Arbuscular Mycorrhiza Infection Research Articles

AM-Induced Alteration in the Expression of Genes, Encoding Phosphorus Transporters and Enzymes of Carbohydrate Metabolism in Medicago lupulina.

Plant–microbe interactions, including those of arbuscular mycorrhiza (AM), have been investigated for a wide spectrum of model plants. The present study focuses on an analysis of gene expression that encodes phosphate and sugar transporters and carbohydrate metabolic enzymes in a new model plant, the highly mycotrophic Medicago lupulina MLS-1 line under conditions of phosphorus deficiency and inoculation with Rhizophagus irregularis. Expression profiles were detected by RT-PCR at six plant stages of development (second leaf, third leaf, shooting, axillary shoot branching initiation, axillary shoot branching, flowering initiation). In comparison to control (without AM), the variant with AM inoculation exhibited a significant elevation of transcription levels of carbohydrate metabolic enzymes (MlSUS, MlHXK1) and sucrose transporters (MlSUC4) in M. lupulina leaves at the shooting stage. We suggest that this leads to a significant increase in the frequency of AM infection, an abundance of mycelium in roots and an increase in AM efficiency (which is calculated by the fresh weight of aerial parts and roots at the axillary shoot branching initiation stage). In roots, the specificity of MlPT4 and MlATP1 gene expressions were revealed for effective AM symbiosis. The level of MlPT4 transcripts in AM roots increased more than tenfold in comparison to that of non-specific MlPT1 and MlPT2. For the first time, MlPT1 expression was shown to increase sharply against MlPT2 in M. lupulina roots without AM at the shooting initiation stage. A significant increase in MlRUB expression was revealed at late stages in the host plant’s development, during axillary shoot branching and flowering initiation. The opposite changes characterized MlHXK1 expression. Alteration in MlHXK1 gene transcription was the same, but was more pronounced in roots. The obtained results indicate the importance of genes that encode phosphate transporters and the enzymes of carbohydrate metabolism for effective AM development at the shooting stage in the host plant.

Expression of four phosphate transporter genes from Finger millet (Eleusine coracana L.) in response to mycorrhizal colonization and Pi stress

Phosphorus (P) is a vital nutrient for plant growth and development, and is absorbed in cells with the help of membrane-spanning inorganic phosphate transporter (Pht) protein. Symbiosis with arbuscular mycorrhiza (AM) also helps in transporting P from the soil to plant and Pht proteins play an important role in it. To understand this phenomenon in Finger Mille plant, we have cloned four Pht genes from Finger millet, which shares the homology with Pht1 protein family of cereals. Expression pattern analysis during the AM infection indicated that EcPT4 gene was AM specific, and its expression was higher in roots where AM colonization percentage was high. The expression level of EcPT1-4 gene under the phosphorous (Pi) stress in seedlings was found to be consistent with its role in acquisition of phosphorus. Homology study of the EcPt proteins with Pht proteins of cereals shows close relationship. The findings of the study indicate that Pht1 family genes from finger millet can serve to be an important resource for the better understanding of phosphorus use efficiency.

Growth and Nutrient Uptake Responses of Kinnow to Vesicular Arbuscular Mycorrhizae

In a field experiment, three-year-old Kinnow trees budded on Jatti Katti (C. jambhiri) rootstock were inoculated by three different arbuscular mycorrhiza (AM), Glomus manihotis (T1), Glomus mosseae (T2), and Gigaspora gigantia (T3), separately or in combination (T4). Microscopic assessment of AM colonization on Kinnow roots showed a relatively lower level of infection by different species when inoculated separately than when inoculaed together. Application of AM improved growth parameters like plant height, canopy volume, mean leaf area, and number of new shoots per plant but had no effect on trunk diameter, number of leaf per new shoot and new shoot diameter. Flowering phenology was also altered by AM infection. The infected plants produced more flowers which despite abscission caused an increase in the initial number of fruits. AM inoculation increased plant phosphorous in T3, potassium in T1, T2, T3, calcium in T2, T3, T4, and the AM-nutrient relationship did not reveal any generalized pattern. Inoculated plants, however, had higher concentration of different elements by the second year of the experiment indicating towards the continuous and cumulative effect of AM infection on plant nutrient accumulation. Further, the beneficial effects of AM on Kinnow were not related to the difference in the species of mycorrhiza.

