Vesicular-arbuscular Mycorrhiza Fungi Research Articles

Heavy ion and proton beams in high resolution imaging of a fungi spore specimen using STIM tomography

Scanning transmission ion microscopy (STIM) tomography as a 3-D imaging technique has been shown to have a range of applications. The energy of the transmitted ion is detected with nearly 100% efficiency as a function of position in the transverse plane. The parameters relating to transmitted ion energy loss in the sample are imaged with statistics given by the energy loss process rather than Poisson counting statistics. This enables very fast collection of a set of relatively noise-free 2-D images. Each image is collected after a small rotation of the sample, and a complete 3-D representation of the sample may be tomographically reconstructed. The small beam currents necessary mean that the technique is non-destructive. One of the fields where these non-destructive 3-D density structure maps are particularly useful is in the analysis of biological tissue. The variation of energy loss with projectile atomic number may be exploited to tune the energy loss contrast to the size and density of the sample (heavy ion STIM). This work develops this point, and applies it to the imaging of the microscopic structure of a 90 μm diameter mycorrhiza fungi spore. This specimen has been imaged non-destructively in 3-D using both a 36 MeV 12C beam and a 2.2 MeV proton beam, both with a spatial resolution of about 1 μm. The gain in contrast in the carbon median energy loss maps was dramatic as expected. The corresponding improvement in the tomogram was found to be visible but less dramatic. The tomographic sections as well as the median energy loss maps of the vesicular-arbuscular mycorrhiza fungi spore clearly show the internal structure. Wall morphology data has relevance to germination behaviour of the spores.

Effect of VA mycorrhizas on phosphorus uptake and growth of white clover (Trifolium repensL.) growing in association with ryegrass (Lolium perenneL)

Abstract In a phosphorus‐deficient soil, vesicular‐arbuscular mycorrhizas (VAM) helped white clover to compete more effectively with ryegrass for phosphate, resulting in better phosphate acquisition by mycorrhizal clover than non‐mycorrhizal clover. The benefit was greatest when competition from ryegrass was severe. Mycorrhizal clover did not grow much faster than non‐mycorrhizal clover, probably because of competition for light from neighbouring ryegrasses. When the soil was fertilised with phosphate, clover and ryegrass yields increased, and non‐mycorrhizal clover plants outyielded mycorrhizal plants. Similar parasitic effects of VAM have been recorded before. It is concluded that the presence of VAM linkages between clover and grass roots will probably negate any benefits to clover of the introduction of elite VAM fungi to pasture soils. Genetic manipulation of a host plant's response to VAM, may be a more profitable way of improving the phosphate nutrition of white clover in mixed swards.

Grazing preferences of some collembola for endomycorrhizal fungi

The ability of five collembolan species to distinguish and graze selectively on vesicular-arbuscular mycorrhiza (VAM) has been verified. Four species preferred the food infected by VAM fungi. All collembolan species showed more of less significant preferences for one species/isolate of the VAM fungi.

Functional Ecology of Vesicular Arbuscular Mycorrhizas as Influenced by Phosphate Fertilization and Tillage in an Agricultural Ecosystem

