The Glycine–Glomus–Rhizobium symbiosis. IV. Interactions between the mycorrhizal and nitrogen-fixing endophytes

Abstract Soybean (Glycine max (L.) Men) plants were grown under controlled conditions in an experiment designed as a 4 × 4 factorial. The factors were N or P nutrition, with different strains of Rhizobium japonicum or N-fertilization as levels of the first factor and different species of vesicular-arbuscular mycorrhizal (VAM) fungi or P fertilization as levels of the other. Organisms used were R. japonicum strains USDA 110, USDA 136, and 61A118, and the VAM fungi Glomus versiforme (Karst.) Berch, Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. and Trappe, and Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. There were 16 treatments: nine Rhizobium + Glomus combinations, three Rhizobium + V and three Glomus+ N combinations, and one non-symbiotic set of plants supplied with N + P. The tripartite symbioses were evaluated by analysis of variance against the Rhizobium + P and Glomus + N comparison treatments for effects on root and leaf dry mass, root N and P content, nodule mass and activity, and VAM colinization. Significant to highly significant main effects and interactions were found in virtually all evaluations due to both Rhizobium strain and VAM–fungal species. We conclude that different endophyte isolates affect not only the host plant, but also the development and function of their co-endophytes. These findings establish the existence of inter-endophyte compatibility, an important consideration when selecting or engineering for desirable endophyte traits.     

The Vesicular Arbuscular Mycorrhiza Associated with Three Cultivars of Rice (Oryza sativa L.)

The present study deals with the occurrence of vesicular arbuscular mycorrhizal fungi in three cultivars of rice in Barak valley. Three cultivars of rice were Pankaj, Malati and Ranjit. The results revealed the association of VAM fungi in all the cultivars of rice. The association was maximum in Pankaj cultivar followed by Malati, and Ranjit, respectively, in all the three sampling phases. All the three cultivars of rice crop showed maximum soil spore population and number of VAM fungal species at the harvesting phase (135 DAS) and minimum at the phase of maturation (90 DAS). Glomus species were found dominating followed by Acaulospora species. Glomus microcarpum, Glomus claroideum, Glomus mosseae and Acaulospora scrobiculata were found in all the three fields.     

Characteristic responses of three tropical legumes to the inoculation of two species of VAM fungi in Andosol soils with different fertilities

The growth and mineral nutrition responses were evaluated of three tropical legumes, cowpea (Vigna unguiculata L. cv Kuromame), pigeonpea [Cajanus cajan L. (Millsp.) cv ICPL 86009] and groundnut (Arachis hypogaea cv Nakateyutaka) inoculated with two different species of VAM fungi, Glomus sp. (Glomus etunicatum-like species) and Gigaspora margarita, and grown in Andosols with different fertilities [Bray II-P: topsoil (72 ppm), subsoil (<0.1 ppm)]. Percent fungal root colonization was high in cowpea and groundnut but relatively low in pigeonpea in both soil types. Despite the low rate of root infection, significant growth responses were produced, especially in the inoculated pigeonpea plant. In all legumes, shoot dry matter production was favoured by the inoculations. Increases in shoot biomass due to mycorrhizae were greater in the subsoil than in the topsoil. Mycorrhization raised shoot concentrations of P and Ca (in cowpea and groundnut) and P and K (in pigeonpea) in the topsoil. Whereas the P concentration in shoots in the subsoil was not positively affected by VAM fungi, particularly in cowpea and pigeonpea, the concentration of K in such plants was significantly increased by VAM treatment. The results also showed that mycorrhizal enhancement of shoot micronutrient concentrations was very rare in all plants, with negative effects observed in certain cases. Cu concentration, in particular, was not affected by VAM formation in any of the plants, and Mn and Fe in pigeonpea and groundnut, respectively, remained the same whether plants were mycorrhizal or not. In both soils the three legumes responded to Glomus sp. better than to Gigaspora margarita, and the effects of the VAM fungi on each of the crops relative to the controls were greater in the subsoil than in the topsoil. However, shoot growth of groundnut was not affected as much as cowpea and pigeonpea by the type of soil used. In spite of the relatively low infection of its root, pigeonpea was generally the most responsive of the three legume species in terms of mycorrhizal/nonmycorrhizal ratios.     