Ectomycorrhizae, arbuscular mycorrhizae, and dark-septate fungi on Salix humboldtiana in two riparian populations from central Argentina

Colonization of Salix humboldtiana (Salicaceae) by ectomycorrhizae (ECM), arbuscular mycorrhizae (AM), and dark-septate endophytic (DSE) fungi was studied throughout autumn on two riparian populations in central Argentina. AM and DSE infection on roots ranged from 0% to 17% and from 2% to 20% respectively, whereas ECM colonization was higher, varying between 33% and 99% for both sites. Seven ECM morphotypes were found on S. humboldtiana roots. The nuclear rDNA internal transcriber spacer (ITS) region from the ectomycorrhizal root tips was amplified using ITS-1F and ITS-4 primers. Two of the seven ECM types were identified by searching GenBank blasts: one attributed to the genus Tomentella (Thelephoraceae) and the second most closely matched to Inocybe sp. (Cortinariaceae). The ECM colonization varied among sampling dates and sites, whereas AM and DSE colonization varied only among sampling dates. Diversity values for the ECM morphotype were not significantly different for autumn months or among the two sites. Positive correlations were found between Inocybe sp. and sites and between Inocybe sp., Tomentella sp., morphotypes III, IV, and VI, and sampling dates. This article provides the first documented evidence of co-occurrence of ECM, AM, and DSE in S. humboldtiana.

Ectomycorrhizae, arbuscular mycorrhizae, and dark-septate fungi on <i>Salix humboldtiana</i> in two riparian populations from central Argentina

Colonization of Salix humboldtiana (Salicaceae) by ectomycorrhizae (ECM), arbuscular mycorrhizae (AM), and dark-septate endophytic (DSE) fungi was studied throughout autumn on two riparian populations in central Argentina. AM and DSE infection on roots ranged from 0% to 17% and from 2% to 20% respectively, whereas ECM colonization was higher, varying between 33% and 99% for both sites. Seven ECM morphotypes were found on S. humboldtiana roots. The nuclear rDNA internal transcriber spacer (ITS) region from the ectomycorrhizal root tips was amplified using ITS-1F and ITS-4 primers. Two of the seven ECM types were identified by searching GenBank blasts: one attributed to the genus Tomentella (Thelephoraceae) and the second most closely matched to Inocybe sp. (Cortinariaceae). The ECM colonization varied among sampling dates and sites, whereas AM and DSE colonization varied only among sampling dates. Diversity values for the ECM morphotype were not significantly different for autumn months or among the two sites. Positive correlations were found between Inocybe sp. and sites and between Inocybe sp., Tomentella sp., morphotypes III, IV, and VI, and sampling dates. This article provides the first documented evidence of co-occurrence of ECM, AM, and DSE in S. humboldtiana.

Indigenous arbuscular mycorrhiza is more important for early growth period of groundnut (Arachis hypogea L.) for P influx in an Oxisol

The contribution of indigenous arbuscular mycorrhiza (AM) on phosphorus (P) uptake by groundnut was examined in a low P field soil. The fungicide benomyl was applied to eradicate mycorrhizal infection. The treatments consisted of three P levels viz. 0, 50 and 400 mg P kg-1 soil, with and without benomyl application. Groundnut as test crop was sown two weeks after the application of benomyl and was harvested four times covering the whole growth period. At each harvest, the shoot yield, shoot P concentration, root length, soil solution P (CLi) and per cent root infection by AM was determined for benomyl treated and untreated soil at all P levels. Benomyl showed no effect on soil solution P concentration. When P was limiting, application of benomyl did reduce early groundnut growth by 40-50% at P-0, and by 25-30% at P-50. At high P supply (P-400), benomyl had little or no effect on dry matter production. Thus, indicate that the effect of benomyl on plant growth was by its influence on P uptake from soil. Phosphorus supply affected percentage of root infected by AM which was 40% of the roots at P-0, and decreased to around 30% and 10% at P-50 and P-400. In the early growing season, the P influx of maize was dependent on P in soil solution and the effect of AM was rather large. At high P supply, the contribution of AM to P influx showed a decrease. Without or low AM infection and at low P level, the P influx was 62% of that with AM. During early growth period groundnut showed a similar behaviour as maize at middle growth stage and without AM reduction of P influx, which was to an extent of 67%. In absolute terms AM is more important at maximum growth in the early growth season for groundnut. It is evident from the present investigation that AM may make an significant contribution by about 35 % to the P nutrition of groundnut, but other factors, like P solubilization by root exudates, may be even more important.

