Arbuscular 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.

Arbuscular Mycorrhizal Fungi Contribute to Phosphorous Uptake and Allocation Strategies of Solidago canadensis in a Phosphorous-Deficient Environment.

Arbuscular mycorrhizal fungi (AMF) can facilitate the uptake of limiting or inaccessible nutrients by plants. However, the importance of AMF for invasive plants under phosphorus (P) limitation is poorly well understood because of the presence of non-focal microorganisms, such as endophytes or rhizosphere bacteria. In this study, we investigated how an invasive clonal plant Solidago canadensis benefits from the AMF Glomus intraradices by using a completely sterile culturing system, which is composed of aseptic seedlings, a pure AMF strain, and a sterile growth environment. We found that the colonization rate, abundance, and spore production of AMF in the insoluble P treatment was more than twice as much as in the available P treatment. Plant above-ground growth was enhanced almost 50% by AMF in the insoluble P treatment. Importantly, AMF were able to facilitate P acquisition by the plant in insoluble P conditions, allowing plants to have lower investment into below-ground biomass and higher benefit/return for above-ground biomass. This study demonstrated the important contribution that AMF make to plants in phosphate-deficient environments eliminating interference from non-focal microorganisms. Our results also suggest that interaction with AMF could contribute to the invasiveness of clonal plant S. canadensis in a resource-deficient environment.

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.

Response of Vigna Unguiculata Grown Under Different Soil Moisture Regimes to the Dual Inoculation with Nitrogen-Fixing Bacteria and Arbuscular Mycorrhizal Fungi

ABSTRACTThe interaction between legumes, rhizobial and arbuscular mycorrhizal (AM) partners benefits plant nutrition and improves plant tolerance to water stress. The present research evaluated the effectiveness of symbioses between cowpea plants (Vigna unguiculata (L.) Walp.), AM fungi (Glomus intraradices) and two strains of Bradyrhizobium japonicum on the mycorrhization, acid phosphatase activity (APase), enzymes related to nitrogen fixation and assimilation, and biomass accumulation at three soil moisture levels. The results revealed that the soil moisture optimal for the formation of active symbiotrophic associations in cowpea cultivation was about 60% water-holding capacity (WHC), where both Bradyrhizobium strains and AM fungi function well with respect to mycorrhization, nitrogen and phosphorus uptake, nitrogen fixation and plant biomass production. Under conditions of reduced water supply, the symbiotic association between Br. japonicum-273 and Gl. intraradices was better for cowpea cultivation, while in elevated soil moisture association between Br. japonicum-269 and Gl. intraradices was more appropriate.

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.

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.

Direct and indirect influence of arbuscular mycorrhizal fungi on abundance and community structure of ammonia oxidizing bacteria and archaea in soil microcosms

Both arbuscular mycorrhizal (AM) fungi and ammonia oxidizers are important soil microbial groups in regulating soil N cycling. However, knowledge of their interactions, especially the direct influences of AM fungi on ammonia oxidizers is very limited to date. In the present study, a controlled microcosm experiment was established to examine the effects of AM fungi and N supply level on the abundance and community structure of ammonia oxidizing bacteria (AOB) and archaea (AOA) in the rhizosphere of alfalfa plants (Medicago sativa L.) inoculated with AM fungus Glomus intraradices. Effects were studied using combined approaches of quantitative polymerase chain reaction (qPCR) and terminal-restriction fragment length polymorphism (T-RFLP). The results showed that inoculation with AM fungi significantly increased the plant dry weights, total N and P uptake. Concomitantly, AM fungi significantly decreased the amoA gene copy numbers of AOA and AOB in the root compartment (RC) but not in the hyphal compartment (HC). Moreover, AM fungi induced some changes in AOA community structure in HC and RC, while only marginal variations in AOA composition were observed to respond to N supply level in HC. Neither RC nor HC showed significant differences in AOB composition irrespective of experimental treatments. The experimental results suggested that AM fungi could directly shape AOA composition, but more likely exerted indirect influences on AOA and AOB abundance via the plant pathway. In general, AM fungi may play an important role in mediating ammonia oxidizers, but the AOA community appeared to be more sensitive than the AOB community to AM fungi.

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.

