Interaction of Vesicular-Arbuscular Mycorrhizae and Cultivars of Alfalfa Susceptible and Resistant to Meloidogyne hapla

The interaction between vesicular-arbuscular mycorrhizal (VAM) fungi and the root-knot nematode (Meloidogyne hapla) was investigated using both nematode-susceptible (Grasslands Wairau) and nematode-resistant (Nevada Synthetic XX) cultivars of alfalfa (Medicago sativa) at four levels of applied phosphate. Mycorrhizal inoculation improved plant growth and reduced nematode numbers and adult development in roots in dually infected cultures of the susceptible cultivar. The tolerance of plants to nematode infection and development when preinfected with mycorrhizal fungi was no greater than when they were inoculated with nematodes and mycorrhizal fungi simultaneously. Growth of plants of the resistant cultivar was unaffected by nematode inoculation but was improved by mycorrhizal inoculation. Numbers of nematode juveniles were lower in the roots of the resistant than of the susceptible cultivar and were further reduced by mycorrhizal inoculation, although no adult nematodes developed in any resistant cultivar treatment. Inoculation of alfalfa with VAM fungi increased the tolerance and resistance of a cultivar susceptible to M. hapla and improved the resistance of a resistant cultivar.     

Effects of rhizosphere soil,vesicular-arbuscular mycorrhizal fungi and phosphate onPlantago major L. ssp.pleiosperma Pilger

Biotic factors in the rhizosphere and their effect on the growth ofPlantago major L. ssp.pleiosperma Pilger (Great plantain) were studied. In a pot experiment the effect on shoot growth of the addition of 2.5% rhizosphere soil at four levels of phosphate was highly dependent on the availability of phosphate: a promoting effect at low phosphate levels was observed while a reducing effect occurred at higher phosphate levels. As the roots were infected with vesicular-arbuscular mycorrhizal (VAM) fungi in the treatment with rhizosphere soil, two other experiments were set up to separate effects of the indigenous VAM fungi from effects of the total rhizosphere population. The uptake of phosphate and shoot growth was not decreased at higher phosphate availability when VAM inoculum was added alone or in combination with rhizosphere soil. The growth reducing effect of the rhizosphere soil could therefore not be ascribed only to mycorrhizal infection. The results suggest that biotic factors in the rhizosphere soil affect the phosphate uptake ofPlantago major ssp.pleiosperma. This may, under conditions of phosphate limitation, lead to an increase of phosphate stress and, subsequently, a growth reduction. Futhermore, it is concluded that VAM fungi, as part of the rhizosphere population, may compensate this phosphate stress by enhancing the phosphate uptake.Grassland Species Research Group Publication No. 148.     

Potentials and limitations of mycorrhizal inoculation illustrated by experiments with field-grown cassava

Summary Field inoculation trials with cassava (Manihot esculenta Crantz) were conducted in Quilichao (typic Dystropept soil) and Carimagua (Haplustox soil). In Quilichao, with a large and effective native VA-mycorrhizal (VAM) population, inoculation withGlomus manihotis did not increase cassava yields significantly, neither when different sources and levels of inoculum material were used, nor with different cassava cultivars, or after stabilizing soil temperature through mulching. Field inoculation did result in a decrease of the coefficient of variation with respect to yield. The high dependency of cassava on an effective VAM association was indicated by a marked decrease in yield after eradication of native VAM by soil sterilization. In Carimagua, with a lower native VAM population, mycorrhizal inoculation withG. manihotis increased yields significantly at intermediate levels of 100 kg/ha of applied P, using either inoculum of cassava orPanicum maximum roots or inoculum of a soil-root mixture of maize or tropical kudzu. Higher or lower levels of P decreased the effect of inoculation on yield. There were no significant differences among P sources, ranging from highly soluble triple superphosphate to low solubility rock phosphates. Inoculation with different VAM isolates had a variable effect on cassava yields, and showed that there may be an interaction between P fertilizer level and isolate efficiency. It is concluded that there may be a potential to increase yields or decrease the fertilizer P requirements of cassava through field inoculation with effective VAM isolates, in the vast areas of acid infertile Oxisols and Ultisols with low native VAM fungal populations, represented by Carimagua.     

