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Showing papers on "Mycelium published in 1997"


Journal ArticleDOI
TL;DR: It appears that these mycorrhizosphere interactions between bacterial and fungal plant associates contributed to the biogeochemical P cycling, thus promoting a sustainable nutrient supply to plants.
Abstract: The interactive effect of phosphate-solubilizing bacteria and arbuscular mycorrhizal (AM) fungi on plant use of soil P sources of low bioavailability (endogenous or added as rock phosphate [RP] material) was evaluated by using soil microcosms which integrated (sup32)P isotopic dilution techniques. The microbial inocula consisted of the AM fungus Glomus intraradices and two phosphate-solubilizing rhizobacterial isolates: Enterobacter sp. and Bacillus subtilis. These rhizobacteria behaved as "mycorrhiza helper bacteria" promoting establishment of both the indigenous and the introduced AM endophytes despite a gradual decrease in bacterial population size, which dropped from 10(sup7) at planting to 10(sup3) CFU g(sup-1) of dry rhizosphere soil at harvest. Dual inoculation with G. intraradices and B. subtilis significantly increased biomass and N and P accumulation in plant tissues. Regardless of the rhizobacterium strain and of the addition of RP, AM plants displayed lower specific activity ((sup32)P/(sup31)P) than their comparable controls, suggesting that the plants used P sources not available in their absence. The inoculated rhizobacteria may have released phosphate ions ((sup31)P), either from the added RP or from the less-available indigenous P sources, which were effectively taken up by the external AM mycelium. Soluble Ca deficiency in the test soil may have benefited P solubilization. At least 75% of the P in dually inoculated plants derived from the added RP. It appears that these mycorrhizosphere interactions between bacterial and fungal plant associates contributed to the biogeochemical P cycling, thus promoting a sustainable nutrient supply to plants.

355 citations


Journal ArticleDOI
TL;DR: The results suggest that qualitative effects of the AM fungal taxon on the hyphosphere, such as the nature of exudates, are more important to composition and proliferation of rhizobacteria than the quantitative development of AM soil mycelia.
Abstract: Effects of roots and of arbuscular-mycorrhizal (AM) fungi on the composition of soil bacterial colonies and the combined effects of AM fungus-rhizobacterium associations on plant and soil development are little-known. We grew sorghum (Sorghum bicolor L.) either nonsymbiotically or colonized by one of two isolates of the AM fungi Glomus etunicatum, Glomus intraradices, or Glomus mosseae. The isolates were either exotic or native to the test soil. Soils adhering (rhizosphere) or not adhering (hyphosphere) to the roots were sampled 45 days after planting. Total populations of bacteria were estimated by counting colony-forming units on a nonselective medium and grouped by colony and cell morphology. Rhizosphere populations of fluorescent pseudomonads were determined on P1 medium. Visually distinct isolates were selected for identification by Fatty-Acid-Methyl-Esther analysis; of these 25 were found to be separate species. Bacterial numbers were greater in rhizo- than in hyphosphere soil. Isolates of Bacillus and t Arthrobacter were most frequent in hyphosphere and Pseudomonas in rhizosphere soils. More bacterial species were encountered in hyphosphere than in rhizosphere soil, and bacterial communities varied within and among AM treatments. The development of the AM mycelium in soil had little influence on the composition of the microflora in the hyphosphere, while AM root colonization was positively related with bacterial numbers in the hyphosphere and with the presence of Pseudomonas in the rhizosphere. The results suggest that qualitative effects of the AM fungal taxon on the hyphosphere, such as the nature of exudates, are more important to composition and proliferation of rhizobacteria than the quantitative development of AM soil mycelia.