Indigenous arbuscular mycorrhiza is more important for early growth period of groundnut (Arachis hypogea L.) for P influx in an Oxisol

The contribution of indigenous arbuscular mycorrhiza (AM) on phosphorus (P) uptake by groundnut was examined in a low P field soil. The fungicide benomyl was applied to eradicate mycorrhizal infection. The treatments consisted of three P levels viz. 0, 50 and 400 mg P kg -1 soil, with and without benomyl application. Groundnut as test crop was sown two weeks after the application of benomyl and was harvested four times covering the whole growth period. At each harvest, the shoot yield, shoot P concentration, root length, soil solution P (CLi) and per cent root infection by AM was determined for benomyl treated and untreated soil at all P levels. Benomyl showed no effect on soil solution P concentration. When P was limiting, application of benomyl did reduce early groundnut growth by 40-50% at P-0, and by 25-30% at P-50. At high P supply (P-400), benomyl had little or no effect on dry matter production. Thus, indicate that the effect of benomyl on plant growth was by its influence on P uptake from soil. Phosphorus supply affected percentage of root infected by AM which was 40% of the roots at P-0, and decreased to around 30% and 10% at P-50 and P-400. In the early growing season, the P influx of maize was dependent on P in soil solution and the effect of AM was rather large. At high P supply, the contribution of AM to P influx showed a decrease. Without or low AM infection and at low P level, the P influx was 62% of that with AM. During early growth period groundnut showed a similar behaviour as maize at middle growth stage and without AM reduction of P influx, which was to an extent of 67%. In absolute terms AM is more important at maximum growth in the early growth season for groundnut. It is evident from the present investigation that AM may make an significant contribution by about 35 % to the P nutrition of groundnut, but other factors, like P solubilization by root exudates, may be even more important.

Effects of arbuscular mycorrhiza and phosphorus application on arsenic toxicity in sunflower (Helianthus annuus L.) and on the transformation of arsenic in the rhizosphere

Effects of arbuscular mycorrhiza (AM) and phosphorus (P) application on arsenic (As) toxicity were studied in a rhizobox system with As-contaminated soil collected from Shimane Prefecture, Japan. The treatments consisted of a combination of two levels of AM (Glomus aggregatum) inoculation (−AM and +AM) and two levels of P application (−P and +P at 30 mg P kg−1). Sunflower (Helianthus annuus L.) seedlings were cultured in rhizoboxes for 6 weeks. Rates of root AM infection in +AM treatments were about 40% regardless of P application. AM inoculation as well as P application reduced As toxicity symptoms, most clearly so in the +AM−P treatment. Plant growth was highest in the +AM + P treatment. Shoot As concentrations were slightly reduced by AM inoculation but enhanced by P application. Shoot P concentration in the +AM−P treatment was similar to that of +P treatments and was higher than in −AM−P. Analyses of rhizosphere soils at the end of the cultivation period indicated that P application increased water-soluble As (WS−As) in all compartments while AM inoculation increased WS−As in the central compartment only. Both the WS−arsenite [WS−As(III)] and the dominant form, arsenate [WS−As(V)], showed gradients toward the root surface. Dimethylarsine (DMAA) was detected in the +AM treatments only. To our knowledge, this is the first report of the occurrence of DMAA in the mycorrhizosphere. AM inoculation increased WS−P similarly as +P treatments did and promoted acid phosphatase activity in the soil. In conclusion, AM inoculation alleviated the effects of As toxicity by improving P nutrition without increasing As concentrations in the shoots. Moreover, AM appeared to be involved in the transformation of soil inorganic As into less toxic organic forms.