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.     

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 mycorrhizal inoculation and soluble phosphorus fertilizer on growth and phosphorus uptake of pearl millet

Summary Six mycorrhizal fungi were tested as inoculants for pearl millet (Pennisetum americanum Leeke) grown in pots maintained in a greenhouse. VAM fungi varied in their ability to stimulate plant growth and phosphorus uptake. Inoculation withGigaspora margarita, G. calospora andGlomus fasciculatum increased shoot drymatter 1.3 fold over uninoculated control. In another pot trial, inoculation withGigaspora calospora andGlomus fasciculatum resulted in dry matter and phosphorus uptake equivalent to that produced by adding phosphorus at 8 kg/ha.The influence of inoculatingGigaspora calospora on pearl millet at different levels of phosphorus fertilizer (0 to 60 kg P/ha) as triple superphosphate in sterile and unsterile alfisol soil was also studied. In sterile soil, mycorrhizal inoculation increased dry matter and phosphorus uptake at levels less than 20 kg/ha. At higher P levels the mycorrhizal effect was decreased. These studies performed in sterilized soil suggest that inoculation of pearl millet with efficient VAM fungi could be extremely useful in P deficient soils. However, its practical utility depends on screening and isolation of fungal strains which perform efficiently in natural (unsterilized) field conditions.     

Effects on plant growth of inoculation of stored stripmining topsoil in North Dakota with mycorrhizal fungi contained in native soils

Stored topsoil from stripmining operations in western North Dakota was inoculated with mycorrhizal fungi contained in native prairie soil. The effects on plant mycorrhizal infection percentage, growth as shoot dry weight, and phosphorus uptake were determined. The studied topsoil piles were found to contain little or no vesicular arbuscular mycorrhizal (VAM) fungal inoculum at a depth of 120 cm. The inoculum soil was mixed into the stored soil at rates of 10% and 1%, or surface-applied at 1%. In control pots, sterilized inoculum soil was used. Corn plant (Zea mays) bioassays were used. After 30 days growth the percent VAM fungal infection of the test plants increased with both the 10% and 1% soil inocula. Phosphorus concentrations were generally increased by inoculation with 10% soil mixtures but not 1%. Shoot dry weights of the plants were not measurably different between 10% and 1% inoculation. However, when the plant growth period was increased to 60 days, all three parameters were increased over the check plants. When the inoculum was not mixed into the soil, but layered on the surface, there were no differences in any of the parameters.     

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.     

Field nursery inoculation of Hevea brasiliensis Muell. Arg. seedling rootstock with vesicular-arbuscular mycorrhizal (VAM) fungi

The growth response of Hevea brasiliensis to vesicular-arbuscular mycorrhizal (VAM) fungi inoculation was assessed in two field nursery sites containing indigenous mycorrhizal fungi (IMF). Seedling rootstocks were inoculated with mixed VAM-fungal species in a factorial combination with phosphorus (P) fertilizer application, and planted in randomised blocks on sandy (site 1) and clayey (site 2) soils. Plants were harvested after 26 weeks for measurements of shoot dry weight (DW), stem diameter, height, mycorrhizal root colonization and leaf nutrient contents. At site 1, VAM increased shoot DW, stem diameter and plant height only in treatments without P applied. Increases in shoot DW due to VAM were 70% greater than the uninoculated controls although this was reduced to 5% when P was applied. At site 2, VAM inoculation also increased shoot DW and stem diameter but the magnitude of the increases was smaller. Shoot DW response due to VAM was only 29%. At this second site, applying phosphate to uninoculated plants did not increase shoot yields further. Leaf concentrations of all nutrients were unaffected by VAM at both sites, except for copper (Cu) which was increased by VAM in treatments where P was not applied. However, leaf contents of P, potassium (K), magnesium (Mg) and Cu were increased by VAM at site 1, and of leaf nitrogen (N) and K at site 2. These experiments demonstrate that VAM-fungi could be introduced into field nursery sites to improve growth and P uptake by H. brasiliensis. The relevance of VAM-fungi to H. brasiliensis seedling rootstock development and the influence of IMF in determining field responses is discussed.     

