Arbuscular Mycorrhizal Fungi Propagules Research Articles

Glomales species associated with surface and deep rhizosphere of Faidherbia albida in Senegal

Five arbuscular mycorrhizal (AM) fungal species were isolated and propagated from surface and deep rhizospheres of Faidherbia albida trees growing in two ecoclimatic zones of West Africa: the semi-arid Sahelian and the more humid Sudano-Guinean areas. Of these species, Glomus aggregatum, Glomus caledonium, and Glomus mosseae were trapped by F. albida roots when cultivated with either surface or deep soils. Glomus fasciculatum was found exclusively at the semi-arid Sahelian sites of Louga and Diokoul and Gigaspora margarita was isolated only from 16.5-m and 34-m-deep samples. Comparable glomalean fungal species richness was identified in deep (1.5–34 m) and surface (0.15 m) samples. The isolation and the propagation of glomalean fungi from F. albida rhizospheres confirmed the presence of viable AM fungal propagules, down to the water table, as deep as 34 m.

Effect of the saprophytic fungus Fusarium oxysporum on arbuscular mycorrhizal colonization and growth of plants in greenhouse and field trials

Effects of the saprophytic fungus Fusarium oxysporum on arbuscular mycorrhizal (AM) colonization and plant dry matter were studied in greenhouse and field experiments. Host plants: maize (Zea mays L.), sorghum (Sorghum vulgare L.), lettuce (Lactuca sativa L.), tomato (Lycopersicum esculentum L.), wheat (Triticum vulgare L), lentil (Ervum lens L.) and pea (Pisum sativum L.), the AM fungi: Glomus mosseae, G. fasciculatum, G. intraradices, G. clarum, and G. deserticola and the carriers for F. oxysporum inoculum: aqueous solution, thin agar slices, and pellets of agar and alginate were tested under greenhouse conditions. Greatest plant growth and AM colonization responses in sterilized and unsterilized soils were observed with pea, Glomus deserticola and sodium alginate pellets as the carrier for F. oxysporum inoculum. Under field conditions, adding F. oxysporum increased the survival of transplanted pea, possibly through a beneficial effect on AM fungi. Application of F. oxysporum increased shoot dry matter, N and P concentrations of pea and sorghum plants, and the level of AM colonization attained by indigenous or introduced AM fungi. These parameters were similar in plants inoculated with either G. deserticola or with the indigenous AM fungi. Application of the saprophytic fungus increased the number of propagules of AM fungi in field plots in which pea was grown, but this increase was not sufficient to increase AM colonization of sorghum after the pea crop.

Patterns of arbuscular mycorrhiza down the profile of a heavy textured soil do not reflect associated colonization potential

Colonization of roots by arbuscular mycorrhizal (AM) fungi in several annual crops in two consecutive seasons was compared with, in the second season, the density of fungal propagules in the soil with the use of a bioassay. Root density decreased down the soil profile in both years in all crops, and a high proportion of roots were mycorrhizal throughout the profile. AM colonization decreased down the profile in cotton and lablab in the second season only. The bioassay indicated that most propagules of AM fungi in soils under cotton were located near the surface, with virtually no propagules at 1 m. The absence of propagules at depth indicates a lack of mycelium deep in the soil, and suggests that mycorrhizas are primarily initiated in the surface soil and that the fungi colonize the root system mostly through secondary spread down the profile. The use of AM colonization in the field as an indicator of propagule density and symbiotic function should be qualified by an understanding of the depth in the soil from which roots were extracted.

Production of Glomus intraradices propagules, an arbuscular mycorrhizal fungus, in an airlift bioreactor

This work addresses the symbiotic culture of the arbuscular mycorrhizal (AM) fungus Glomus intraradices with Daucus carota hairy roots transformed by Agrobacterium rhizogenes, in two submerged culture systems: Petri dish and airlift bioreactor. AM fungi play an active role in plant nutrition and protection against plant pathogens. These fungi are obligate biotrophs as they depend on a host plant for their needs in carbohydrates. The effect of the mycorrhizal roots inoculum-to-medium volume ratio on the growth of both symbionts was studied. A critical inoculating condition was observed at ∼0.6 g dry biomass (DW) · L−1 medium, above which root growth was significantly reduced when using a low-salt minimal (M) liquid medium previously developed for hairy root-AM fungi co-culture. Below critical inoculum conditions the maximum specific root growth and specific G. intraradices spore production rates of 0.021 and 0.035 d−1, respectively, were observed for Petri dish cultures. Maximum spore production in the airlift bioreactor was ten times lower than that of Petri dish cultures and obtained with the lowest inoculum assessed (0.13 g DW · L−1 medium) with 1.82 × 105 ± 4.05 × 104 (SEM) spores (g DW inoculum)−1 (L medium)−1 in 107 d. This work proposes a second-generation bioprocess for AM fungi propagule production in bioreactors. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 224–232, 1999.