Seedling growth of two pioneer tropical tree species in Competition: The role of arbuscular mycorrhizae

The effects of arbuscular mycorrhizae (AM) fungi on growth and survival of two pioneer tropical plant species were studied in a greenhouse experiment for 6 months. One, an early pioneer species (Heliocarpus appendiculatus Turcz., Tiliaceae) and the second, a late pioneer species (Stemmadenia donnell-smithii (Rose) Woodson, Apocynaceae). Three growing conditions were used as competition factors—no competition, with intraspecific and interspecific competitions—along with two different conditions of AM—with and without mycorrhizal inoculum. Mycorrhizal colonization of H. appendiculatus roots was seven-fold more than in S. donnell-smithii. With AM infection, H. appendiculatus did not increase in growth, but showed greater survival in the absence of competition. S. donnell-smithii grew better in the presence of AM fungi and the effect of competition was diminished. S. donnell-smithii with AM fungi infection showed better survival and increase in biomass, making it a better competitor than H. appendiculatus.

MASS PROPAGATION OF ECHINACEA ANGUSTIFOLIA: A PROTOCOL REFINEMENT USING SHOOT ENCAPSULATION AND TEMPORARY IMMERSION LIQUID SYSTEM

ISHS XXVI International Horticultural Congress: The Future for Medicinal and Aromatic Plants MASS PROPAGATION OF ECHINACEA ANGUSTIFOLIA: A PROTOCOL REFINEMENT USING SHOOT ENCAPSULATION AND TEMPORARY IMMERSION LIQUID SYSTEM

Cereal/legume rotations affect chemical properties and biological activities in two West African soils

A more widespread use of cereal/legume rotations has been suggested as a means to sustainably meet increasing food demands in sub-Saharan West Africa. Enhanced cereal yields following legumes have been attributed to chemical and biological factors such as higher levels of mineral nitrogen (Nmin) and arbuscular mycorrhizae (AM) but also to lower amounts of plant parasitic nematodes. This study was conducted under controlled conditions to examine the relative contribution of AM, plant parasitic nematodes and increased nitrogen (N) and phosphorus (P) availability to cereal/legume rotation effects on two West African soils. Sample soils were taken from field experiments at Gaya (Niger) and Fada (Burkina Faso) supporting continuous cereal and cereal/legume rotation systems and analysed for chemical and biological parameters. Average increases in cereal shoot dry matter (DM) of rotation cereals compared with continuous cereals were 490% at Gaya and 550% at Fada. Shoot P concentration of rotation millet was significantly higher than in continuous millet and P uptake in rotation cereals was on average 62.5-fold higher than in continuous cereals. Rotation rhizosphere soils also had higher pH at both sites. For the Fada soil, large increases in Bray1-P and organic P were observed in bulk and rhizosphere soils. Plant parasitic nematodes in roots of continuous cereals were 60–80-fold higher than in those of rotation cereals. In both cropping systems mycorrhizal infection rates were similar at 37 days after sowing (DAS) but at 57 DAS AM infection was 10–15% higher in rotation sorghum than in continuous sorghum. This study provides strong evidence that cereal/legume rotations can enhance P nutrition of cereals through improved soil chemical P availability and microbiologically increased P uptake.

Cereal/legume rotation effects on cereal growth in Sudano-Sahelian West Africa: soil mineral nitrogen, mycorrhizae and nematodes.