Interaction of vesicular-arbuscular mycorrhizal fungi and root knot nematode on cultivars of tomato and white clover susceptible to Meloidogyne hapla

The interactive effects of vesicular-arbuscular mycorrhizal (VAM) fungi and root-knot nematode (Meloidogyne hapla) were studied on nematode-susceptible cultivars of tomato (cv. Scoresby) and white clover (cv. Huia) at four levels of applied phosphate. The relative merits of simultaneous inoculation with mycorrhizal fungi and nematodes and of inoculation with mycorrhizal fungi prior to nematode inoculation were evaluated. Mycorrhizal plants were more resistant than non-mycorrhizal plants to root-knot nematode at all phosphate levels and growth benefits were generally greater in plants preinfected with mycorrhizal fungi. Nematode numbers increased with increasing levels of applied phosphate. In mycorrhizal root systems, nematode numbers increased in the lower phosphate soils; at higher phosphate levels nematode numbers were either unaffected or reduced. The numbers of juveniles and adults per gram of root were always lower in mycorrhizal treatments. Mycorrhizal root length remained unaffected by nematode inoculation. Mycorrhizal inoculation thus increased the plants' resistance to infection by M. hapla. This was probably due to some alteration in the physiology of the root system but was not entirely a result of better host nutrition and improved phosphorus uptake by mycorrhizal plants.     

Response ofLeucaena leucocephala to vesicular-arbuscular mycorrhizal colonization and rock phosphate fertilization in an Oxisol

Response ofLeucaena leucocephala (Lam) de Wit to rock phosphate application and inoculation with the vesicular-arbuscular mycorrhizal (VAM) fungusGlomus aggregatum (Schenck and Smith emend Koske) was evaluated in a pot experiment. VAM colonization increased as rock phosphate application increased. Using phosphorus concentration in pinnules as an indicator of VAM activity, significant VAM activity occurred at 25 days after planting at the lower levels of rock phosphate application (0, 0.34 and 0.68 g P kg^–1). The time required for significant VAM activity was shortened by 5 days at the higher P levels (1.36, 2.72 and 5.44 g P kg^–1). The highest VAM activity was associated with the highest rate of rock phosphate application.Inoculation withG. aggregatum significantly increased the uptake of Cu, P and Zn and dry-matter yield at all levels of rock phosphate applied. Copper concentrations in roots of mycorrhizal Leucaena were significantly higher than that of shoots. The results indicated that Leucaena in symbiotic association with VAM fungi effectively utilized P from rock phosphate. However, high rates of rock phosphate are required to attain growth comparable to that obtained with the application of water-soluble phosphate.Contribution from Hawaii Institute of Tropical Agriculture and Human Resources, Journal Series No. 3243.     

Interactions between vesicular-arbuscular mycorrhizal fungi and asparagus

Summary The vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus versiforme increased significantly the growth ofAsparagus officinalis under controlled conditions using Turface as the growth medium. The growth responses, including increases in root fresh weight, numbers of shoots, shoot dry weight, and shoot height follow a pattern similar to other mycorrhizal systems. Indigenous VAM fungi appeared to have negative effects on average shoot fresh and dry weight, number of shoots per pot and average shoot height on one year oldA. officinalis seedlings obtained from the field and grown under controlled conditions. These results may be due either to the high levels of soluble phosphate present in the soil or the ineffectiveness of the particular indigenous fungi as mycorrhizal fungi in asparagus. Indigenous mycorrhizal fungi overwinter in asparagus root crown as vesicles and as external and internal hyphae. Soil obtained from the same fields as the one year old crowns was a good source of mycorrhizal inoculum for sterile seedlings.     