Structure–Function Relations of Strigolactone Analogs: Activity as Plant Hormones and Plant Interactions

Strigolactones (SLs) have several functions as signaling molecules in their interactions with symbiotic arbuscular mycorrhizal (AM) fungi and the parasitic weeds Orobanche and Striga. SLs are also a new class of plant hormone regulating plant development. In all three organisms, a specific and sensitive receptor-mediated perception system is suggested. By comparing the activity of synthetic SL analogs on Arabidopsis root-hair elongation, Orobanche aegyptiaca seed germination, and hyphal branching of the AM fungus Glomus intraradices, we found that each of the tested organisms differs in its response to the various examined synthetic SL analogs. Structure-function relations of the SL analogs suggest substitutions on the A-ring as the cause of this variation. Moreover, the description of competitive antagonistic analogs suggests that the A-ring of SL can affect not only affinity to the receptor, but also the molecule's ability to activate it. The results support the conclusion that Arabidopsis, Orobanche, and AM fungi possess variations in receptor sensitivity to SL analogs, probably due to variation in SL receptors among the different species.

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.

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.

Effects of heavy metals and arbuscular mycorrhiza on the leaf proteome of a selected poplar clone: a time course analysis.

Arbuscular mycorrhizal (AM) fungi establish a mutualistic symbiosis with the roots of most plant species. While receiving photosynthates, they improve the mineral nutrition of the plant and can also increase its tolerance towards some pollutants, like heavy metals. Although the fungal symbionts exclusively colonize the plant roots, some plant responses can be systemic. Therefore, in this work a clone of Populus alba L., previously selected for its tolerance to copper and zinc, was used to investigate the effects of the symbiosis with the AM fungus Glomus intraradices on the leaf protein expression. Poplar leaf samples were collected from plants maintained in a glasshouse on polluted (copper and zinc contaminated) or unpolluted soil, after four, six and sixteen months of growth. For each harvest, about 450 proteins were reproducibly separated on 2DE maps. At the first harvest the most relevant effect on protein modulation was exerted by the AM fungi, at the second one by the metals, and at the last one by both treatments. This work demonstrates how importantly the time of sampling affects the proteome responses in perennial plants. In addition, it underlines the ability of a proteomic approach, targeted on protein identification, to depict changes in a specific pattern of protein expression, while being still far from elucidating the biological function of each protein.

Differential interaction between two Glomus intraradices strains and a phosphate solubilizing bacterium in maize rhizosphere

Abstract Arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) have a positive effect on plant productivity primarily through increasing phosphate availability. In order to study the interaction between AM fungi and PSB, we used Bacillus megaterium, a PSB isolated from the sterilized surface of AM germinated spores, and two strains of the AM fungus Glomus intraradices with different mycelial architecture. A greenhouse experiment was designed with maize as host plant with the addition of tribasic calcium phosphate. We tested the hypothesis that PSB, intimately linked with AM fungi, could interact differentially with the two AM strains. We concluded that inoculation with the PSB positively affected maize mycorrhization. Insoluble phosphate alone did not influence the AM extraradical mycelium (ERM) length and maize mycorrhization when bacteria were not inoculated. The results provide evidence that the adverse effect on infectivity for some AM strains might be caused by solubilized phosphorus release to the rhizosphere by PSB. Differences related to the mycelium architecture of each AM strain were observed: the density of PSB in rhizosphere soil was significantly higher only with the GA8 strain coinciding with the highest values of maize biomass. The density of bacteria associated with GA8 mycelium could be the result of the transfer of photosynthates through the rhizosphere; this close contact would favor the persistence of the intimate relationship between PSB and AM hyphae. In the bacteria-free treatments, soil adherence was not significantly altered. Although the highest development of ERM occurred with GA5, plants inoculated with GA8 showed the highest values for soil adherence. This may be due to the AM mycelium which modifies bacterial persistence in the rhizosphere and consequently soil adherence. Our results show that for potential applications, some characteristics of the AM strains are key in the selection of the AM fungi–PSB combinations. These include the tolerance to soluble phosphorus, the rate of root colonization, and ERM development that favors the persistence of bacteria in rhizosphere soil.