Host genotype dependency and growth enhancing ability of VA-mycorrhizal fungi for Eleusine coracana (finger millet)

Inoculation of finger millet (Eleusine coracana Gaertn.) plants with one of six different vesicular, arbuscular, mycorrhizal (VAM) fungi increased plant biomass, height, leaf area and absolute growth rate; however, effectiveness of the various VAM fungi varied significantly. Maximum root colonization and mycorrhizal efficacy was observed with plants inoculated with Glomus caledonicum. Among five host genotypes tested for mycorrhizal dependency against G. caledonicum, genotype HR-374 gave the highest plant biomass, mycorrhizal efficacy and root colonization, the inoculation resulting in increased mineral (phosphate, nitrogen, Zn²⁺ and Cu²⁺) content and uptake in shoots.     

Compatibility and Coselection of Vesicular-Arbuscular Mycorrhizal Fungi and Rhizobia for Tropical Legumes

Abstract

The effect of dual inoculation on three local cultivars (Miss Kelly, Portland Red, Round Red) of red kidney bean (Phaseolus vulgaris, L.) with four strains of Rhizobium phaseoli (B36, B17, T2, and CIAT652) and three species of vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus pallidum, Glomus aggregatum, and Sclerocystis microcarpa) was examined in sterilized and nonsterilized soil. Symbiotic efficiency (improved plant growth response and enhanced nitrogen (N) and phosphorus (P) nutrition) was dependent on the particular combination of Rhizobium strain, VAM fungus, and cultivar of kidney bean. Whereas rhizobial strains B36 and B17 paired with G. pallidum or G. aggregatum showed increased growth response of cv. Miss Kelly and Portland Red, rhizobial strain T2 paired with any of the three VAM fungi was the best compatible pairing for the cv. Round Red. It is suggested that even though dual inoculation significantly improves the growth response of the bean, the best pairings of VAM fungus and rhizobia for legumes is a question to be carefully examined.     

The effect of soil phosphorus on the external mycelium growth of arbuscular mycorrhizal fungi during the early stages of mycorrhiza formation

The effects of soil P amendments and time of application on the formation of external mycelium by different arbuscular mycorrhizal (AM) fungi were studied. In the first experiment the external mycelium produced in the soil by the AM fungus Glomus etunicatum Beck. and Gerd., during the early stages of root colonization (7 and 14 days after inoculation), was quantified by the soil-agar film technique. A Brazilian Oxisol was used with three different phosphate levels, varying from deficient to supra-optimal for the plant. Significant differences were observed in the phosphate and inoculation treatments for plant dry weight, P content in the tissue, root length and root colonization, at fourteen days after planting. At 7 days, mycelium growth, root colonization and their relationship were reduced at supra-optimal P concentrations. Applications of P one week after planting reduced mycelium growth and root colonization more than when applied to the soil before planting. In a second experiment the arbuscular mycorrhizal (AM) fungi, Scutellospora heterogama (Nicol. and Gerd.) Walker and Sanders and E3 were tested and compared with Glomus etunicatum. For the species studied, the length of external hyphae per unit of colonized root length was affected by small P additions but no further significant differences were observed at high P levels. The three AM endophytes showed marked differences in their response to P in the soil: Scutellospora heterogama, although producing external mycelium more profusely than the Glomus spp., showed a higher sensitivity to soil P supply.     

Influence of three vesicular-arbuscular mycorrhizal fungi (Glomaceae) on the activity of specific enzymes in the root system of Cucumis sativus L.

The influence of three vesicular-arbuscular mycorrhizal (VAM) Glomus species on the activity of enzymes in the roots of Cucumis sativus was tested. Cucumber plants were grown in a split-root system, in which colonized and uncolonized roots of a single plant could be separated. The activity of the host root malate dehydrogenase (MDH), glucose 6-phosphate dehydrogenase (Gd), glutamate oxaloacetate transaminase (GOT) and glutamate dehydrogenase (GDH) was measured on a densitometer after separation of the host and fungal enzymes on polyacrylamide gels.The results showed that only minor changes in the activity of the host root enzymes occurred after VAM inoculation. Gd was stimulated by VAM and phosphorus, and one of the fungi decreased the activity of GDH in the host plant when both parts of the root system were colonized.     