The importance of vesicular arbuscular mycorrhizas (VAM) in an agricultural crop production system depends largely on our ability, through soil management, to increase the effectiveness of the indigenous mycorrhizal fungal population. To do so requires a good understanding of the functional ecology of the symbiosis.In this article, we discuss primarily our programs at Guelph, which have focused on two aspects of the symbiosis: the influence of phosphate (P) fertilization on colonization and the influence of soil disturbance by tillage on colonization and P absorption.Although it is generally accepted that the level of colonization of roots by VAM fungi decreases with increased P availability, we have found that the decrease is not as marked as thought. A reasonable degree of colonization was observed at available P levels well above those required for maximum yield. We have also found that the reduction in colonization occurs to a greater extent in the roots growing in a fertilized zone than in those outside this zone. Thus, although a band application of fertilizer may markedly reduce colonization in the fertilized zone, the remainder of the root system would be well colonized, and have an increased ability to acquire phosphorus.That soil disturbance by tillage reduces the effectiveness of the VAM symbiosis in maize was first observed in the early 1980s. Since then we have conducted numerous field and growth chamber experiments to determine the practical importance of this effect in crop production and to elucidate the mechanisms involved. Systems such as no-till and ridge-till have been shown to result in greater P absorption during early maize growth. They also result in earlier colonization in some, but not all, cases. We have not, as yet, observed a yield advantage as a result of the earlier P absorption. This may be because factors other than P nutrition are limiting yields with the reduced tillage systems. Our results do indicate quite clearly, however, that greater rates of P fertilizer are not required in reduced tillage systems, compared with systems that cause a greater degree of soil disturbance. We suggest that lesser rates of P fertilizer may be required, which would have both an economic and environmental impact.Our studies to elucidate the mechanisms have led to the conclusion that the integrity of the extraradical mycelium from a previous crop is a critical factor in the greater early P absorption in undisturbed systems. It may also be important in rapid colonization of roots of newly developing seedlings. This latter effect, however, has been quite inconsistent in our studies. It is apparent that some unknown factor or factors, in addition to the integrity of the mycelium, is also critical.The fact that a preexisting extraradical mycelium is important for early P nutrition under our field conditions led to the hypothesis that the mycelium from a previous crop retains its infectivity and is able to absorb and transport P to newly attached roots following an extensive period during which the soil is frozen. Experiments in which pouches containing soil with a root-free mycelium were exposed to freezing for differing lengths of time have provided evidence to support this hypothesis. Roots growing in undisturbed pouches removed from the field when the soil was frozen were rapidly colonized during a bioassay. Disturbance of the soil in these pouches invariably reduced P absorption by the bioassay plants and sometimes, but not always, reduced colonization.A more thorough understanding of the mechanisms involved in the effect of disturbance on colonization would increase the potential for increasing the effectiveness of the VAM symbiosis in crop production through management practices.

Research approaches to study the functioning of vesicular-arbuscular mycorrhizas in the field

Approaches suitable for the study on the functioning of vesicular-arbuscular mycorrhizas (VAM) in the field are discussed, with emphasis on those VAM-specific processes which may influence P nutrition of crops. These processes are related to hyphal P transport in particular, and conventional techniques based on comparisons between VAM-colonized plants and uncolonized controls are therefore of limited value in such studies. Novel methods are described, which make use of a two-compartment principle and isotopes to directly measure the P transport by the VAM mycelium under controlled conditions and in the field. The principle of isotopic equilibrium may be used for indirectly quantifying the relative amounts of P supplied by hyphae and by roots of VAM plants. The hyphal contribution to P uptake may also be assessed by comparing hyphal uptake of 32P from a hyphal compartment with uptake of 33P from a corresponding compartment containing both roots and hyphae. These methods are suitable for a functional characterization of VAM fungi and for identifying constraints to the functioning of VAM.

Phytotoxicity of Fosetyl Al and Phosphonic Acid to Maize During Production of Vesicular-Arbuscular Mycorrhizal Inoculum

Research into the function of vesicular arbuscular mycorrhizae (VAM) requires production of sufficient quantities of high-quality inoculum. Contamination of one of our Glomus cultures on maize with Pylhhim myrioiylum prompted us to assess the effects of anti-oomycete fungicides on colonization of maize by strains of Glomus mosseae, G. macrocarpum, G. elunicalum, and G. microcarpum. Following mycorrhizal inoculation, partially sterilized soil in pots was treated with fungicides at rates recommended for Pythium control: I) metalaxyl (0.05% Ridomil 250WP, 100 ml per pot as a soil drench, or 2.5 g of Ridomil 50G per 10 L of soil), 2) fosetyl Al (0.1% Aliette 740WP, 200 ml per pot as a soil drench), and 3) phosphonic acid (0.25% Foli-R-Fos 400, 100 ml per pot as a soil drench), all applied before planting the maize. Plants treated with fosetyl Al or phosphonic acid had stunted roots and tops that were rosetted and spindly with white variegated streaking of the leaves, symptomatic of induced zinc deficiency. Percent colonization of the roots was slightly decreased by fosetyl Al and phosphonic acid, but the total length of mycorrhizal root was markedly decreased. Metalaxyl had no phytotoxic effects on maize. Excellent mycorrhizal colonization of the Glomus-inoculated pots was obtained with the metalaxyl treatments, indicating that this fungicide did not adversely affect VAM cultures. Melalaxyl (granular form) is recommended for routine addition to open-pot cultures of VAM fungi on maize.