323 citations


Journal ArticleDOI
TL;DR: The ability of S. maltophilia W81 to protect sugar beet from Pythium -mediated damping-off was due to the production of an extracellular protease.
Abstract: Stenotrophomonas maltophilia strain W81, isolated from the rhizosphere of field-grown sugar beet, produced the extracellular enzymes chitinase and protease and inhibited the growth of the phytopathogenic fungus Pythium ultimum in vitro. The role of these lytic enzymes in the interaction between W81 and P. ultimum was investigated using Tn5 insertion mutants of W81 incapable of producing extracellular protease (W81M1), extracellular chitinase (W81M2) or the two enzymes (W81A1). Lytic enzyme activity was restored in W81A1 following introduction of a 15 kb cosmid-borne fragment of W81 genomic DNA. Incubation of P. ultimum in the presence of commercial purified protease or cell-free supernatants from cultures of wild-type W81, the chitinase-negative mutant W81M2 or the complemented derivative W81A1 (pCU800) resulted in hyphal lysis and loss of subsequent fungal growth ability once re-inoculated onto fresh plates. In contrast, commercial purified chitinase or cell-free supernatants from cultures of the protease-negative mutant WS1M1 or the chitinase- and protease-negative mutant W81A1 had no effect on integrity of the essentially chitin-free Pythium mycelium, and did not prevent subsequent growth of the fungus. In soil microcosms containing soil naturally infested by Pythium spp., strains W81, W81M2 and W81A1(pCU800) reduced the ability of Pythium spp. to colonize the seeds of sugar beet and improved plant emergence compared with the untreated control, whereas W81A1 and W21M1 failed to protect sugar beet from damping-off. Wild-type W81 and its mutant derivatives colonized the rhizosphere of sugar beet to similar extents, it was concluded that the ability of S. maltophilia W81 to protect sugar beet from Pythium -mediated damping-off was due to the production of an extracellular protease.

225 citations


Journal ArticleDOI
TL;DR: Although the mechanisms of fungal spore germination still remain unclear, new research directions emerge that will contribute answers to more general questions of cell biology.

224 citations


Journal ArticleDOI
TL;DR: The fungal neutral lipid/phospholipid ratio in the extraradical mycelium was positively correlated with the level of root infection and thus decreased with increasing applications of P, and indicated that at high P levels, less carbon was allocated to storage structures.
Abstract: The distribution of an arbuscular mycorrhizal (AM) fungus between soil and roots, and between mycelial and storage structures, was studied by use of the fatty acid signature 16:1(omega)5. Increasing the soil phosphorus level resulted in a decrease in the level of the fatty acid 16:1(omega)5 in the soil and roots. A similar decrease was detected by microscopic measurements of root colonization and of the length of AM fungal hyphae in the soil. The fatty acid 16:1(omega)5 was estimated from two types of lipids, phospholipids and neutral lipids, which mainly represent membrane lipids and storage lipids, respectively. The numbers of spores of the AM fungus formed in the soil correlated most closely with neutral lipid fatty acid 16:1(omega)5, whereas the hyphal length in the soil correlated most closely with phospholipid fatty acid 16:1(omega)5. The fungal neutral lipid/phospholipid ratio in the extraradical mycelium was positively correlated with the level of root infection and thus decreased with increasing applications of P. The neutral lipid/phospholipid ratio indicated that at high P levels, less carbon was allocated to storage structures. At all levels of P applied, the major part of the AM fungus was found to be present outside the roots, as estimated from phospholipid fatty acid 16:1(omega)5. The ratio of extraradical biomass/intraradical biomass was not affected by the application of P, except for a decrease at the highest level of P applied.

198 citations


Journal ArticleDOI
TL;DR: The occurrence of lectins in higher fungi, localisation in the sporome and mycelium, levels according to different parameters and roles in the organism are reviewed and applications of fungal lectins are discussed.

118 citations


Journal ArticleDOI
TL;DR: The higher δ15 N and %N values of the caps than of the stipes probably reflect a higher portion of proteins and amino acids in the caps, which can be a function of the N species used, the depth of soil at which the mycelium occurs, and metabolic fractionations.
Abstract: SUMMARY The 15N natural abundance and N concentrations of fruit bodies from 70 species (23 genera) of ectomycorrhizal fungi found in boreal forests are presented. Large intraspecific and intrageneric differences were found, e.g. 8.3‰15N in the species Dermocybe crocea and 12.6‰ in the genus Cortinarius. In addition, significant differences in both δ15N and %N were found between different parts of fruit bodies, with cap material giving consistently higher values. Proteins and amino acids were enriched by 9.7±0.4‰ (mean ± 1 SE) relative to chitin, irrespective of the part of the fruit body examined. Chitin had δ15N values similar to that of plant hosts. The higher δ15N and %N values of the caps than of the stipes probably reflect a higher portion of proteins and amino acids in the caps. The δ15N of mycorrhizal fungi can be a function of the N species used (organic N, NH4+, NO3−), the depth of soil at which the mycelium occurs, and metabolic fractionations. The metabolic fractionations, e.g. potential transaminations during the flux of N from the soil through the fungus to the plant, make it difficult, at present, to make inferences about sources of N based on δ15N values alone. No effect of sample drying temperature on δ15values of fungal material was detected.

