Enhancement of nitrogen fixation in lentil,faba bean,and soybean by dual inoculation with Rhizobia and mycorrhizae

The combined effect of Vesicular Arbuscular Mycorrhizae (VAM) and Rhizobium on the cold season legumes, lentil and faba bean, as well as on summer legume, soybean, were studied in soils with low indeginous VA mycorrhizal spores. Inoculation of the plant with VA mycorrhizal fungi increased the level of mycorrhizal root infection of lentil, faba bean and soybean. The inoculation with Rhizobium had no significant effect on VA mycorrhizal infection percent, but VA mycorrhizal inoculation increased nodulation of the three legumes. The inoculation with Rhizobium alone significantly increased plant dry weight and N content of lentil and faba bean as well as seed yield of soybean. VA mycorrhizal inoculation also significantly increased plant dry weight and phosphorus content of the plants as did fertilization with superphosphate. Rock phosphate fertilization, however, had no significant effect on plant growth or phosphorus uptake. The addition of rock phosphate in combination with VA mycorrhizal inoculation significantly increased plant dry weight and P uptake of the plants. The dual inoculation with both rhizobia and mycorrhizae induced more significant increases in plant dry weight, N and P content of lentil and faba bean as well as seed yield of soybean than inoculation with either VA mycorrhizae or Rhizobium alone.     

Effect of root exudation on VA mycorrhizal infection at early stages of plant growth

Summary No relationship between the degree of VA mycorrhizal infection and total sugar content in root exudates of several plant species of different degree of mycorrhizal susceptibility were observed during the early stages of plant growth. Even more, the non host plants tested showed higher sugar exudation ability, when expressed as the amount exuded per g of root, at these early periods of their growth, than plants susceptible to mycorrhizal infection.Root exudates from host and non host plants influenced similarly the percentage of spore germination and number of secondary spores under controlled conditions.     

Effect of VA Mycorrhizal Inoculation on Growth of Asparagus Seedlings

Experiments on asparagus (Asparagus of)icinalis L.) inoculated with VA mycorrhizal fungi were conducted under two fluvo-aquatic phosphorus deficient soils. This study was to examine the growth response of VA mycorrhizae and fertilizer effects on the growth of mycorrhizal and non-mycorrhizal asparagus seedlings in pots and under field conditions. Inoculation with VA mycorrhizal fungi significantly increased mycorrhizal infection and enhanced seedling growth. In treatments of fertilization by different batches of NPK or by different amount of application it was shown that phosphorus was most favourable to VAM activity. Both the prevalance of mycorrhizal infection and the dry weight of seedlings in treatment with NPK in 1:0:1 was similar to that in 1:1:1 and 1:2:1 after inoculation. Further more the prevalance of infection, plant growth and P content in the treatment of 1/2 an amount of NPK in 1:1:1 were even higer than those in full amount of NPK and in non-fertilization. It is indicated that phosphorus uptake and plant growth benefit greatly by mycorrhizal inoculation. Mycorrhizal plant requires only about half as much phosphorus to achieve maximum growth as the uninoculated plants.     

Effect of cyanazine herbicide on VA mycorrhizal infection and growth ofPisum sativum

The effect of the photosynthetic inhibitor herbicide Cyanazine on VA mycorrhiza and on pea plant growth was examined. Plant growth was decreased by Cyanazine applied at the rate of 0.05 and 0.1 mg ml⁻¹. Cyanazine only decreased VA mycorrhiza of pea roots when applied at high doses (0.1 mg ml⁻¹). However, no direct effect of the herbicide on VA endophyte development was found. These results suggest that the inhibitory effect of Cyanazine on VA mycorrhiza took place via influence on plant metabolism and growth. VA mycorrhizas alleviated the deleterious effect of the herbicide on plant growth when applied at moderate (0.05 mg ml⁻¹) but not at high (0.1 mg ml⁻¹) doses.     

The effects of fungicide-coated seeds on the establishment of VA mycorrhizal infection

Commercial fungicide-coated seed of five plant species was tested to determine whether the fungicides used affected seedling infection by VA mycorrhizal fungi. All the plants became mycorrhizal, with no differences between those emerging from fungicide-coated or non-fungicide-coated seed. However, when the same fungicides were applied as soil drenches, mycorrhizal infection was greatly inhibited, and in some instances was absent throughout the duration of the experiment.     