Distribution of Vesicular-Arbuscular Mycorrhizae in Plants Growing in a River Floodplain.

To study the effects of river flooding on vesicular-arbuscular mycorrhizae (VAM), VAM infection of plants was examined at a fluvial bar in the middle reach of the Ohta River in Hiroshima Prefecture, Japan. Among 23 plant species belonging to 11 families collected in spring and early summer 1993, 17 species showed VAM with arbuscules. The relation between VAM infection and plants' growth stages was investigated in the annual legume Kummerowia striata. VAM infection was observed early in seedlings that had few leaves. Prolonged flooding in the 1993 summer season severely destroyed the vegetation in the study site. However, most of the plants survived the flooding, and those which germinated afterward showed VAM infection. Spores of VAM fungi were found not only in the soils of areas with good vegetation cover but also in the soils of gravelly areas without vegetation. However, spore density and infection level tended to be lower in severely eroded sites.

Vesicular-Arbuscular Mycorrhizal Fungi: A Determinant of Plant Community Structure in Early Succession

1. Infection of plants by vesicular-arbuscular mycorrhizas (VAM) was reduced by application of the contact fungicide iprodione in two early successional plant communities. 2. One community was initiated in 1988 and monitored for four years, the other started in 1990 and monitored for 18 months. 3. In both communities reduction in fungal infection resulted in a lower plant species richness, with a number of species occurring in untreated (control) plots but absent in fungicide-treated plots. These were mostly perennial forbs. 4. It is suggested that VAM fungi are important in structuring early successional communities and that this is brought about by enhanced seedling establishment of forbs when fungi are present

Vesicular-arbuscular mycorrhizae in relation to plant disease

Vesicular-arbuscular mycorrhizae (VAM) enhance plant growth through increased nutrient uptake, stress tolerance and disease resistance. As an integral part of the root system, they interact with other microorganisms in soil and result in increased root exudation approaching about 25% of the plant dry matter production. Roots support a multitude of microorganisms that, in concert, can have profound influence on growth and survival of the plant. VAM fungi can alter the root exudation pattern, enhance chitinolytic activity and alter photosynthetic/respiratory deficiencies. VAM-positive plants are known to exhibit varied resistance towards soil-borne and foliar pathogens. The known interactions include a number of mechanisms, such as exclusion of the pathogen, lignification of plant cell walls, changed phosphate nutrition resulting in altered exudation by roots, and formation of inhibitory low molecular weight compounds. The purpose of this review is to discuss VAM-plant-pathogen interactions and the possible mechanisms involved in altered resistance. Based on these observations, a working model is proposed to explain the VAM-disease interaction under varied environmental conditions.