118 citations


Journal ArticleDOI
TL;DR: In in vitro tests, chitosan at 1, 2, and 4% (w/v) significantly reduced the growth of Sclerotinia sclerotiorum on potato dextrose agar plates and revealed that fungal mycelium exposed to chitOSan appeared to be deformed and dead, whereas untreatedMycelium was normal in appearance.
Abstract: In in vitro tests, chitosan at 1, 2, and 4% (w/v) significantly reduced the growth of Sclerotinia sclerotiorum on potato dextrose agar plates. The effect of chitosan coating on sclerotinia rot of carrots (Daucus carota L.) held at 22°C was also investigated. Carrot roots were coated with chitosan solutions (2 or 4%) and inoculated with mycelial plugs of S. sclerotiorum culture. After 5 days of storage, chitosan at both rates reduced significantly the incidence of rot (from 88 to c. 28%) and also the lesion size (from 26 to c. 12 mm) of the rot on roots. Microscope studies revealed that fungal mycelium exposed to chitosan appeared to be deformed and dead, whereas untreated mycelium was normal in appearance.

93 citations


Journal ArticleDOI
TL;DR: Transmission and scanning electron microscopy revealed cytomorphological alterations of the hyphae treated with garlic that revealed a general increase in vacuolization and consequent reduction in the cytoplasm of the treated fungal cells.
Abstract: A study was made of the effects of garlic on the development of mycelium in the following phytopathogenic fungi: Fusarium solani (Mart.) Sacc., Rhizoctonia solani Kuhn, Pythium ultimum Trow var. ultimum, and Colletotrichum lindemuthianum (Sacc. and Magnus) Briosi and Cav. A suspension of micronized garlic powder, which has volatile organic compounds mainly consisting of linear chain aldehydes, allyl sulfides and disulfides, was used for the trials. Mycelial development of the fungi was strongly inhibited at the maximum concentration of the aqueous extract tested (100 ml/liter); however only the growth of P. ultimum var. ultimum was entirely blocked. Transmission and scanning electron microscopy revealed cytomorphological alterations of the hyphae treated with garlic. R. solani and C. lindemuthianum hyphae appeared especially collapsed, while those of F. solani were less damaged, although thinner than the control hyphae. A general increase in vacuolization was also observed, with consequent reduction in the cytoplasm of the treated fungal cells. R. solani also revealed a thickening of the cell wall, whereas C. lindemuthianum revealed a singular accumulation of osmiophil bodies immediately under the cell membrane.

89 citations


Journal ArticleDOI
Hans Ek1
TL;DR: Mycorrhizal mycelium was allowed to grow into a compartment from which roots were excluded and the respiration rate before and after nitrogen addition was measured.
Abstract: SUMMARY Mycorrhizal mycelium was allowed to grow into a compartment from which roots were excluded. Ammonium or nitrate was supplied exclusively to the fungus and the respiration rate before and after nitrogen addition was measured. Mycelial respiration in the fungal compartment represented 11-29 % of total fungal and root respiration. The mycelium in the fungal compartment received 20-29 % of shoot net assimilation, and 43-64 % of the carbon allocated to the mycelium was respired. The nitrogen-induced respiration increase ranged, in the fungal compartment, from 54 to 180 %.

87 citations


Journal ArticleDOI
TL;DR: Fungal hypaphorine had no IAA-like activity on Eucalyptus root development and therefore could not be considered as an auxin analogue; instead, a strong reduction of root hair elongation was recorded.
Abstract: The hypaphorine concentration in Pisolithus tinctorius Coker & Couch hyphae colonizing Eucalyptus roots was 3 to 5 times higher than in adjacent parts of the fungal colony. This phenomenon, observed 24 h after inoculation, was also recorded in several-month-old, well-established ectomycorrhizas. Accumulation was controlled by specific root-derived diffusible molecules: it can be induced through a membrane, but not by non-host plants. In pure culture, high hypaphorine concentration was found only in the youngest mycelium, i.e. the outer 2 mm of the colony. Fungal hypaphorine had no IAA-like activity on Eucalyptus root development and therefore could not be considered as an auxin analogue; instead, a strong reduction of root hair elongation was recorded.

Journal ArticleDOI
TL;DR: A lectin (GLL-M) was isolated from mycelia of Ganoderma lucidum using affinity chromatography on BSM-Toyopearl and another lectin was also purified from fruiting bodies of the same fungus.