Effect of soil volume and plant density on mycorrhizal infection and growth response

Summary The effect of soil volume and plant density on mycorrhizal infection and growth response was studied with onion. There was a significant negative correlation between percentage vesicular-arbuscular mycorrhizal infection and root density. The growth response due to mycorrhiza decreased when less soil was available for the plant. The root: shoot ratio decreased with increasing plant density in both mycorrhizal and non-mycorrhizal plants. Pot size did not affect the root: shoot ratio.     

Effect of vesicular arbuscular mycorrhiza and soluble phosphate onAbelmoscus esculentus (L.) Moench

Summary Effect of VA mycorrhiza and soluble phosphorus onAbelmoscus esculentus (L.) Moench was studied in a phosphorus deficient sandy loam soil with pH 5.5. The mycorrhizal infection and spore production were reduced by an increase of added soluble phosphorus. Root, shoot and total plant dry weight were significantly greater in mycorrhizal plants than in non-mycorrhizal controls, at all levels of added soluble P. Mycorrhizal dependency was found to decrease with increase in added soluble P. Depression of growth, as compared with growth at 100% was noticed in mycorrhizal plants when 200% of the recommended P was added.     

Effect of fungicides on mycorrhizal colonization and growth of onion

Summary Effect of five fungicidesviz Agrosan. Benlate, Captan, Ceresan and Plantavax on VA mycorrhizal symbiosis in onion was studied in a phosphorus deficient, sandy loam soil. Two levels of fungicides (2.5 g and 25 g/g soil) were applied to the soil. Agrosan, Benlate and Plantavax applied at 25 g/g soil reduced the mycorrhizal colonization significantly. All the fungicides, except Captan, applied at lower concentration reduced plant growth and P uptake. Captan applied at the lower concentration had no effect on mycorrhizal colonization, plant growth and P uptake, and when applied at higher concentration had least effect on plant growth compared to other fungicides.Contribution of U.A.S. Research project DR/AMB-1.     

Acacias respond to additions of phosphorus and to inoculation with VA mycorrhizal fungi in soils stockpiled during mineral sand mining

Three pot experiments were conducted to test the hypothesis that the growth ofAcacia spp. in stockpiled soil from two mineral sand mines, could be increased by the addition of phosphorus (P) or inoculation with VA mycorrhizal fungi. In soils from North Stradbroke Island, the dry weight of shoots ofAcacia concurrens was increased by P and by VA mycorrhizal fungi in tailings sand, while in less adsorptive topsoil dry weight was only increased at low levels of applied P. WhenA. concurrens was grown in a layer of topsoil placed over tailings sand, shoot dry weight increased, in response to inoculation with VA mycorrhizal fungi banded between the soil layers.In topsoil from Eneabba, the dry weight of shoots at low rates of applied P was increased by up to 4 times by inoculation with VA mycorrhizal fungi. The response to inoculation in both experiments was due to increases in the uptake of P by the plants.Species of VA mycorrhizal fungi differed in their ability to increase plant growth. However, in soils from both sites, the same fungal species were effective.     

VA菌根真菌与植物相互选择性的研究

采用土培试验了灭菌条件下同一菌种对不同植物和不同菌咱对同一植物的接种效应。试验结果表明,供试植物都能与ＶＡ菌根真菌形成共生体系,接种ＶＡ菌根真菌促进了植物的生长,植株干物质量显著是否 同ＶＡ菌根真菌与宿主植物形成共生体的能力及对植物的接种疚差异明显,由此可见,选择优势菌咱和宿主植物组合,对于ＶＡ菌根真菌的广泛应用及农业生产具有重要的实践作用。     

Relationship between the concentration of sugars in the roots and VA mycorrhizal infection

Summary The VA-infected wheat varieties showed an increase of total (Lozano var.) and reducing (Lozano and Pane vars.) sugars in their root extracts. However, no clear relationship between sugar concentration in the root and VA mycorrhizal infection level could be established.In addition, the VA mycorrhizal hosts sorghum, alfalfa, sunflower and maize, and non-host radish and cabbage plants were tested for sugar content in their root extracts after fifteen days of growth. Sugars present in the root extracts of these plants did not seem to be a decisive factor in plant susceptibility to VA infection.     

Mycorrhizal symbiosis increases growth,reproduction and recruitment of Abutilon theophrasti Medic. in the field

We examined in the field the effect of the vesicular-arbuscular (VA) mycorhizal symbiosis on the reproductive success of Abutilon theophrasti Medic., an early successional annual member of the Malvaceae. Mycorrhizal infection greatly enhanced vegetative growth, and flower, fruit and seed production, resulting in significantly greater recruitment the following year. In addition, the seeds produced by mycorrhizal plants were significantly larger and contained significantly more phosphorus than seeds from non-mycorrhizal plants, an effect which may improve offspring vigor. Infection by mycorrhizal fungi may thus contribute to the overall fitness of a host plant and strongly influence long-term plant population dynamics.     