MYCORRHIZAE IN HAWAIIAN ANGIOSPERMS: A SURVEY WITH IMPLICATIONS FOR THE ORIGIN OF THE NATIVE FLORA

Endemic, indigenous, naturalized and cultivated angiosperms growing in a variety of habitats in Hawaii were examined for mycorrhizae. Of 147 species (representing 61 families) examined, 122 were mycorrhizal, and 98% of the latter formed vesicular‐arbuscular mycorrhizae (VAM). Ericoid, orchid, and ectomycorrhizae also were found. Mycorrhizae were most frequent in endemic species (90.3%) and least in indigenous species (71.9%). The incidence of mycotrophy in Hawaiian endemic species was significantly greater than in mainland species. In addition, VAM often were found in species belonging to families that typically lack mycorrhizae (Aizoaceae, Brassicaceae, Caryophyllaceae, Cyperaceae, Hydrophyllaceae, Juncaceae, Pandanaceae, and Urticaceae). Naturalized weedy species were highly mycorrhizal. The high incidence of mycorrhizae in endemic species suggests that VAM fungi and obligately mycotrophic plant species may have been present in the Hawaiian Islands from the earliest stages of the development of the angiosperm flora.

A field study using the fungicide benomyl to investigate the effect of mycorrhizal fungi on plant fitness.

The effect of vesicular-arbuscular mycorrhiza (VAM) on the fecundity ofVulpia ciliata ssp.ambigua was investigated at two field sites in eastern England by applying the fungicide benomyl to reduce VAM infection. The application of benomyl at the two sites produced very different results. At one site the application of the fungicide reduced the fecundity of plants whereas at the other fecundity was increased. At the first site the reduction in fecundity was linked to a significant reduction in VAM infection on the sprayed plants. The mechanism of the benefit associated with the VAM infection is however unclear: there was no treatment effect on morphology or on phosphorus inflow. At the second site, where fecundity was increased, there was only a negligible amount of VAM infection amongst the unsprayed plants and it is suggested that the increase in fecundity with the application of benomyl may have resulted from a reduction in infection by other, presumably pathogenic, fungi. The value of VAM fungi to the host plant may therefore not be restricted to physiological benefits. They may also provide protection to the plant by competing for space with other species of pathogenic fungi.

Chitinase, chitosanase and β-1,3-glucanase activities in Allium and Pisum roots colonized by Glomus species

By using a two-dimensional polyacrylamide gel electrophoresis (PAGE) system, one major additional band with chitinase activity could be detected in Allium porrum (leek) root extracts after colonization by Glomus versiforme or Glomus intraradix when compared to control root extracts. After separation under native conditions in the first dimension, this band was observed both in the Davis system (designed to separate native acidic or neutral proteins) and in the Reisfeld system (designed to separate basic proteins). After the second dimension in sodium dodecyl sulfate (SDS)-PAGE under non-reducing conditions, its apparent molecular mass was determined to be about 30 kDa. In Glomus fasciculatum-colonized root extracts of Allium cepa (onion), four additional bands with chitinase activity were found. The same additional bands were obtained in onion roots colonized by the other Glomus species. Among the four bands, one of them was separated in the first dimension in both the Davis system and the Reisfeld system, two were only detected as acidic or neutral isoforms, while the last one was present as a basic isoform. Their apparent molecular masses were estimated at 33, 35 and 50 kDa. In vesicular-arbuscular mycorrhizae (VAM)-colonized pea root extracts, one acidic chitinase isoform was strongly stimulated while another acidic isoform was less highly induced in the various mycorrhizal interactions. Their apparent molecular masses were 30 and 47 kDA. Chitosanase activities were detected in leek and onion roots colonized by the different VAM fungi, while no chitosanase was observed in either non-mycorrhizal or VAM-colonized pea roots extracts. In VAM-colonized leek roots, the main chitosanase activity had an estimated apparent molecular mass of 20 kDa as determined by SDA-PAGE under non-reducing conditions. Endomycorrhizal onion roots exhibited three chitosanases with estimated apparent molecular masses of 14, 20 and 35 kDa, the two latter being induced by VAM fungal colonization. Finally, no induction of β-1,3-glucanase activity was detected in VAM-colonized roots of leek and onion. In pea roots, one β-1,3-glucanase activity was revealed, but it was not present in all VAM interactions.