Journal ArticleDOI
TL;DR: In this paper, the decolourisation of Orange II by a wood-rotting fungus has been studied, and it was found that Fungus F29 could effectively decolorise Orange II especially when grown as pelleted mycelia under agitated conditions.
Abstract: The decolourisation of Orange II by a wood-rotting fungus has been studied. It was found that Fungus F29 could effectively decolourise Orange II especially when grown as pelleted mycelia under agitated conditions. Many factors affecting the decolourisation process in nitrogen-limited media (NLM) were studied, including: concentration of glucose, NH4+, Mn(II) and veratryl alcohol; initial pH; amount of mycelium; mycelial age; Orange II concentration; temperature. Results showed that the media containing Orange II at 1000 mg dm−3 (or higher) could be decolourised by 98% of the initial colour (A480 nm) in 2 days, in most conditions tested, and that the mycelia could be repeatedly reused. © 1997 SCI.

Journal ArticleDOI
TL;DR: Seven strains of edible mushrooms were studied with regard to mycelial growth on different growth media and culture conditions, and absence of light favoured rapid mycelium development in all the strains tested.
Abstract: Seven strains of edible mushrooms were studied with regard to mycelial growth on different growth media and culture conditions. Medium WDA (wheat/dextrose/agar) promoted higher rates of mycelial growth for all the mushrooms investigated. The majority of the strains presented higher growth rates at 30°C, but only Lentinus edodes kept maximum rates at low pH (pH 4.0), followed by Stropharia rugosoannulata and Pleurotus ostreatus (pH 5.0). Absence of light favoured rapid mycelium development in all the strains tested.

Journal ArticleDOI
TL;DR: In this article, four white rot fungi, including two strains of Pleurotus sp., one Dichomitus squalens, and one Ganoderma applanatum, were grown on milled straw.
Abstract: Four strains of white rot fungi, including two strains of Pleurotus sp., one Dichomitus squalens, and one Ganoderma applanatum, were grown on milled straw. After colonization of the straw by the fungi, sterile or nonsterile plugs of soil were added to the fungal substrates. The influence of the sterile soil and the indigenous soil microbiota on fungal growth, overall respiration, and production of ligninolytic exoenzymes was assessed. A method for extraction of laccase from soil samples was developed. Lignocellulose decomposition, and enzyme production of D. squalens were enhanced by the presence of sterile soil. The availability of inorganic compounds such as manganese may be a trigger for this stimulation. Neither growth nor the production of laccase and manganese peroxidase (MnP) of the Pleurotus strains was markedly affected by the soil microbiota. These fungi were highly competitive with the soil microbiota. It was demonstrated for the first time that the exoenzymes of such fungi are active in nonsterile soil. Enzyme activity in the aqueous phase of soil was high as in the aqueous phase of the straw substrate. D. squalens and G. applanatum did not withstand the competition with the soil microbiota, but the mycelia associated with straw were overgrown by soil microorganisms. Correspondingly, the fungi did not penetrate the soil, decomposition of lignocellulose was impeded, and the activities of laccase and MnP decreased dramatically.

Journal ArticleDOI
TL;DR: Of the two potato glycoalkaloid-containing liquid medium from R. solani cultures, α-chaconine was the more inhibitory on spore germination in Alternaria brassicicola and Phoma medicaginis, and on growth in liquid culture of these species and also Ascobolus crenulatus and Rhizoctonia solani.

Journal ArticleDOI
TL;DR: It is suggested that apoplastic chitinases in the root cortex destroy elicitors from the ectomycorrhizal fungi without damaging the fungus.
Abstract: Two chitinases (EC 3.2.1.14) and two [beta]-1,3-glucanases (EC 3.2.1.39) were purified from the culture medium of spruce (Picea abies [L.] Karst.) cells to study their role in modifying elicitors, cell walls, growth, and hyphal morphology of ectomycorrhizal fungi. The 36-kD class I chitinase (isoelectric point [pl] 8.0) and the 28-kD chitinase (pl 8.7) decreased the activity of elicitor preparations from Hebeloma crustuliniforme (Bull. ex Fries.) Quel., Amanita muscaria (L.) Pers., and Suillus variegatus (Sw.: Fr.) O.K., as demonstrated by using the elicitor-induced extracellular alkalinization in spruce cells as a test system. In addition, chitinases released monomeric products from the walls of these ectomycorrhizal fungi. The [beta]-1,3-glucanases (35 kD, pl 3.7 and 3.9), in contrast, had little influence on the activity of the fungal elicitors and released only from walls of A. muscaria some polymeric products. Furthermore, chitinases alone and in combination with [beta]-1,3-glucanases had no effect on the growth and morphology of the hyphae. Thus, it is suggested that apoplastic chitinases in the root cortex destroy elicitors from the ectomycorrhizal fungi without damaging the fungus. By this mechanism the host plant could attenuate the elicitor signal and adjust its own defense reactions to a level allowing symbiotic interaction.