Growth and nutrient uptake of sorghum cultivated with vesicular-arbuscular mycorrhiza isolates at varying pH

This study was conducted to determine the effects of different pH regimes on root colonization with four vesicular-arbuscular mycorrhiza (VAM) isolates, and VAM effects on host plant growth and nutrient uptake. Sorghum [Sorghum bicolor (L.) Moench] was grown at pH 4.0, 5.0, 6.0 and 7.0 (±0.1) in hydroponic sand culture with the VAM isolates Glomus etunicatum UT316 (isolate E), G. intraradices UT143 (isolate I), G. intraradices UT126 (isolate B), and an unknown Glomus isolate with no INVAM number (isolate A). Colonization of roots with the different VAM isolates varied differentially with pH. As pH increased, root colonization increased with isolates B and E, remained unchanged with isolate I, and was low at pH 4.0 and high at pH 5.0, 6.0, and 7.0 with isolate A. Isolates E and I were more effective than isolates A and B in promoting plant growth irrespective of pH. Root colonization with VAM appeared to be independent of dry matter yields or dry matter yield responsiveness (dry matter produced by VAM compared to nonmycorrhizal plants). Dry matter yield responsiveness values were higher in plants whose roots were colonized with isolates E and I than with isolates A and B. Shoot P concentrations were lower in plants colonized with isolates E and I than with isolates A and B or nonmycorrhizal plants. This was probably due to the dilution effect of the higher dry matter yields. Neither the VAM isolate nor pH had an effect on shoot Ca, Mg, Zn, Cu, and Mn concentrations, while the VAM isolate affected not only P but also S, K, and Fe concentrations. The pH x VAM interaction was significant for shoot K, Mg, and Cu concentrations.     

Infection by the VA-mycorrhizal fungusGlomus caledonium inHedysarum coronarium as influenced by host plant and P content of soil

The low degree of infection ofHedysarum coronarium L. (sulla) exposed to inoculum of the VAM endophyteGlomus caledonium was investigated. Infection began after a prolonged lag phase and remained at very low levels even after three months’ growth. Neither very high rates of inoculum, nor very low P content of the soil raised the low infection level of the sulla plants. There appeared to be some differences in rate of infection among ten different ecotypes of sulla but the level of infection remained low in all cases. In all tested populations some plants remained uninfected. The low infection rate of sulla may therefore have a genetic basis. It was shown that the growth ofH. coronarium is hardly improved by phosphate fertilization. This may explain the poor response of this plant species, adapted to grow in nutrient-deficient soil, to VAM. Programmes aimed at increasing the productivity in marginal soils through the introduction of efficient VAM endophytes should take into account the fact that certain plant species growing in marginal soils may not always benefit from mycorrhizal inoculation, due to their inherently low mycorrhizal dependency.     

A comparison of wild-type, old and modern tomato cultivars in the interaction with the arbuscular mycorrhizal fungus Glomus mosseae and the tomato pathogen Fusarium oxysporum f. sp. lycopersici

The effect of the arbuscular mycorrhizal symbiosis (AM) varies in plant cultivars. In the present study, we tested whether wild-type, old and modern tomato cultivars differ in the parameters of the AM interaction. Moreover, the bioprotective effect of AM against the soilborne tomato pathogen Fusarium oxysporum f. sp. lycopersici (Fol) was tested in the different cultivars. Ten tomato cultivars were inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus mosseae alone or in combination with Fol. At the end of the experiment, AM root colonization, Fusarium infection, and the plant fresh weight was determined. The tomato cultivars differed in their susceptibility to AMF and Fol, but these differences were not cultivar age dependent. In all the cultivars affected by Fol, mycorrhization showed a bioprotective effect. Independent of the cultivar age, tomato cultivars differ in their susceptibility to AMF and Fol and the bioprotective effect of mycorrhization, indicating that the cultivar age does not affect the AM parameters tested in this study.     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

Effect of aromatic plant species on vesicular-arbuscular mycorrhizal establishment in Pistacia terebinthus

The inoculation of Pistacia terebinthus with vesicular-arbuscular mycorrhizal (VAM) fungi and the spread of the infection were studied using a mixed cropping system, under glasshouse conditions, with Salvia officinalis, Lavandula officinalis and Thymus vulgaris colonized by Glomus mosseae as an inoculation method. This method was compared with soil inoculum placed under the seed or distributed evenly in the soil. Indirect inoculation with all the aromatic plants tested significantly increased VAM root colonization of P. terebinthus compared with the use of soil inoculum, although the effect on plant growth was different for each one of the aromatic species used as inoculum source. Inoculation with L. officinalis and T. vulgaris were the best treatments resulting in high VAM colonization and growth enhancement of P. terebinthus.     