Effect of fertilizer and endomycorrhizal inoculum on growth and nutrient uptake of cocoa (Theobroma cacao L.) seedlings

A greenhouse experiment was carried out to evaluate the influence of vesicular-arbuscular mycorrhiza (VAM) on growth and nutrient uptake of cocoa seedlings treated with five levels of palm oil mill effluent, in an unsterilized Oxisol and an Ultisol, either with or without addition of the VAM fungus Scutellospora calospora (Nicol. & Gred.) Walker and Sanders. Inoculation with the VAM fungi significantly increased nutrient uptake and plant growth in both soils. The dry matter yield, and the tissue N and K concentration in the plant tops increased significantly with increasing levels of palm oil mill effluent applied to both the Oxisol and the Ultisol. The maximum tissue P concentration, however, was obtained from plants grown in the Ultisol that was given 50.0 g palm oil mill effluent per kg while the maximum P recovery of 26% was obtained from plants given only 16.7 g effluent per kg. Overall, the percentage of P recovery decreased with the addition of increasing levels of palm oil mill effluent. In the Oxisol, the tissue P concentration increased with the addition of increasing levels of palm oil mill effluent, but the maximum recovery of P was recorded from plants given only 0.3 g effluent per kg. The percentage P recovery decreased with subsequent additions of the effluent.

Growth dependency of wild, primitive and modern cultivated wheat lines on vesicular-arbuscular mycorrhiza fungi

Mycorrhizal colonization and growth dependency were studied at a single rate of phosphorous application in wild and cultivated primitive and modern wheats, inoculated with Glomus intraradices Schenck & Smith. Mycorrhizal colonization found in Triticum timopheevii var. araraticum (AAGG) was higher than that found in the other tetraploid wheats (AABB). Mycorrhizal dependency was higher in representatives of the D genome donor — Aegilops squarrosa, compared with representatives of the A and possible B genome donors T. monococcum and Ae. sharonensis, Ae. longissima and Ae. speltoides, respectively. The nature of response to VAM in hexaploid wheat was controlled by factors of the A and B genomes which are epistatic over those located in the D genome. The high mycorrhizal colonization and dependency which was found in T. timopheevii var. araraticum may indicate special genomic affinity possessed by the G genome of wheat in VAM interaction. Based on the 27 wheat lines and species tested in this study only low correlation between G. intraradices colonization and its contribution to plant growth can be suggested.

Ecology of VAM fungi in tropical agrosystems

The known edaphic and climatic stress situations in the tropics imply that agronomic crops depend, for nutrition and growth, on vesicular arbuscular mycorrhizae (VAM). VAM fungal populations in tropical agrosystems may be high in quantity (concentration of infective propagules) when soils are cultivated after a fallow period, or when low levels of agronomic inputs are applied. The quality (effectiveness) of VAM populations varies among sites. Quality may be related to the composition of VAM fungal species within the native populations. Agronomic inputs to agrosystems, such as cropping practices, fertilization, weeding, pesticide applications etc. may decrease the diversity of VAM fungi and/or change the quantitative composition of fungal species due to improvement of the competitive ability of certain fungi. Possible results may also be preferential associations between certain plant and certain fungal species. The significance of differential abilities of VAM fungal species to tolerate edaphic conditions and to infect crop plants, as well as the significance of preferential associations and diversity of VAM fungi are presented. The necessity to introduce VAM fungi to disturbed tropical soils and the feasibilities to inoculate tropical agroecosystems are discussed.

Vesicular arbuscular mycorrhiza (VAM) in pioneer salt marsh plants of the Ganges river delta in West Bengal (India)

VA mycorrhizal colonization of four species of pioneer salt marsh plants including two species of chenopodiaceae at the terminal Gangetic delta in India, is reported. Five common species of VAM fungi were recorded from rhizosphere soils of the plant species. Population of spores of VAM fungi and effective inoculum potential of these fungi in rhizosphere soils as determined by the MPN-method were rather low.

