mycorrhizal fungi and chemical P fertilization on maize yield, yield components, and nutrient uptake and (2) indicate the optimum rate of P chemical fertilization (P1, P2, P3) with the use of mycorrhizal fungi (Glomus intraradices and G. mosseae). A factorial experiment using randomized complete blocks with three replicates, conducted at the Research Station of the Faculty of Agriculture, Islamic Azad University, Tabriz branch, Iran. Results indicated the significant effect of P, AM fungi, and their interaction on most of the measured traits. Grain yield (7909.3 kg/ha), maize nutrient content of P (0.39%), zinc (Zn) (42.1 mg/kg), iron (Fe) (68.3 mg/kg), and the colonization rate (47.5%) were all the highest by the interaction of G intraradices × P2.

Mycorrhizal Inoculation and High Arsenic Concentrations in the Soil Increase the Survival of Soybean Plants Subjected to Strong Water Stress

Soybean (Glycine max L.) cropping is increasing in marginal environments, including water-limited lands, some of which are loaded with arsenic (As). Plants inoculated with mycorrhiza increased their tolerance to water stress. We studied the effect of a sudden and severe water stress on soybean inoculated with the mycorrhizal fungus Glomus intraradices in soils with increasing concentrations of As. Soybean plants were grown in greenhouse with adequate water supply for 60 days. Irrigation was stopped completely and soil abruptly reached the permanent wilting point. Most inoculated plants survived under such limiting water stress, but noninoculated plants were clearly affected. Arsenic showed a negative effect on plant growth but improved plant survival under this severe water stress. It seems that the negative effects of As on plant water equilibrium explain why plants affected by As survived extreme water stress events.

Use of the arbuscular mycorrhizal fungus Glomus intraradices as biological control agent of the nematode Nacobbus aberrans parasitizing tomato

ABSTRACT The plant-parasitic nematode Nacobbus aberrans is an endoparasite that induces gall formation in the roots and causes severe losses to diverse crops. Some populations of this nematode show preference for certain hosts, revealing the existence of “races/groups” with diff erent behaviour and making nematode management difficult. A possible biological control alternative to reduce the damage caused by this species may be the use of arbuscular mycorrhizal fungi (AMF). In the present work, the effect of Glomus intraradices on tomato plants inoculated with the nematode at transplanting and three weeks later was tested. At 60 days, the following parameters were estimated: percentage of AMF colonization, root and aerial dry weight, number of galls and egg masses, and reproduction factor (RF=final population/initial population) of N. aberrans . AMF colonization was higher in the presence of the nematode. The use of AMF favoured tomato biomass and reduced the number of galls and RF on the plants inoculated with the nematode at transplanting. Key words: arbuscular mycorrhiza, false root-knot nematode, microbiological control, plant protection

Establishing monoxenic culture of arbuscular mycorrhizal fungus Glomus intraradices through root organ culture

Arbuscular mycorrhizal fungi are soil fungi distributed worldwide, forming symbiosis with most of the vascular plants for their growth and survival, which is used for sustainable agriculture and ecosystem management. This study investigated the establishment of monoxenic cultures of Glomus intraradices in association with transformed carrot hairy root. The G.intraradices spores were isolated from sugarcane rhizosphere by wet sieving and decanting technique and propagated in open pot culture. Transformation in to carrot hairy root was done using Agrobacterium rhizogenes. Surface sterilization of G.intraradices spores co-cultured with transformed carrot hairy root in Modified Strulla and Romand (MSR) medium was found the host root growth as well as for germination AM spores. After three months of incubation in dark condition, significant production of extensive hyphal growth on MSR medium and an average of 8500-9000 spores per petri dish was observed. The in vitro inoculum exhibited higher potential of root colonization due to numerous intraradices mycelium with extensive spore load. The produced monoxenic inoculum can be used in place of traditional system where it has a advantage of producing contaminant free propagulas. Thus the monoxenic culture system, a powerful tool, of AM sporulation, can be used for the mass production of monoxenic inoculum of AM fungi besides studying its biology.

The cis‐acting CTTC–P1BS module is indicative for gene function of LjVTI12, a Qb‐SNARE protein gene that is required for arbuscule formation in Lotus japonicus