Production of glomus intraradices propagules, an arbuscular mycorrhizal fungus, in an airlift bioreactor

This work addresses the symbiotic culture of the arbuscular mycorrhizal (AM) fungus Glomus intraradices with Daucus carota hairy roots transformed by Agrobacterium rhizogenes, in two submerged culture systems: Petri dish and airlift bioreactor. AM fungi play an active role in plant nutrition and protection against plant pathogens. These fungi are obligate biotrophs as they depend on a host plant for their needs in carbohydrates. The effect of the mycorrhizal roots inoculum-to-medium volume ratio on the growth of both symbionts was studied. A critical inoculating condition was observed at approximately 0.6 g dry biomass (DW). L-1 medium, above which root growth was significantly reduced when using a low-salt minimal (M) liquid medium previously developed for hairy root-AM fungi co-culture. Below critical inoculum conditions the maximum specific root growth and specific G. intraradices spore production rates of 0.021 and 0.035 d-1, respectively, were observed for Petri dish cultures. Maximum spore production in the airlift bioreactor was ten times lower than that of Petri dish cultures and obtained with the lowest inoculum assessed (0.13 g DW. L-1 medium) with 1.82 x 10(5) +/- 4.05 x 10(4) (SEM) spores (g DW inoculum)-1 (L medium)-1 in 107 d. This work proposes a second-generation bioprocess for AM fungi propagule production in bioreactors. Copyright 1999 John Wiley & Sons, Inc.

Diversity of arbuscular mycorrhizal fungus populations in heavy-metal-contaminated soils.

High concentrations of heavy metals have been shown to adversely affect the size, diversity, and activity of microbial populations in soil. The aim of this work was to determine how the diversity of arbuscular mycorrhizal (AM) fungi is affected by the addition of sewage-amended sludge containing heavy metals in a long-term experiment. Due to the reduced number of indigenous AM fungal (AMF) propagules in the experimental soils, several host plants with different life cycles were used to multiply indigenous fungi. Six AMF ecotypes were found in the experimental soils, showing consistent differences with regard to their tolerance to the presence of heavy metals. AMF ecotypes ranged from very sensitive to the presence of metals to relatively tolerant to high rates of heavy metals in soil. Total AMF spore numbers decreased with increasing amounts of heavy metals in the soil. However, species richness and diversity as measured by the Shannon-Wiener index increased in soils receiving intermediate rates of sludge contamination but decreased in soils receiving the highest rate of heavy-metal-contaminated sludge. Relative densities of most AMF species were also significantly influenced by soil treatments. Host plant species exerted a selective influence on AMF population size and diversity. We conclude based on the results of this study that size and diversity of AMF populations were modified in metal-polluted soils, even in those with metal concentrations that were below the upper limits accepted by the European Union for agricultural soils.

The effect of dazomet and fosetyl-Aluminium on indigenous and introduced arbuscular mycorrhizal fungi in commercial strawberry production

Field and outdoor pot trials were conducted to assess the compatibility of an introduced arbuscular mycorrhizal fungal (AMF) isolate Glomus fistulosum ([Skou and Jakobsen sp. nov.] BEG 31) and indigenous AMF isolate/s, with biocides frequently used in commercial strawberry production, namely dazomet and fosetyl-Al (fosetyl aluminium). In the field trial, ‘Elsanta’ plants did not exhibit any mycorrhizal colonisation by indigenous AMF spp. after soil fumigation with dazomet. Recolonisation by indigenous AMF was low one year after soil fumigation and was possibly as a result of viable indigenous AMF propagules being washed in from adjacent non-fumigated fields. The degree of colonisation by the introduced AMF isolate G. fistulosum decreased by approximately 1/2 of its original value after one year in the field. Despite fosetyl-Al application Phytophthora fragariae Hickman infection was still prevalent in ‘Elsanta’ during the trial. Although fosetyl-Al did not significantly affect mycorrhizal colonisation, % total G. fistulosum root length colonisation and the proportion of it that was arbuscular, significantly decreased with increased sampling time. In the pot trial, foliar applications of fosetyl-Al significantly reduced the percentage of AMF colonisation that was vesicular and this was independent of the number of spray applications. Fosetyl-Al did not significantly influence the metabolic activity of G. fistulosum colonisation.

AM fungal abundance and activity in a chronosequence of abandoned fields in a semiarid mediterranean site

When soils of semiarid areas are used for agriculture, their arbuscular mycorrhizal (AM) fungal propagules undergo a series of changes, and when agricultural land is abandoned it is very difficult for these populations and the plant cover to recover. We studied soils that have been abandoned for different lengths of time (3–45 years) in a homogeneous semiarid area in order to observe changes in their physical and chemical properties and in the AM fungi propagules, comparing them with soils that continue to be cultivated and a soil that has never been cultivated. The data we collected clearly showed that agricultural use reduces soil fertility and lowers AM fungi populations compared to the soil kept in its natural state. After abandonment, there is a 5‐year period when the soils undergo a greater degree of degradation after which they slowly recover, with AM fungi propagules reaching values similar to those of the virgin soil after 45 years or so. Although the physical and chemical properties followed a similar pattern of recovery, it was not possible to establish significant correlations between these parameters and the recovery of the AM fungi. Except in isolated cases, the distribution of AM fungi did not seem to be influenced by position on the landscape, with their recovery appearing to be more influenced by the presence of host plants. In this sense, the rhizosphere o/Anthyllis cytisoides showed normal values of root infection and spore numbers even during the initial stages following abandonment.