Controls for rhizosphere microorganisms to study effects of vesicular-arbuscular mycorrhizae on Artemisia tridentata

Seven treatments were set up to test the effects of vesicular-arbuscular (VA) mycorrhizal fungi and other rhizosphere microorganisms on the growth of Artemisia tridentata ssp. tridentata. Soil sievings had no significant effect on root or shoot mass. Spores and surface-sterile spores were a poor inoculum source, but roots and fresh soil caused 45–75% mycorrhizal infection. Whereas root-inoculated plants still had low growth responses by the end of the experiment, fresh soil inoculum caused the greatest response, and partial fresh inoculum caused a lesser response. These results suggest that fresh soil is an appropriate inoculum for this plant-fungal-soil system, and that the major effect on plant growth of the fresh soil inoculum is from the mycorrhizal fungi and not from the other microorganisms, because the sievings had no effect on plant growth. In addition, soil dilution plating of saprophytic fungi showed 85% species similarity between sterile and fresh soil inoculum by the end of the experiment. Since the effects of non-VA microorganisms are complex and varied, we suggest that researchers work out the type of mycorrhizal controls that best suit their system.     

Differential plant response to inoculation with two VA mycorrhizal fungi isolated from a low-pH soil

Sericea lespedaza and ladino clover were inoculated withAcaulospora laevis andGigaspora margarita VA mycorrhizal fungi, both isolated from a local soil having a pH of 4.4. Plants were grown in a greenhouse in fumigated (methyl bromide) soil with four rates of applied P. This soil had a pH of 5.1 for theG. margarita experiment and a 5.8 for theA. laevis experiment. Neither plant species responded to theG. margarita isolate in terms of mycorrhizal infection of roots, top growth, or elemental uptake. TheA. laevis isolate caused increased growth of Ladino clover at the lowest rate of P application and increased growth of sericea lespedeza at the two lowest P application rates. Shoot tissue concentrations of P for both plant species were greater at the two lowest rates of P application when inoculated withA. laevis. Inoculation withA. laevis also resulted in different VAM fungal root colonization patterns between the two plant species as a function of P application rate. Roots of both plants had high infection rates (near 70%) for the two lowest P application rates but sericea lespedeza declined to 40 and 6% at the next two P application rates, respectively, whereas infection in Ladino clover was 74 and 41% at the next two P application rates, respectively. The results of this study support the concept that plant host-VAM fungal endophyte interactions are extremely variable and that characterization of individual combinations must be done if types and magnitudes of responses are to be defined.     

Vesicular-arbuscular mycorrhizas and soil salinity

This review discusses the growth and activity of vesicular-arbuscular (VA) mycorrhizal fungi in saline conditions. The review includes examination of the effects of high concentrations of salts on the occurrence of VA mycorrhizal fungi in field soils, and on spore germination, growth of hyphae, establishment of the symbiosis and production of spores in controlled conditions. Information on the growth and reproduction of VA mycorrhizal fungi under saline conditions is scarce and is often circumstantial. There is clear evidence that germination of spores and subsequent hyphal growth of some VA mycorrhizal fungi are reduced by increasing concentration of salts. However, in plant growth experiments, experimental designs and methodologies have generally not allowed the direct effects of salinity on fungal growth to be separated from plant-mediated effects. There is a need for controlled studies to investigate the responses of VA mycorrhizal fungi to soil salinity. Research is required which distinguishes between effects on different phases of the fungus lifecycle and which includes in its design the ability to separate direct effects from plant-mediated influences on fungal growth and reproduction.     

The role of the external mycelial network of vesicular-arbuscular mycorrhizal fungi: a study of carbon transfer between plants interconnected by a common mycelium

The transfer of ¹⁴C from Lolium perenne (the donor) to Plantago lanceolata (the receiver), mediated by vesicular-arbuscular (VA) mycorrhizal fungi, was examined when the two species were grown together or separately. The VA mycorrhizal infection led to a significant increase, relative to that in uninfected plants, in the ¹⁴C transferred from donor to receiver plants, not only when the roots of the two plants were growing in intimate mixture, but also when they were separated by a root-free zone of 2.33 cm. The majority of isotope transfer between the two plant species was along the direct pathway via VA mycelium.     

