Mycorrhizal Isolates Research Articles

Seasonal dynamics of the association between sweet potato and vesicular-arbuscular mycorrhizal fungi

To better understand the behavior of selected vesicular-arbuscular mycorrhizal (VAM) isolates in the field, we documented the growth of roots, root hairs, and VAM colonization of inoculated and noninoculated sweet potato plants (Ipomea batatas (L.) Lam. cv White Star) over a growing season. We also determined the seasonal dynamics of P and Zn uptake, and shoot and storage-root growth. Shoot cuttings were inoculated with an isolate of either Glomus etunicatum Becker and Gerdemann or Acaulospora rugosa Mortan, or were not inoculated, and were harvested 2, 4, 8, 13, 20, and 27 weeks after planting (WAP). At each harvest, roots were sampled at 0 to 30, 30 to 60, and 60 to 90 cm depths and at 0, 23, 83, and 116 cm from the base of the shoot. At the end of the study, the roots of three non-inoculated plants were sampled by soil horizon. Inoculation had no affect on shoot growth or total shoot uptake of P and Zn; shoot dry mass and P and Z content increased rapidly up to 20 WAP, while shoot length continued to increase through 27 WAP. Shoot-P concentration of plants inoculated with A. rugosa at 2 and 8 WAP were higher than the noninoculated plants, while shoot-Zn concentration was not affected by inoculation. Storage-root yields of inoculated plants were higher than yields for noninoculated plants. Root length density, and percentage of root length with root hairs and VAM colonization were highest and most dynamic near the base of the plant. Percentage of root length colonization by VAM fungi was highest in the E2 horizon, intermediate in the Bh horizon, and lowest in the Ap horizon. Percentage of root length with root hairs had the opposite pattern. Intensive measurements of root characteristics close to the base of the plant, and shoot P-content and concentration during the period of rapid yield production, provided the most useful data for evaluating the activity of effective isolates.

Comparisons of vesicular-arbuscular mycorrhizal species and inocula formulations in a commercial nursery and on diverse Florida beaches

For efficient use of mycorrhizal inoculum the effectiveness of the isolate used and the rate of application required for maximum colonization must be known. The objectives of this research were to (1) define the lower limit of inoculum density required for maximum colonization of Uniola paniculata in a commercial nursery and (2) evaluate the performance of a selected native dune vesicular-arbuscular mycorrhizal (VAM) isolate versus a commercially available non-dune VAM (foreign) isolate on three diverse Florida beaches. An inoculum-dilution study was conducted in a commercial nursery with cutroot inoculum of a Glomus sp. that had been isolated from a Florida dune. Maximum colonization was achieved with approximately 1 propagule ml-1 of growth medium. In a separate nursery study, 10 inoculation treatments (combinations of inoculum source and level) were established in the commercial nursery. Treatments included cut-root and sheared-root inoculum of the native dune isolate, and Nutri-Link, a commercial inoculum of G. intraradices. Colonized plants from selected treatments were transplanted to beach sites around Florida. At Miami Beach, after one growing season, the shoot mass of plants inoculated with the native isolate was approximately twice that of plants inoculated with the foreign isolate. At Katherine Abbey Hanna Park and Eglin Air Force Base there were no significant inoculum source effects on shoot mass or root length after one growing season. However, the native isolate produced a greater colonized root length than the foreign isolate in all plantings. The soil hyphal density was measured at Eglin Air Force Base, and the results showed that plants inoculated with the native isolate had more soil hyphae (4.33 mg-1) than plants inoculated with the foreign isolate (3.65 mg-1) or the non-inoculated plants (2.12 mg-1). Even where there were no obvious shoot growth responses, mycorrhizal inoculation may have an important effect on dune stabilization, as soil hyphae are known to bind sand grains and improve dune stability.

Mycorrhizal fungi in relation to growth and mineral nutrition of apple seedlings

The effects of two mycorrhizal fungi ( Glomus epigaeum Daniels & Trappe and Glomus macrocarpum Tul. & Tul.) on the growth and mineral composition of shoots and roots of apple seedlings ( Malus micromalus Makino) were studied. Variables were air temperature and sterilization of soil. In sterilized soil, the two species differed in their effects on seedlings grown at different temperatures. G. epigaeum was mutualistic at low and high temperature, but G. macrocarpum was ineffective at low temperature. In unsterilized soil, neither species was mutualistic at low temperature, but both increased plant growth at high temperature. In sterilized soil, mutualism by G. macrocarpum was related to colonization. Enhanced growth of seedlings was accompanied by improved uptake of immobile nutrient elements, mainly Cu, P, Zn. Apple has a high dependency on mycorrhizal fungi, and mycorrhizal isolates selected for effectiveness may be useful for producing seedlings under Chinese production conditions.