Bioprotection and alternative fertilisation of petunia using mycorrhiza in a soilless production system

Ornamental crop production is increasing worldwide and petunia is nowadays a major bedding plant with high economic impact. To meet growing demands, a high production of quality nursery plants is needed. However, production in greenhouses is confronted by two main problems: fertiliser-induced salinity and pathogen attack like by Thielaviopsis basicola which both cause high losses. Moreover, there is increasing consumer demand for crops produced by environment-friendly practices. The application of arbuscular mycorrhizal (AM) fungi can present an appropriate approach to avoid excessive use of fertilisers and pesticides. Here, we report studies of the interaction between Petunia hybrida and the AM fungus Glomus mosseae in abiotic and biotic stress situations. Root colonisation by G. mosseae, although very low, was able to compensate phosphate deficiency in the substrate and resulted in increased plant dry matter, water and phosphorus content in the shoots. However, these positive effects were attenuated at high salt concentrations (abiotic stress). In contrast, disease symptoms caused by the root pathogen T. basicola (biotic stress) were significantly reduced in G. mosseae-colonised plants. Such protective effects were not achieved with the AM fungi Glomus intraradices and Gigaspora rosea, and a negative effect of the pathogen on root colonisation by G. intraradices was observed. This shows for the first time under nursery practice conditions that G. mosseae can compensate the negative impact of lower levels of phosphate fertilisation on plant growth in a soilless production system and induce bioprotection of petunia against T. basicola. Based on the different effects observed with the three AM fungi, petunia can provide an experimental system to define the molecular mechanisms underlying mycorrhiza-induced resistance against root pathogens.

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.

Glomus intraradices Attenuates the Negative Effect of Low Pi Supply on Photosynthesis and Growth of Papaya Maradol Plants

Low inorganic phosphorus (Pi) supply limits the photosynthetic process and hence plants growth and development. Contradictory reports exist in the literature on whether mycorrhyzal association can attenuate the negative effects of low Pi supply on photosynthesis and growth. In the present paper, the effect that low Pi supply may have on photosynthesis and growth of papaya Maradol plants was evaluated in intact plants and in those inoculated with two different strains of the arbuscular mycorrhizal fungi Glomus intraradices. Plant growth was significantly reduced as the Pi supply decreased. However, inoculation with any strain of G. intraradices was able to attenuate such effect. Without Pi in the nutrient solution, the mycorrhizal plants had on average 6.1 times and 7.5 higher photosynthesis than non mycorrhizal plants. The chlorophyll fluorescence values were significantly higher in mycorrhizal than in non-mycorrhizal plants. These results could be associated to an increased ability of mycorhyzal plants to take up Pi from the substrate, as they had higher Pi content than non-mycorrhizal plants. A high correlation was found between internal Pi content and plant biomass. The lower correlation between Pi content and photosynthesis, suggests that some photosynthates could had been used to maintain the symbiosis.

Chitinase activities, scab resistance, mycorrhization rates and biomass of own-rooted and grafted transgenic apple.

This study investigated the impact of constitutively expressed Trichoderma atroviride genes encoding exochitinase nag70 or endochitinase ech42 in transgenic lines of the apple cultivar Pinova on the symbiosis with arbuscular mycorrhizal fungi (AMF). We compared the exo- and endochitinase activities of leaves and roots from non-transgenic Pinova and the transgenic lines T386 and T389. Local and systemic effects were examined using own-rooted trees and trees grafted onto rootstock M9. Scab susceptibility was also assessed in own-rooted and grafted trees. AMF root colonization was assessed microscopically in the roots of apple trees cultivated in pots with artificial substrate and inoculated with the AMF Glomus intraradices and Glomus mosseae. Own-rooted transgenic lines had significantly higher chitinase activities in their leaves and roots compared to non-transgenic Pinova. Both of the own-rooted transgenic lines showed significantly fewer symptoms of scab infection as well as significantly lower root colonization by AMF. Biomass production was significantly reduced in both own-rooted transgenic lines. Rootstock M9 influenced chitinase activities in the leaves of grafted scions. When grafted onto M9, the leaf chitinase activities of non-transgenic Pinova (M9/Pinova) and transgenic lines (M9/T386 and M9/T389) were not as different as when grown on their own roots. M9/T386 and M9/T389 were only temporarily less infected by scab than M9/Pinova. M9/T386 and M9/T389 did not differ significantly from M9/Pinova in their root chitinase activities, AMF root colonization and biomass.