Mycorrhizal dependency of banana (Musa acuminata,AAA group) cultivar

Seven banana cultivars (Musa acuminata, AAA group) were inoculated with two species of vesicular arbuscular mycorrhizal (VAM) fungi (Glomus mosseae and Glomus macrocarpum) in a greenhouse experiment. Inoculated plants had generally greater shoot dry weight and shoot phosphorus concentrations compared to the noninoculated plants. A great variation in dependency on mycorrhizal colonization was observed among the banana cultivars. Cv. Williams showed the highest relative mycorrhizal dependency (RMD) and cv. Poyo the lowest. For all the cultivars studied, inoculation with G. macrocarpum resulted in the highest RMD values. Both root dry weight and root hair length or density of the noninoculated plants were inverserly correlated with the RMD values of cultivars.     

Receptivity of various wheat cultivars to infection by VA-mycorrhizal fungi as influenced by inoculum potential and the relation of VAM-effectiveness to succinic dehydrogenase activity of the mycelium in the roots

Wheat cultivars grown in pots in a greenhouse were inoculated either once or twice with the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus mosseae. If inoculum was only added to the soil once (before planting) the cultivars showed differences in subsequent VAM development. If additional inoculum was added ten days after planting, VAM development was much increased and cultivars which remained without VAM after only one inoculum application now became mycorrhizal.Succinate dehydrogenase (SDH) activity decreased throughout the experiment, but this decrease was less rapid in mycelium in twice-inoculated plants.No close relationship between SDH-activity and plant growth (VAM effectiveness) was found.     

Rapid methods for quantifying VAM fungal infections in maize roots

Roots of maize (Zea mays cv W64A × W182E) infected by vesicular arbuscular mycorrhizal (VAM) fungi (Glomus versiforme (Karst) Berch or a Glomus species isolated from an alfalfa soil) exhibit a bright yellow pigmentation. The percentage of pigmented roots can be quantified by a rapid visual estimate or by a grid intersect method. Both methods gave similar estimates of VAM infection to those obtained using a grid intersect count on cleared roots stained with chlorazol black E. Thus for experimental or field evaluation where speed and quantity are important, the rapid visual estimate (less than one minute for each washed root system) yields reliable results. The yellow root intersect method takes longer (5–15 minutes per root system) but gives more reproducible results. The yellow root pigmentation is light sensitive However, root systems can be reliably assayed after 1 week when stored at 5°C in the dark or after 1 year if dried.     

The mycorrhizal status of the woody Mediterranean shrub Myrtus communis L.

  Myrtus communis L. (myrtle), a typical Mediterranean plant species belonging to the family Myrtaceae, was shown to form arbuscular mycorrhizal symbioses in nature. Many different spore types were isolated from its rhizosphere and grown in pot cultures; six of them were identified as Glomus species. In the laboratory, the myrtle root system was colonized by indigenous endophytes as well as by an Italian isolate of Glomus intraradices. In greenhouse experiments, mycorrhizal inoculation reduced transplant stress in 60-day-old myrtle seedlings; their growth was renewed immediately after transplanting, whereas non-mycorrhizal plants stopped development. Significantly larger growth responses were obtained using indigenous fungi than the Italian isolate of Glomus intraradices. Accepted: 16 January 1997     

Effects of vesicular-arbuscular mycorrhizal inoculation at different soil P availabilities on growth and nutrient uptake of in vitro propagated coffee (Coffea arabica L.) plants

 In a pot experiment, the growth and the nutrient status of in vitro propagated coffee (Coffea arabica L.) microcuttings were investigated for 5 months following vesicular-arbuscular mycorrhizal (VAM) inoculation with either Acaulospora melleae or Glomus clarum at four soil P availabilities. Control plants remained P-deficient even at the highest soil P availability while mycorrhizal plants were P-sufficient at all soil P availabilities. Growth of control plants was only improved at the highest soil P availability. In P-deficient soil, neither of the two VAM species improved plant growth. Plant growth increased by 50% following inoculation with either A. melleae or G. clarum when P availability went from deficient to low. No further plant growth improvement was induced by either VAM species at intermediate and high soil P levels. Nevertheless, growth of plants inoculated with G. clarum was still significantly greater than that of non-mycorrhizal plants at the highest soil P availability. Root colonization by G. clarum increased with increasing soil P availability while root colonization by A. mellea decreased with soil P level increasing above low P availability. Soil P availability also affected Zn nutrition through its influence on VAM symbiosis. With increasing soil P availability, foliar Zn status increased with G. clarum or decreased with A. mellea in parallel to root colonization by VAM. This study demonstrates the beneficial effects of VAM inoculation on in vitro propagated Arabica coffee microcuttings, as shown previously for seedlings. This study also demonstrates differences in tolerance to soil P availability between VAM species, most likely resulting from their differing abilities to enhance coffee foliar P status. Accepted: 14 November 1996     