The effect of VA mycorrhizal fungi,phosphorus and drought stress on the growth of Acacia nilotica and Leucaena leucocephala seedlings

The effect of vesicular-arbuscular mycorrhizal (VAM) fungi on growth and drought resistance of Acacia nilotica and Leucaena leucocephala seedlings was studied in a glasshouse experiment. The experimental design was a 2·2·2 factorial: ± mycorrhizal inoculation, ± application of phosphorus fertilizer and ± repeated drought treatment. The growth promoting effect of VAM fungi equalled the effect of phosphorus fertilization after 12 weeks. The drought treatment reduced seedling biomass and nodulation. Differences between the plant species were found with respect to growth improvements due to VAM inoculation and/or phosphorus fertilization under drought stress conditions. The results are discussed in relation to plant drought resistance and reforestation in the subhumid to arid tropics.     

Axenic culture and encapsulation of the intraradical forms of Glomus spp.

In recent years there have been many attempts to cultivate in vitro vesicular-arbuscular mycorrhizal (VAM) fungi which are obligate symbionts. Resting spores extracted from soils are often used as inoculum. Mycorrhizal root pieces are also used for inoculation but the role of intra-radical structures has not been clearly established. On agar medium vegetative mycelium was regenerated from individual intra-radical vesicles and from hyphae extracted by enzymatic maceration. After cell penetration, the mycelium probably accumulates substances which allow growth of VAM fungi in pure culture. When associated with tomato roots, this mycelium forms typical mycorrhizae. Encapsulation stabilized the biological properties of mycorrhizal roots and isolated vesicles. The immobilization also preserved the infectivity of the intra-radical hyphae and vesicles. After 25 years of exclusive utilization of resting spores as starting material for axenic and dual cultures of VAM fungi, it appears that intra-radical vesicles may be preferable propagules.D.-G. Strullu and C. Romand are with the Université d'Angers, Laboratoire de Phytonique, 2 Boulevard Lavoisier, 49045 Angers Cedex, France. C. Plenchette is with INRA, Station d'Agronomie, 17 rue Sully, 21034 Dijon Cedex, France.     

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.     

Indigenous and introduced arbuscular mycorrhizal fungi contribute to plant growth in two agricultural soils from south-western Australia

Arbuscular mycorrhizal (AM) fungi occur in all agricultural soils but it is not easy to assess the contribution they make to plant growth under field conditions. Several approaches have been used to investigate this, including the comparison of plant growth in the presence or absence of naturally occurring AM fungi following soil fumigation or application of fungicides. However, treatments such as these may change soil characteristics other than factors directly involving AM fungi and lead to difficulties in identifying the reason for changes in plant growth. In a glasshouse experiment, we assessed the contribution of indigenous AM fungi to growth of subterranean clover in undisturbed cores of soil from two agricultural field sites (a cropped agricultural field at South Carrabin and a low input pasture at Westdale). We used the approach of estimating the benefit of AM fungi by comparing the curvature coefficients ( C) of the Mitscherlich equation for subterranean clover grown in untreated field soil, in field soil into which inoculum of Glomus invermaium was added and in soil fumigated with methyl bromide. It was only possible to estimate the benefit of mycorrhizas using this approach for one soil (Westdale) because it was the only soil for which a Mitscherlich response to the application of a range of P levels was obtained. The mycorrhizal benefit ( C of mycorrhizal vs. non-mycorrhizal plants or C of inoculated vs. uninoculated plants) of the indigenous fungi corresponded with a requirement for phosphate by plants that were colonised by AM fungi already present in the soil equivalent to half that required by non-mycorrhizal plants. This benefit was independent of the plant-available P in the soil. There was no additional benefit of inoculation on plant growth other than that due to increased P uptake. Indigenous AM fungi were present in both soils and colonised a high proportion of roots in both soils. There was a higher diversity of morphotypes of mycorrhizal fungi in roots of plants grown in the Westdale soil than in the South Carrabin soil that had a history of high phosphate fertilizer use in the field. Inoculation with G. invermaium did not increase the level of colonisation of roots by mycorrhizal fungi in either soil, but it replaced approximately 20% of the root length colonised by the indigenous fungi in Westdale soil at all levels of applied P. The proportion of colonised root length replaced by G. invermaium in South Carrabin soil varied with the level of application of P to the soil; it was higher at intermediate levels of recently added soil P.     