Journal ArticleDOI
TL;DR: Whole tobacco plants treated with GP 34 through their roots showed an enhanced lipoxygenase activity as well as hydroxyproline-rich glycoprotein accumulation, indicating that this molecule had elicitor properties.
Abstract: A glycoprotein of 34 kDa (GP 34) was solubilized at acidic pH from the mycelium of Phytophthora parasitica var. nicotianae and was purified by ion exchange and gel permeation chromatography. Whole tobacco plants treated with GP 34 through their roots showed an enhanced lipoxygenase activity as well as hydroxyproline-rich glycoprotein accumulation, indicating that this molecule had elicitor properties. An antiserum raised against the pure glycoprotein allowed localization of GP 34 by immunogold-labeling on the cell surface of the mycelium when the fungus was grown in vitro. In the wall-less zoospores, GP 34 was limited to the flagellum surface. It was then abundantly synthesized at the onset of encystment. During infection of tobacco plants, labeling was very faint at early stages of colonization, particularly in the susceptible host cultivar. It appeared earlier in the resistant host cultivar and was restricted to the living fungus, declining with mycelium cell death.

Journal ArticleDOI
TL;DR: It was revealed that H. ericae was able to produce significantly higher yield when grown on intact fungal necromass than when provided with equivalent concentrations of N in the form of ammonium.
Abstract: SUMMARY Measurements of the chitin content of the rooting horizons of a typical mor-humus heathland soil, indicate that chitin can contain in excess of 20 % of the total nitrogen in the litter (L) horizon and 30 % in the fermentation (F) horizon. Much of this chitin-nitrogen is thought to be contained in the mycelial walls of soil fungi. Experiments were therefore designed to test the hypothesis that such sources of N could be rendered accessible to the ericaceous plants by their fungal endophytes. Mycelium of the ericoid endophyte Hymenoscyphus ericae (Read) Korf & Kernan and of the ectomycorrhizal fungus Suillus bovinus (Fr.) 0. Krantze were grown in liquid culture before being killed and added either in the intact condition, or after fractionation, as sole sources of N to sterile media upon which were grown H. ericae in pure culture, or mycorrhizal and non-mycorrhizal plants of Vaccinium macrocarpon Ait. and Calluna vulgaris L. The abilities of the test organisms to utilize the nitrogen contained in the intact mycelial necromass, or in its fractions, were assessed by determining their yields and nitrogen concentrations of their tissues. It was revealed that H. ericae was able to produce significantly higher yield when grown on intact fungal necromass than when provided with equivalent concentrations of N in the form of ammonium. Its yields on mycelial fractions were lower, but still significantly greater than those obtained in the controls lacking N. Significantly greater yields and N contents were also found in the ericaceous plants grown with these nitrogenous substrates in the mycorrhizal condition. Without H. ericae they had no access to the substrates. The possible ecological implications of these results are discussed.

Journal ArticleDOI
TL;DR: The results suggest that the interior of the root is a key site for implementation of the strain’s biocontrol activity against soilborne plant-pathogenic fungi.
Abstract: Pseudomonas fluorescens CHA0 protects plants from damage caused by several soilborne fungi. In this work, immunofluorescence microscopy was used to investigate the colonization of tobacco roots by CHA0 and its physical relationship with the black root rot fungus Thielaviopsis basicola. The pseudomonad colonized the rhizoplane shortly after planting of tobacco seedlings in sterile soil microcosms, in which it had been introduced as soil inoculant. CHA0 was found between and inside cells in the epidermis and the cortex, as well as in the xylem vessels, within 4–7 days after planting of seedlings. The presence of CHA0 delayed the colonization of the interior of tobacco roots by T. basicola compared with the treatment in which only the fungus had been inoculated. Likewise, the pseudomonad reduced the extent of black root rot from 82% to 28%. However, CHA0 was seldom found in contact with the mycelium of T. basicola or in its vicinity, indicating that direct colonization of the mycelium of T. basicola by CHA0 was not required for protection of tobacco against black root rot. Overall, the results suggest that the interior of the root is a key site for implementation of the strain’s biocontrol activity against soilborne plant-pathogenic fungi.