The majority of land plants live in symbiosis with arbuscular mycorrhizal fungi from the phylum Glomeromycota. This symbiosis improves acquisition of phosphorus (P) by the host plant in exchange for carbohydrates, especially under low-P availability. The symbiosome, constituted by root cortex cells accommodating arbuscular mycorrhizal fungal hyphae, is the site at which bi-directional exchange of nutrients and metabolites takes place. Uptake of orthophosphate (Pi) in the symbiosome is facilitated by mycorrhiza-specific plant Pi transporters. Modifications of the potato Pi transporter 3 (StPT3) promoter were analysed in transgenic mycorrhizal roots, and it was found that the CTTC cis-regulatory element is necessary and sufficient for a transcriptional response to fungal colonization under low-Pi conditions. Phylogenetic footprinting also revealed binary combination of the CTTC element with the Pi starvation response-associated PHR1-binding site (P1BS) in the promoters of several mycorrhiza-specific Pi transporter genes. Scanning of the Lotus japonicus genome for gene promoters containing both cis-regulatory elements revealed a strong over-representation of genes involved in transport processes. One of these, LjVTI12, encoding a member of the SNARE family of proteins involved in membrane transport, exhibited enhanced transcript levels in Lotus roots colonized with the arbuscular mycorrhizal fungus Glomus intraradices. Down-regulation of LjVTI12 by RNA interference resulted in a mycorrhiza-specific phenotype characterized by distorted arbuscule morphology. The results highlight cooperative cis-regulation which integrates mycorrhiza and Pi starvation signaling with vesicle trafficking in symbiosome development.

Rhizobial and mycorrhizal symbioses in Lotus japonicus require lectin nucleotide phosphohydrolase, which acts upstream of calcium signaling.

Nodulation in legumes requires the recognition of rhizobially made Nod factors. Genetic studies have revealed that the perception of Nod factors involves LysM domain receptor-like kinases, while biochemical approaches have identified LECTIN NUCLEOTIDE PHOSPHOHYDROLASE (LNP) as a Nod factor-binding protein. Here, we show that antisense inhibition of LNP blocks nodulation in Lotus japonicus. This absence of nodulation was due to a defect in Nod factor signaling based on the observations that the early nodulation gene NODULE INCEPTION was not induced and that both Nod factor-induced perinuclear calcium spiking and calcium influx at the root hair tip were blocked. However, Nod factor did induce root hair deformation in the LNP antisense lines. LNP is also required for infection by the mycorrhizal fungus Glomus intraradices, suggesting that LNP plays a role in the common signaling pathway shared by the rhizobial and mycorrhizal symbioses. Taken together, these observations indicate that LNP acts at a novel position in the early stages of symbiosis signaling. We propose that LNP functions at the earliest stage of the common nodulation and mycorrhization symbiosis signaling pathway downstream of the Nod factor receptors; it may act either by influencing signaling via changes in external nucleotides or in conjunction with the LysM receptor-like kinases for recognition of Nod factor.

The Medicago truncatula Sucrose Transporter Family: Characterization and Implication of Key Members in Carbon Partitioning towards Arbuscular Mycorrhizal Fungi

We identified de novo sucrose transporter (SUT) genes involved in long-distance transport of sucrose from photosynthetic source leaves towards sink organs in the model leguminous species Medicago truncatula. The identification and functional analysis of sugar transporters provide key information on mechanisms that underlie carbon partitioning in plant-microorganism interactions. In that way, full-length sequences of the M. truncatula SUT (MtSUT) family were retrieved and biochemical characterization of MtSUT members was performed by heterologous expression in yeast. The MtSUT family now comprises six genes which distribute among Dicotyledonous clades. MtSUT1-1 and MtSUT4-1 are key members in regard to their expression profiles in source leaves and sink roots and were characterized as functional H(+)/sucrose transporters. Physiological and molecular responses to phosphorus supply and inoculation by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices was studied by gene expression and sugar quantification analyses. Sucrose represents the main sugar transport form in M. truncatula and the expression profiles of MtSUT1-1, MtSUT2, and MtSUT4-1 highlight a fine-tuning regulation for beneficial sugar fluxes towards the fungal symbiont. Taken together, these results suggest distinct functions for proteins from the SUT1, SUT2, and SUT4 clades in plant and in biotrophic interactions.

Efficiency of Sandy Everlasting [Helichrysum arenarium (L.) Moench] cultivation from in vitro seedlings and achenes

Sandy Everlasting [Helichrysum arenarium (L.) Moench] is a perennial of the Asteraceae family whose inflorescences (Inflorescentia Helichrysi=Flos Stoechados citrini) are valuable herbal material. The influence of different soil types (sandy vs. clayey soil) on the growth and further development of in vitro seedlings was studied in field experiments. Separate experiments showed the influence of sowing time (late autumn vs. early spring) and the inoculation with a mycorrhizal fungus Glomus intraradices on the development of the plants developing from achenes. For comparison purposes the results of biometric measurements obtained in the second year of flowering were selected, although it might fall on different calendar years. This was due to the fact that the most intensive growth and the most abundant flowering occurred in the third year of cultivation, regardless of the cultivation method and weather conditions. These studies demonstrated that both cultivation methods were feasible, as each of them yielded a particular amount of valuable, raw herbal material. Each method generates some costs and has its own advantages and disadvantages. The in vitro technique seems to be more profitable as it allows the acquisition of a potentially unlimited number of shapely plants that flower at the same time. This method is also less harmful to the natural environment.