Soil color and surface residue effects on seedling light environment

Three leafless pea cultivars (JI 1198, BS 142 and BS 4) with the same phenotype and similar patterns of development, were tested in a sterilized low-phosphate soil for their response to phosphate fertilizer and to vesicular-arbuscular mycorrhizal (VAM) infection by threeGlomus species. Cultivar JI 1198 was very responsive to phosphate but not to inoculation withGlomus mosseae, Glomus caledonium orGlomus epigaeum. Phosphate and VAM treatments increased growth of cultivar BS 142 but were ineffective with cultivar BS 4. Fungal infectivity could not be related with endophyte effectiveness at stimulating plant growth, although the percentage of root length infected by each one of the threeGlomus species did not vary between cultivars. Genetic differences among plant cultivars can thus markedly affect the symbiosis between the host root and VAM fungi; this suggests that potential host-endophyte combinations need to be evaluated before being tested in the field.     

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.     

Effect of vesicular-arbuscular mycorrhizal fungi and ofagrobacterium radiobacter on maize growth

An influence of dual inoculation with the rhizosphere bacteriumAgrobacterium radiobacter, and the VAM fungi,Glomus mosseae andGlomus sp., on maize growth and mycorrhizal infection was observed. Separate inoculations of bacteria or fungi showed significant positive effects on the shoot biomass production of pot-cultured plants only at the last of three consecutive harvests. Plant biomass production was enhanced substantially after a dual inoculation with bacteria and fungi. Synergistic interaction of fungal and bacterial inoculation and growth stimulation was evident at all three harvests compared to uninoculated plants and also compared to plants inoculated with fungi or bacteria only. The dual inoculation increased the shoot biomass of plants by approximately 30% as compared with control. No significant differences were found in mycorrhizal infection between plants uninoculated and inoculated with bacteria.Agrobacterium radiobacter seems to be compatible with mycorrhizal symbiosis and can act a synergistic partner of some VAM fungi.     

The management of populations of vesicular-arbuscular mycorrhizal fungi in acid-infertile soils of a savanna ecosystem

A field trial was conducted at two sites in the savanna ecosystem of eastern Colombia to compare the effects of inoculation with vesicular-arbuscular mycorrhizal fungi (VAMF) ofBrachiaria dictyoneura (a tropical grass), cassava (Manihot esculenta), the tropical forage legume kudzu (Pueraria phaseoloides) andSorghum sp., and two phosphate sources. The second stage of the trial studied the effect of these pre-crop treatments on the subsequent growth, nutrition and VAM status of cowpea (Vigna unguiculata) andStylosanthes capitata in the following season, compared with both crops sown in native savanna. Inoculation significantly increased the levels of VAM and plant yields in the early growth stages of all crops during the first season, particularly with the rock phosphate (RP) source. The most significant increases were observed in the mycorrhiza-dependent cassava and kudzu crops up to 15 weeks after sowing, and were associated with increased foliar uptake of P and Mg. The effectiveness of the introduced inoculum was greater at the field site with a sandier soil. In the second season the levels of VAM in roots of cowpea andS. capitata were all increased significantly in pre-cropped plots compared with a savanna control. The increased presence of VAM was associated with significantly increased yields on plots previously sown to cassava, kudzu andSorghum sp. The data support the idea that increasing the VAMF inoculum potential of these acid-infertile soils by inoculation or pre-crops can greatly increase the rate of establishment of mycorrhiza-dependent host plants.