Yield increases of cereals following legumes in rotation have been previously reported for West Africa, but little progress has been made to explain the mechanisms involved. At four sites in Niger and Burkina Faso, field trials with pearl millet (Pennisetum glaucum (L.) R. Br.), cowpea (Vigna unguiculata (L.) Walp), sorghum (Sorghum bicolor (L.) Moench) and groundnut (Arachis hypogaea L.) were conducted from 1996 to 1998 to investigate the role of soil mineral nitrogen (Nmin), native arbuscular mycorrhizae (AM) and nematodes in cereal/legume rotations. Grain and total dry matter yields of cereals at harvest were increased by legume/cereal rotations at all sites. Soil Nmin levels in the topsoil were consistently higher in cereal plots previously sown with legumes (rotation cereals) compared with plots under continuous cereal cultivation. However, these rotation effects on Nmin were much larger with groundnut than with cowpea. Roots of rotation cereals also had higher early AM infection rates compared to continuous cereals. The dominant plant-parasitic nematodes found in all experiment fields were Helicotylenchus sp., Rotylenchus sp. and Pratylenchus sp. In sorghum/groundnut cropping systems, nematode densities were consistently lower in rotation sorghum compared to continuous sorghum. Continuous groundnut had the lowest nematode densities indicating that groundnut was a poor host for the three nematode groups. In millet/cowpea cropping systems with inherently high nematode densities, crop rotations barely affected nematode densities indicating that both crops were good hosts. These results suggest that on the nutrient poor Sudano-Sahelian soils of our study, total dry matter increases of rotation cereals compared with continuous cereals can be explained by higher Nmin and AM infection levels early in the season. The site-specific magnitude of these effects may be related to the efficiency of the legume species to suppress nematode populations and increase plant available N through N2-fixation.

Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions

A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production.

Influence of compaction from wheel traffic and tillage on arbuscular mycorrhizae infection and nutrient uptake by Zea mays

Interactive effects of seven years of compaction due to wheel traffic and tillage on root density, formation of arbuscular mycorrhizae, above-ground biomass, nutrient uptake and yield of corn (Zea mays L.) were measured on a coastal plain soil in eastern Alabama, USA. Tillage and soil compaction treatments initiated in 1987 were: 1) soil compaction from tractor traffic with conventional tillage (C,CT), 2) no soil compaction from tractor traffic with conventional tillage (NC,CT), 3) soil compaction from tractor traffic with no-tillage (C,NT), and, 4) no soil compaction from tractor traffic with no-tillage (NC,NT). The study was arranged as a split plot design with compaction from wheel traffic as main plots and tillage as subplots. The experiment had four replications. In May (49 days after planting) and June, (79 days after planting), root biomass and root biomass infected with arbuscular mycorrhizae was higher in treatments that received the NC,NT treatment than the other three treatments. In June and July (109 days after planting), corn plants that received C,CT treatment had less above-ground biomass, root biomass and root biomass infected with mycorrhizae than the other three treatments. Within compacted treatments, plants that received no-tillage had greater root biomass and root biomass infected with mycorrhizae in May and June than plants that received conventional tillage. Corn plants in no-tillage treatments had higher root biomass and root biomass infected with mycorrhizae than those in conventional tillage. After 7 years of treatment on a sandy Southeastern soil, the interactive effects of tillage and compaction from wheel traffic reduced root biomass and root biomass infected with mycorrhizae but did not affect plant nutrient concentration and yield. ei]J H Graham

Interspecific competition and arbuscular mycorrhiza: Importance for the coexistence of two calcareous grassland species

Two naturally coexisting grassland species—Centaurea jacea (often predominating) andFragaria vesca (subordinate) were grown together in a pot experiment of factorial design, where competition and arbuscular mycorrhiza (AM) inoculation were used as treatments. The effects of competition were one-sided, i.e. the mass ofF. vesca decreased relatively more than that ofC. jacea as a result of competition. The root and total mass ofC. jacea increased with AM inoculation whileF. vesca did not respond. The mass difference betweenC. jacea andF. vesca in a particular pot increased when plants were mycorrhizal, mostly due to the mass increase ofC. jaceae. This can be explained by the differential response of these species to AM. We did not find any indirect indication of the interplant transfer of resources. The results of this experiment show the more unbalanced competition (larger differences in biomass) resulting from AM infection of plants. *** DIRECT SUPPORT *** A02DO006 00010