Vesicular-arbuscular (VA) mycorrhizae improve salinity tolerance in pre-inoculation subterranean clover (Trifolium subterraneum) seedlings

Effects of the mycorrhizal fungus Glomus intraradices on establishment of subterranean clover (Trifolium subterraneum L.) seedlings in saline conditions were studied in a glasshouse experiment. Growth and nutrient uptake were determined 10, 20 and 30 days after transplanting of mycorrhizal and nonmycorrhizal matched seedlings into soils with five different levels of salinity. Mycorrhizal plants had greater shoot and root dry weight than nonmycorrhizal plants. The enhancement in seedling dry weight due to mycorrhizal fungi was greater under high salinity levels. The detrimental effects of salinity stress on plant growth were appeared immediately after application low salinity stress to nonmycorrhizal plants (3.5 dS/m), but it was only observed in mycorrhizal plants at 7.5 dS/m and above. Mycorrhizal fungi increased P concentrations in shoots and roots compared with nonmycorrhizal plants particularly at 12 dS/m. Root K/Na ratio was also increased in mycorrhizal plants, possibly contributing to salinity tolerance. Calculation of mycorrhizal responses in terms of plant dry weight, P and K contents showed that the beneficial effects of mycorrhizal fungi on seedling salinity tolerance are due to different mechanisms at different stage of growth: increased P uptake during early growth and increased K uptake at the later stages. Results are discussed in the context of application of mycorrhizal inoculation to revegetation of salt affected lands.

The symbiotic recapture of nitrogen from dead mycorrhizal and non-mycorrhizal roots of tomato plants

AbstractAimsThe aim was to quantify the nitrogen (N) transferred via the extra-radical mycelium of the arbuscular mycorrhizal fungusGlomus intraradicesfrom both a dead host and a dead non-host donor root to a receiver tomato plant. The effect of a physical disruption of the soil containing donor plant roots and fungal mycelium on the effectiveness of N transfer was also examined.MethodsThe root systems of the donor (wild type tomato plants or the mycorrhiza-defectivermcmutant tomato) and the receiver plants were separated by a 30 μm mesh, penetrable by hyphae but not by the roots. Both donor genotypes produced a similar quantity of biomass and had a similar nutrient status. Two weeks after the supply of15 N to a split-root part of donor plants, the shoots were removed to kill the plants. The quantity of N transferred from the dead roots into the receiver plants was measured after a further 2 weeks.ResultsUp to 10.6 % of donor-root15N was recovered in the receiver plants when inoculated with the arbuscular mycorrhizal fungus (AMF). The quantity of15N derived from the mycorrhizal wild type roots clearly exceeded that from the only weakly surface-colonisedrmcroots. Hyphal length in the donorrmcroot compartments was only about half that in the wild type compartments. The disruption of the soil led to a significantly increased AMF-mediated transfer of N to the receiver plants.ConclusionsThe transfer of N from dead roots can be enhanced by AMF, especially when the donor roots have been formerly colonised by AMF. The transfer can be further increased with higher hyphae length densities, and the present data also suggest that a direct link between receiver mycelium and internal fungal structures in dead roots may in addition facilitate N transfer. The mechanical disruption of soil containing dead roots may increase the subsequent availability of nutrients, thus promoting mycorrhizal N uptake. When associated with a living plant, the external mycelium ofG. intraradicesis readily able to re-establish itself in the soil following disruption and functions as a transfer vessel.

GiFRD encodes a protein involved in anaerobic growth in the arbuscular mycorrhizal fungus Glomus intraradices

Fumarate reductase is a protein involved in the maintenance of redox balance during oxygen deficiency. This enzyme irreversibly catalyzes the reduction of fumarate to succinate and requires flavin cofactors as electron donors. Two examples are the soluble mitochondrial and the cytosolic fumarate reductases of Saccharomyces cerevisiae encoded by the OSM1 and FRDS1 genes, respectively.This work reports the identification and characterization of the gene encoding cytosolic fumarate reductase enzyme in the arbuscular mycorrhizal fungus, Glomus intraradices and the establishment of its physiological role. Using a yeast expression system, we demonstrate that G. intraradices GiFRD encodes a protein that has fumarate reductase activity which can functionally substitute for the S. cerevisiae fumarate reductases. Additionally, we showed that GiFRD transformants are not affected by presence of salt in medium, indicating that the presence of this gene has no effect on yeast behavior under osmotic stress. The fact that GiFRD expression and enzymatic activity was present only in asymbiotic stage confirmed existence of at least one anaerobic metabolic pathway in this phase of fungus life cycle. This suggests that the AMF behave as facultative anaerobes in the asymbiotic stage.