Stimulation of vesicular-arbuscular mycorrhiza by fungicides or rhizosphere bacteria

Stimulation of vesicular-arbuscular (VA) mycorrhizal fungi may secure the early establishment of symbiosis and benefit the host plant at an earlier stage of development. The application of Bacillus mycoides resulted in particular in the acceleration of early VA mycorrhiza formation. An increase in vigour of the symbiosis could be measured later in terms of increased sporulation of the mycorrhizal fungi after shoot removal. Natural sporulation during later mycorrhizal development was affected by combination of bacteria and just one mycorrhizal isolate. The stimulation of mycorrhizal development was shown to be non-specific with regard to host plant and the isolate of the VAM fungus. However, the effect could not be achieved in all combinations of soil types and host plants. Application of the systemic fungicides triadimefon and pyrazophos promoted VAM formation. Combinations of fungicide and bacterial treatments were not synergistic.

The effect of cytokinin and thidiazuron on tomato inoculated with endomycorrhiza

Seeds of tomato (Lycopersicon lycopersicum var. Peto 86) were planted in soil inoculated with two vesicular-arbuscular mycorrhizal isolates (Glomus intraradices Schenck & Smith). After 7 weeks, plants were transplanted to the field and sprayed twice with cytokinin and thidiazuron, at 50% flowering and 3 weeks later. These treatments significantly increased the percentage of infected roots (30–43%) and chlorophyll content (8–13%). Mycorrhizal plants had less carbohydrates in the roots than in the leaves. Total protein and phenylalanine contents showed pronounced increases, while proline content decreased. Treatment of the mycorrhizal plants with thidiazuron or cytokinin significantly increased plant dry weight (51–54%), and the tomato yield significantly increasecd after inoculation with both isolates (18–35% and 14–32%).

Suppression of mycorrhizal fungi in fescue by the acremonium coenophialum endophyte

Propagule population densities of the nine mycorrhizal species detected in field plots planted to tall fescue free of the Acremonium coenophialum endophyte were more than double those in plots planted to fescue heavily infected with Acremonium. Seedlings of Acremonium-free fescue detected more propagules of most of the eleven mycorrhizal species detected in a field soil than seedlings infected with Acremonium. Sporulation by three mycorrhizal isolates over 17 weeks was higher on fescue seedlings free of Acremonium than on seedlings infected with Acremonium. Since mycorrhizal fungi are believed to be confined to roots and Acremonium endophytes to shoots, the inhibitory effect of Acremonium on mycorrhizal fungi may be due to the translocation to roots of alkaloids produced by the Acremonium-Festuca symbiosis.

Electrophoretic and immunological studies on acid phosphatase from a mycorrhizal fungus of Erica hispidula L.

Wall-bound acid phosphatases of an endomycorrhizal fungus of Erica hispidula L. were separated by PAGE, electrotransferred to nitrocellulose membranes and glycoprotein characteristics studied using Concanavalin A. An antiserum was raised against the major high-molecular-weight acid phosphatase and its specificity demonstrated by immunoblotting and ELISA. The antiserum reacted very little with protein extracts of other cellular fractions and was unable to bind to wall-bound protein antigens of a mycorrhizal isolate from K. mauritanica. Ultrastructural localization of acid phosphatase by cytoenzymology and indirect immunogold labelling showed it to be almost exclusively associated with the fungal wall and septa of living hyphae, whilst in senescent hyphae it was also present within the disorganized cytoplasm.

High Root-zone Temperatures, Mycorrhizal Fungi, Water Relations, and Root Hydraulic Conductivity of Container-grown Woody Plants

Abstract High root-zone temperatures can stress container-grown plants and ultimately reduce nursery productivity in the southern United States. Water relations of glasshouse-grown Berberis thunbergii DC ‘Atropurpurea’ Buxus microphylla Seibold and Zucc japonica and Pittosporum tobira, (Thunb.) Ait. ‘Wheeler’ were studied under high-temperature root-stress conditions using container-grown plants that were either colonized with vesicular arbuscular mycorrhizal fungi (VAM) or noncolonized. Predawn xylem water potential in stems (ψstem) increased initially (more positive) in response to high root-zone temperatures (40° to 45°C), and then decreased over a 5-day period. Stomatal conductance (gs) and evapotranspiration (ET) were reduced incrementally over time in response to high root-zone temperatures. Root damage occurred, as indicated by reductions in root quality and gs at 35° and 40° for B. thunbergii and P. tobira, and at 40° and 45° for the more high-temperature-resistant B. microphylla. Colonization increased gs and ET of B. microphylla at ambient (25°) and high temperatures (45°) and increased ET of B. thunbergii at 25°. Colonized plants had lower (more negative) ψshoot with initial exposure to increased root-zone temperatures; however, throughout the remainder of the study period there was little reduction in plant stress with the mycorrhizal isolates used. Root hydraulic conductivity (Lp) increased markedly in B. thunbergii compared to B. microphylla at 40° and 45°, indicating less high-temperature resistance in B. thunbergii roots. Mycorrhizal colonization did not moderate hydraulic conductivity at high root-zone temperatures of 40° and 45°. Of the two species, mycorrhizal B. thunbergii had lower Lp at 25° and B. microphylla had lower Lp at 35°.