Effects of belowground grazing by collembola on growth,mycorrhizal infection,and P uptake of Geranium robertianum

We hypothesized that the grazing of vesicular-arbuscular mycorrhizal (VAM) hyphae by soil animals could be responsible for the lack of a direct relationship between mycorrhizal infection intensity and nutrient uptake under field conditions. To test this hypothesis, we determined the effect of a range of densities of the collembola, Folsomia candida, on growth, VAM infection, and P uptake in Geranium robertianum, a common forest herb, under greenhouse conditions. Total and aboveground growth were greater at low collembola density than either at higher collembola density or without collembola. These differences were greater when the plants were grown in a high organic content soil mix than when grown in sand. Root mass was not affected by collembola density. In the soil mix, root length decreased with increasing collembola density, but not in the sand. The percent of root length infected with VAM was lower at any collembola density than when collembola were absent. Total infected root length decreased linearly with increasing collembola density. Few significant differences in P uptake or tissue concentration were found. Thus, plant growth (but not P uptake) may be stimulated at low collembola density and inhibited at high. We discuss mechanisms which may be responsible for this non-linear response, and the implications of the pattern of response to studies of plant competition, nutrient turnover, and revegetation.     

Density dependent interactions between VA mycorrhizal fungi and even-aged seedlings of two perennial Fabaceae species

Summary The interaction of density and mycorrhizal effects on the growth, mineral nutrition and size distribution of seedlings of two perennial members of the Fabaceae was investigated in pot culture. Seedlings of Otholobium hirtum and Aspalathus linearis were grown at densities of 1, 4, 8 and 16 plants per 13-cm pot with or without vesicular-arbuscular (VA) mycorrhizal inoculum for 120 days. Plant mass, relative growth rates, height and leaf number all decreased with increasing plant density. This was ascribed to the decreasing availability of phosphorus per plant as density increased. O. hirtum was highly dependent on mycorrhizas for P uptake but both mycorrhizal and non-mycorrhizal A. linearis seedlings were able to extract soil P with equal ease. Plant size distribution as measured by the coefficient of variation (CV) of shoot mass was greater at higher densities. CVs of mycorrhizal O. hirtum plants were higher than those of non-mycorrhizal plants. CVs of the facultatively mycorrhizal A. linearis were similar for both mycorrhizal and non-mycorrhizal plants. Higher CVs are attributed to resource preemption by larger individuals. Individuals in populations with high CVs will probably survive stress which would result in the extinction of populations with low CVs. Mass of mycorrhizal plants of both species decreased more rapidly with increasing density than did non-mycorrhizal plant mass. It is concluded that the cost of being mycorrhizal increases as plant density increases, while the benefit decreases. The results suggest that mycorrhizas will influence density-dependent population processes of faculative and obligate mycorrhizal species.     

Jasmonic acid affects mycorrhization of spruce seedlings with Laccaria laccata

 Jasmonic acid (JA) was shown to be an important regulating molecule after wounding and pathogen attack, but it also conveys mycorrhizal signalling. It was therefore applied to the ectomycorrhizal system. Root growth patterns of 2-month-old spruce seedlings mycorrhized with Laccaria laccata after treatment with 0.5 μM JA, 5.0 μM JA, or none for the control, were studied using a paper-sandwich technique. Changes in plant weight, root length, the degree of branching, presence of root hairs, and infection parameters were monitored for 26 days. Data were analysed by means of Student’s t-test and ANOVA factorial. Shoot and root dry weights were significantly increased by mycorrhizal infection, especially when JA was applied. Lateral root formation and the presence of roots with hairs were dramatically decreased in the presence of the fungus. A synergistic effect of JA and mycorrhization on decrease of lateral root length was shown. The first mycorrhizal contact of fungal hyphae with roots was significantly accelerated after treatment with JA. Received: 18 December 1996 / Accepted: 26 May 1997     

The fungicides Terrazole and Terraclor and the nematicide Fenamiphos have little effect on root colonisation by Glomus mosseae and growth of cotton seedlings

 The effect of three pesticides on the initiation and early development of arbuscular mycorrhiza in cotton was examined in experiments under controlled conditions. The fungicides Terrazole and Terraclor initially inhibited mycorrhizal infection of roots of cotton. The inhibition disappeared after 4 weeks, and neither fungicide had a lasting effect. The nematicide Fenamiphos slightly increased shoot dry weight at 6–10 weeks from planting and had no effect on mycorrhizal infection. We conclude that these pesticides have no sustained, detrimental effect on mycorrhizal infection or growth of cotton seedlings when applied at recommended rates. Accepted: 30 May 1997