Survival of propagules of arbuscular mycorrhizal fungi in soils in eastern Australia used to grow cotton

SUMMARYSoil‐borne spores and hyphae of arbuscular mycorrhizal fungi are important propagules in cracking clay soils of northern NSW, Australia. In these soils, senescent roots were uncommon. Although c. 4–200 spores g−1 soil were found, less than 6% established arbuscular mycorrhizas in trap plants, and this percentage declined over 24 months. Using tetrazolium red as a vital stain, 16–21 % of spores from field soils were found to be viable in fresh soil and 6–7 % after 24 months of storage. Using fluorescein diacetate, the length of stained hyphae of c. 0–5 m g−1 soil was shown to be halved over 32 wk. The density of viable propagules of arbuscular mycorrhizal fungi in soil declined over time and was reduced by severe disturbance. The fungi that survived to 12 months included a species thought to form dormant spores, while those initiating infection after 24 months, did not.

Hydrocarbon pollution: its effect on native arbuscular mycorrhizal fungi (AMF)

Communities of arbuscular mycorrhizal fungi (AMF) present in two hydrocarbon polluted soils from Argentina and Germany were analyzed by examining stained pieces of plant roots for degree of colonization and fungal structures. The numbers of AMF infective propagules were also analyzed and trap cultures were established from rhizospheric soils. Colonization by AMF was higher in plants grown in non-polluted soils than in both polluted areas. In addition proportion of arbuscles to vesicles was higher in plants grown in non-polluted soil than in those grown in hydrocarbon-polluted soils. This was consistent with larger populations of AMF propagules with a potential to colonize roots in non-polluted soils. Nevertheless, AMF propagules from polluted soils also had a high colonization capacity. Glomus aggregatum and G. mosseae were isolated and identified from both polluted and non-polluted soils.

Mycorrhizae and succession in plantings of beachgrass in sand dunes

A survey of arbuscular mycorrhizal fungi (AMF), arbuscular mycorrhizae (AM), and hyphal networks of AMF was carried out in sand dune sites of different successional stages in the Province Lands Area of Cape Cod National Seashore, Massachusetts. The study focused on large‐scale plantings (each of 12–20 ha) of American beachgrass (Ammophila breviligulata) aged 0–7 yr and five adjacent natural dune areas. Sample sites ranged in vegetative cover from barren to forested. Spores of 17 species of AMF were recovered from the dunes. Over the successional sequence, there were increases in the richness and spore populations of the AMF community, the extent of colonization of A. breviligulata roots, and the mycorrhizal inoculum potential of the soil. Unvegetated sites lacked propagules of AMF, but roots of planted culms of A. breviligulata (which carried propagules of AMF) became mycorrhizal in <1 yr after planting. Spores were recovered from previously AMF‐free sites that had been planted with beachgrass for 47 wk, and five species of AMF sporulated in sites <6 yr old. Significant hyphal networks were not present in any of the planted areas (<6 yr old at the time of sampling), but did occur in natural areas. The rate of invasion of areas planted to A. breviligulata by later successional plant species may in part depend upon the establishment of a vigorous network of hyphae of AMF in a site.

Field responses to added organic matter, arbuscular mycorrhizal fungi, and fertilizer in reclamation of taconite iron ore tailing

A three season study was conducted to determine the effect of added composted yard waste, arbuscular mycorrhizal (AM) fungi, and fertilizer on plant cover, standing crop biomass, species composition, AM fungal infectivity and spore density in coarse taconite iron ore tailing plots seeded with a mixture of native prairie grasses. Plant cover and biomass, percent seeded species, mycorrhizal infectivity and spore density were greatly increased by additions of composted yard waste. After three seasons, total plant cover was also greater in plots with added fertilizer. Third season plant cover was also greater in plots amended with the higher rate (44.8 Mg ha−1) of compost than the moderate rate (22.4 Mg ha-1). Field inoculation with AM fungi also increased plant cover during the second season and infectivity during the first two seasons. Seeded native species, consisting mostly of the cover species Elymus canadensis, dominated plot vegetation during the second and third seasons. Dispersal of AM fungal propagules into nonmycorrhizal plots occurred rapidly and increased infectivity in compost-amended plots during the third season. In plots with less than 10% plant cover, AM fungal infectivity of inoculated plots was greatly reduced after the second season. The high level of plant cover and the trend of increasing proportion of mycorrhizal-dependent warm-season grasses, along with increases in infectivity, forecast the establishment of a sustainable native grass community that will meet reclamation goals.