Effects of Two Mycorrhizal Isolates on Highbush Blueberry at Two Soil pH Levels1

Abstract Seedlings of highbush blueberry (Vaccinium corymbosum L.) subjected to 3 fungal treatments and 2 soil pH levels (4.2 and limed to 6.0) displayed no significant treatment interaction in respect to growth, mycorrhizal infection intensity, or nutrient uptake. Among the fungal treatments, there were differences in nutrient uptake and infection intensity, but no difference in total linear stem growth or number of shoots. Lower soil pH resulted in significantly greater stem growth and number of shoots; however, intensity of infection was not significantly different compared to the high pH soil.

Production of polyphenol oxidases by ectomycorrhizal fungi with special reference to Lactarius spp.

An investigation of production of polyphenol oxidase by 104 isolates of 67 species of fungi was combined with tests of their ability to form ectomycorrhizas in axenic culture. Most mycorrhizal isolates produced little or no polyphenol oxidase. However, 7 out of 8 Lactarius species produced these enzymes as vigorously as the saprophytic species tested and were insensitive to the quinones formed. These isolates were also presumed to produce cell wall-degrading enzymes since, in contrast to most other ectomycorrhizal fungi, intracellular penetration was a common feature of their mycorrhizas of birch. The possibility that Lactarius spp. are unspecialized, possibly facultative, ectomycorrhizal fungi is discussed.

The Effect of Two Mycorrhizal Fungi upon Growth and Nutrition of Avocado Seedlings Grown with Six Fertilizer Treatments1

Abstract Seedlings of ‘Topa Topa’ avocado (Persea americana Mill.) were grown in steamed loamy sand soil with no fertilizer, complete fertilizer (N, P, K, S, Ca, Mg, Cu, Zn, Mn, Fe, Mo, B), −P, −Zn, −P and −Zn, and −Zn+10 × P(640 ppm P). Seedlings were inoculated separately with one of 2 isolates of Glomus fasciculatus (Thaxter) Gerd. & Trappe (GF) or were inoculated with a water filtrate of the mycorrhizal inoculum plus autoclaved mycorrhizal inoculum. Growth of mycorrhizal seedlings was 49-254% larger than nonmycorrhizal avocados except at the −Zn+10×P regime where mycorrhizal and nonmycorrhizal avocados were of similar size. Both mycorrhizal isolates increased absorption of N, P, and Cu at all fertilizer treatments and absorption of Zn was increased with all fertilizer treatments by one mycorrhizal isolate. Fertilization with P did not alter P concentrations in leaves of nonmycorrhizal plants but increased P concentrations in leaves of mycorrhizal seedlings. Fertilization with 10×P increased P concentrations in both mycorrhizal and nonmycorrhizal seedlings. One GF isolate appeared to be superior to the other based on mineral nutrition of the host avocados. Differences between the isolates apparently were related to their rate of growth or ability to infect. Poor growth of avocado seedlings in steamed or fumigated soil can be related to poor mineral nutrition due to the destruction of mycorrhizal fungi.

Growth requirements of Rhizoctonia repens M 32

Rhizoctonia repens M 32, a mycorrhizal isolate from Orchis militaris requires both a carbohydrate (glucose or sucrose) and an amino acid (aspartic acid, glycine, serine, or glutamic acid) for growth. The fungus does not require an exogenous supply of vitamins in vitro.

Characterization and classification of mycorrhizae of Douglas fir. II. Pseudotsuga menziesii + Rhizopogon vinicolor

A common tuberculate ectomycorrhiza of Douglas fir in the Pacific Northwest, described earlier by Trappe, is further examined and defined. Tubercles consist of an outer rind of aseptate, amber, thick-walled hyphae encasing tightly packed inner elements mantled with septate, hyaline, thin-walled hyphae. Reported as a Phycomycete and a Basidiomycete, respectively, the two hyphal forms actually belong to a single fungus, Rhizopogon vinicolor A. H. Smith; cultural characteristics of this fungus are described. Pure culture mycorrhiza syntheses with both mycorrhizal and sporocarpic isolates and Douglas-fir seedlings are reported. Antagonism tests revealed the following inhibition of root pathogens by R. vinicolor: strong—Phytophthora cinnamomi Rands, Pythium debaryanum Heese, and Pythium sylvaticum Campbell & Hendrix; moderate—Fomes annosus (Fr.) Cke. and Poria weirii Murr.; and weak or none— Fusarium oxysporum f. pini (Hartig) Snyd. & Hans., Pythium ultimum Trow, Rhizoctonia solani Kuehn, and Macrophomina phaseoli (Maubl.) Ashby.