Journal ArticleDOI
TL;DR: Although interactions between microorganisms and silicon have been generally neglected, the results show that silicon compounds can increase fungal growth under both oligotrophic and nutrient-rich conditions.

Journal ArticleDOI
TL;DR: The ability of the white rot basidiomycete Phanerochaete chrysosporium to transform s-triazine herbicides has been investigated in laboratory experiments and atrazine transformation was found to be supported by the mycelium, which contained significant amounts of microsomal cytochrome P450.
Abstract: The ability of the white rot basidiomycete Phanerochaete chrysosporium to transform s-triazine herbicides has been investigated in laboratory experiments. The chlorinated metabolites formed during atrazine N-dealkylations were not further transformed by the fungus, whereas hydroxyatrazine was converted to an unknown product. P. chrysosporium was also able to carry out the N-dealkylation of the herbicides simazine, propazine and terbuthylazine. Herbicide metabolism was not supported by purified peroxidases. The highest rates of herbicide N-dealkylation were obtained in liquid cultures maintained under moderate temperature allowing a long mycelium growing phase. Atrazine transformation was found to be supported by the mycelium, which contained significant amounts of microsomal cytochrome P450. Herbicide N-dealkylation was decreased in the presence of 1-aminobenzotriazole, in agreement with the involvement of P450 monooxygenases in atrazine metabolism.

Journal ArticleDOI
TL;DR: The systemic fungicides propiconazole and carbendazim had similar effects on all three fungal species, although P transport efficiency and SDH activity differed markedly between the fungi.
Abstract: The influence of the systemic fungicides propiconazole (Tilt 250E) and carbendazim (Bavistin) at field application rates on the functioning of three arbuscular mycorrhizal fungi was studied. Short-term fungal 32P transport and succinate dehydrogenase (SDH) activity in external hyphae of Glomus intraradices Schenck and Smith, G. claroideum Schenck and Smith and G. invermaium Hall in symbiosis with pea (Pisum sativum L.) were measured. In the experimental system used, the hyphae grew into two root-free hyphal compartments (HCs). The fungicides were applied to each HC 24 days after sowing and 32P was added to one HC of each pot. Four days later, the fungicide effect on fungal P transport was measured as the difference in 32P content of treated and untreated plants. SDH activity in fungal hyphae was determined in the HCs given no 32P. Carbendazim severely inhibited 32P transport and SDH activity in external hyphae at an application rate of 0.5 μg g–1 soil. The ergosterol inhibitor propiconazole affected none of these parameters. The fungicides had similar effects on all three fungal species, although P transport efficiency and SDH activity differed markedly between the fungi.

Journal ArticleDOI
TL;DR: In this paper, the degradation of chlorophenols by P. chrysosporium in static cultures has been studied and the influences of mycelium acclimation, co-substrate concentration and nitrogen source on phenol degradation were analyzed.

Journal ArticleDOI
TL;DR: In this article, two approaches are presented to estimate mycelium location of fungi in a coniferous forest in Bavaria, Germany, using soil and mushroom samples from the same soil horizon and year.

Journal ArticleDOI
TL;DR: Overwinter survival of mycelia would enable plants to become incorporated into functional mycorrhizal associations early in spring, and was not dependent on either the presence of root pieces or on the connection ofMycelia to roots.
Abstract: SUMMARY Abuscular mycorrhizal fungi are thought to survive adverse environmental conditions primarily as spores. Extraradical mycelia of two Glomus species were produced in fine mesh pouches which excluded roots but not hyphae. The mycelia in these pouches were exposed to freezing conditions, either in the field or in a controlled–temperature chamber. Bioassay plants were grown directly in the pouches and mycorrhizal colonization was assessed after 1 month. The mycelia remained infective in frozen soil over winter. This survival was not dependent on either the presence of root pieces or on the connection of mycelia to roots. Spores were not an effective inoculum in these bioassays. Overwinter survival of mycelia would enable plants to become incorporated into functional mycorrhizal associations early in spring.