Effect of soybean plant growth on spore production byGlomus mosseae

Plants of two soybean cultivars infected withGlomus mosseae were physiologically stressed by top removal and were harvested at seven bi-weekly intervals. Removing tops stopped root growth, stimulated branching, delayed plant growth stages by approximately two weeks, but did not affect spore production. Spore numbers were significantly related only to time of harvest. Pot variation in spore number was not significantly correlated with infection percentage or root dry weight. Harvest, cultivar, and cutting effects were highly significant for root and shoot weights and root/shoot ratios.Approved by the Director as a contribution from the Missouri Agricultural Experiment Station (Journal Series No. 8123).     

Mineral and lipid composition of Glycine - Glomus - Bradyrhizobium symbioses

Soybean [Glyeine max (L.) Merr. cv. Amsoy 71] plants were inoculated with either the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum. with a strain of Bradyrizobobium Japonicum. or with both endophytes in combintion. Noninoculated controlplantes were fertilized with levels of N and P previously found to compensate for nutrient input following infection by Bradyhizobium or Glomus Temporal differences in N and P assimilation in nodulated or mycorrhizal plants indicated that Glomus was most effective during early vegetative growth and Bradyrhizobion was active until the mid-pod-fill stage in soybean. In general. soybeans colonized by Glomus contained more Cu but less Mn and P than corresponding P-fertilized plants. Soyubean roots infected with G. fasciculaum contained five unusual fatty acids: [16: 1 (11c): 8:3 (6c, 9c, 12c): 20:3 (8c, 11c, 14c): 20:4 (5c, 8c, 11c, 14c): 20:5 (5c, 8c, 11c, 14c, 17c)] that were absent in non-infected roots. Fatty acid 16:1 (11c) comprised 43% of total fatty acids in Glomus-infected roots at week 9 and 29% of total root fatty acids at week 15. This isomer of hexadecenoic acid was positively correlated with vesicle number (r = 0.92**). and 16:1 (11c) was probably the principalstorage fatty acid in fungal vesicles. These five unusual fatty acids were not found in the leaves. pods or seeds of either VAM or non-VAM plants. Specific leaf area increased with time in nodulated soybeans. but these plants contained lessCu than corresponding N-fertilized plants. Soybeans nodulated with Bradyrthizobium contained more total lipid and proportionately more fatty acid 16:0 than N-fertilized plants. Infection by Glomus or Bradyrhizobium also altered the fatty acid composition of above-ground plant parts, although these changes were subtle compared to the markedly different fatty acid found in Glomus-infected roots. These findings suggest that seed quality may be altered due to the physiological changes resulting from infection by N²-fixing bacteria and/or endomycorrhizal fungi. Observed differences in the plant nutrition of inoculated soybeans could not be replicated by fertilizer addition alone.     

Effects of species of VA-mycorrhizal fungi on growth and mineral uptake of sorghum at different temperatures

Sorghum [Sorghum bicolor (L.) Moench] plants were grown in growth chambers at 20, 25 and 30°C in a low P Typic Argiudoll (3.65 µg P g^–1 soil, pH 8.3) inoculated with Glomus fasciculatum, Glomus intraradices, and Glomus macrocarpum to determine effects of vesicular-arbuscular mycorrhizal fungi (VAMF) species on plant growth and mineral nutrient uptake. Sorghum root colonization by VAMF and plant responses to Glomus species were temperature dependent. G. macrocarpum colonized sorghum roots best and enhanced plant growth and mineral uptake considerably more than the other VAMF species, especially at 30°C. G. fasciculatum enhanced shoot growth at 20 and 25°C, and mineral uptake only at 20°C. G. intraradices depressed shoot growth and mineral uptake at 30°C. G. macrocarpum enhanced shoot P, K, and Zn at all temperatures, and Fe at 25 and 30°C above that which could be accounted for by increased biomass. Sorghum plant growth responses to colonization by VAMF species may need to be evaluated at different temperatures to optimize beneficial effects.