VESICULAR‐ARBUSCULAR MYCORRHIZAE IN HAWAIIAN ERICALES

Vesicular‐arbuscular mycorrhizae (VAM) are reported for the first time in four species of Hawaiian Ericales, Vaccinium calycinum, V. dentatum, and V. reticulatum of the Ericaceae and Styphelia tameiameiae of the Epacridaceae. The coarse roots (> 1.5 mm diam) of many specimens were densely colonized by VAM fungi, with up to 90% of the length of roots containing arbuscules, vesicles, coils, and internal hyphae. Spores of an undescribed Glomus sp. were associated with two species of Vaccinium. The hair roots of all species bore the ericoid mycorrhizae typical of certain families of this order. The high frequency of VAM in Hawaiian populations of Ericales suggests that ancestral Ericales possessed the capacity to form both VA and ericoid mycorrhizae. An evolutionary sequence of mycorrhizal dependency in the Ericales is presented.

Mycorrhizae and rehabilitation of disturbed arid soils: Processes and practices

Abstract Vesicular‐arbuscular mycorrhizae (VAM) are critical components of arid ecosystems that regulate plant growth by improving plant nutrient and water uptake capacities. All arid plant species are capable of forming mycorrhizal associations except a limited suite of annual weeds. Almost any perturbation associated with human development serves to reduce VAM inoculum. Thus the restoration of disturbed lands depends, in part, on the restoration of viable VAM symbioses. Two means are available for restoring the symbiosis: artificial inoculation and application of succession theory. Although artificial inoculation is possible, due to the current inability to grow the endophyte, it has limited applicability. There are a wide variety of vectors of VAM fungi including animals and wind. Proper use of existing information can enhance the natural restoration of VAM symbioses. These include patch planting, planting of facultative VAM plants, and allowing animals to migrate freely across the site. These activiti...

Effects of Rhizobium and vesicular-arbuscular mycorrhiza inoculations on nodulation, symbiotic nitrogen fixation and soybean yield in subtropical-tropical fields

Field experiments were carried out to determine the effects of single and mixed inoculations with Rhizobium and vesicular-arbuscular mycorrhiza (VAM) on nodulation, symbiotic N2 fixation and yield of soybeans in six Taiwan subtropical-tropical sites. Inoculation with Rhizobium alone significantly increased nodulation, nodule weight and nitrogenase activity of nodules in three out of six experimental fields, and affected soybean yields in the range −13% to + 134%. Inoculation with VAM fungi alone did not have a significant effect on nodulation and nitrogenase activity. Mycorrhiza inoculation affected soybean yields in the range −13% to + 65%, but only the yield increases at one out of six sites with N application were statistically significant. Mixed inoculation with Rhizobium and mycorrhiza affected yields in the range −8% to + 145% A synergistic effect from mixed inoculation of Rhizobium-mycorrhiza on soybean yields was found in one out of six experimental fields. The yield response to N application (40 kg N ha−1) in these six paddy-field trials was not significant. These results suggest that single or mixed inoculation of rhizobia can greatly assist soybean grain yields and can replace N fertilizers.

Effects of VA mycorrhiza on yield and harvest index of field-grown pea

A field experiment was carried out to study the influence of vesicular-arbuscular mycorrhiza (VAM) on nutrient uptake and growth of pea at two levels of P fertilizer. Pea was grown in dazomet-fumigated and non-fumigated soil, either with or without addition of inoculum of VAM fungi. Dazomet efficiently eliminated infection by indigenous VAM fungi, whereas roots from untreated soil were extensively infected. Inoculation with VAM fungi increased P uptake by peas in fumigated plots, but had no significant effect on dry matter production in either soil treatment. However, VAM developed less in inoculated fumigated than in untreated plots. Seeds of uninfected plants in fumigated plots contained only 56 and 81%, respectively, of the P and dry matter content of seeds of infected plants in untreated plots. The addition of 60 kg P ha−1 also increased seed yields but to a smaller degree than VAM. The seed yield as a proportion of total shoot yield (harvest index) was higher in VAM infected than in uninfected peas but was unaffected by P fertilizer. The possible reasons for this are discussed.