Journal ArticleDOI
TL;DR: The usefulness of the internal transcribed spacer (ITS)-5.8S can be used as a specific probe for the estimation of fungal or plant rRNA in the symbiotic tissues and to determine whether an mRNA is down- or up-regulated in ectomycorrhiza.
Abstract: Ectomycorrhiza is a complex association of several types of plant and fungal cells. Differentiation of symbiotic structures is correlated with large changes in mRNA synthesis, leading to novel protein patterns. Quantification of up- and down-regulated specific transcripts is complicated by the intermingling of root and hyphal components. Determination of steady-state levels of symbiosis-regulated mRNA requires a normalization to the housekeeping RNA content of each partner. In this study, the usefulness of the internal transcribed spacer (ITS)-5.8S ribosomal DNAs (rDNAs) as molecular markers of the root colonization by fungal mycelium was assayed. The rDNA ITSs of Pisolithus tinctorius and Eucalyptus globulus were cloned by PCR amplification, and their sequences were determined. They contained the 5.8S rDNAs, and these two probes did not cross-hybridize. Steady-state levels of the ITS-5.8S rRNAs in the vegetative mycelium, in the noninfected root, and in ectomycorrhizas of E. globulus-P. tinctorius 441 were estimated at different stages of development. Colonization of roots by the mycelium provoked a large decrease in the proportion of root rRNAs. At the end of mycorrhiza formation, about 80% of the ectomycorrhizal RNA belonged to the mycobiont. The ITS-5.8S can be used as a specific probe for the estimation of fungal or plant rRNA in the symbiotic tissues and to determine whether an mRNA is down- or up-regulated in ectomycorrhiza.

Journal ArticleDOI
TL;DR: Results suggest that mycelium in plant debris may play a role as primary inoculum of the disease in the Philippines.
Abstract: Plant debris floating on the water surface after puddling was collected and applied in a sclerotia-free experimental field to confirm that mycelia in plant debris act as primary inocula for rice sheath blight in the Philippines. As we were able to isolate sheath blight fungus from plant debris, the mycelium apparently survived in debris until the following growing season. The percentage of diseased hills in plots without plant debris reached 3.9% by one month after heading, whereas in plots containing plant debris at a rate of 2kg and 4kg per 35m2, the values were 11% and 18%, respectively. Inoculum potential of sclerotia was about three times as much as that of plant debris. These results suggest that mycelium in plant debris may play a role as primary inoculum of the disease in the Philippines.

Journal ArticleDOI
TL;DR: Results indicate that AOL functions as a storage protein during both saprophytic and parasitic growth.
Abstract: It was recently shown that the nematode-infecting fungus Arthrobotrys oligospora contains a saline-soluble lectin (designated AOL) that is a member of a novel family of fungal lectins sharing similar primary sequences and binding specificities. During saprophytic growth in liquid cultures, levels of AOL and AOL mRNA were found to vary depending on the growth phase of the mycelium and the carbon/nitrogen (C/N) ratio of the medium. AOL was not detected in young mycelium. In older mycelium (stationary growth phase) grown in media with low C/N ratios (1 or 6), AOL comprised 5-20% of the total amount of saline-soluble proteins present in the mycelium. Neither the lectin nor its transcript was detected in mycelia grown in medium with higher C/N ratios (≥150). Under conditions of nitrogen starvation, AOL was preferentially degraded in relation to the total amount of saline-soluble proteins present in the mycelium. During the infection of nematodes, the level of AOL protein and AOL mRNA increased significantly once the nematodes had been penetrated and digested. Large amounts of AOL accumulated in the trophic hyphae growing inside the nematode as visualized by immunofluorescence microscopy. Later, AOL labelling was detected outside the digested nematodes, preferentially in strands of aggregated hyphae and in newly developed trap cells. Electron microscopy showed that AOL was localized to the cytoplasm and the nucleus of both vegetative mycelium and trap cells, and in the trophic hyphae growing inside the infected nematodes. These results indicate that AOL functions as a storage protein during both saprophytic and parasitic growth.

Journal ArticleDOI
TL;DR: The experiment did not support the hypothesis that phytate, which has a low solubility in soils, is a useful P source for ectomycorrhizal plants, and the addition of a relatively high concentration of a solublephytate to the growth substratum resulted in an increased relative growth rate (RGR) in both mycor rhizal and non-mycorrhIZal plants.
Abstract: 1. The external mycelia of the ectomycorrhizal fungi Thelephora terrestris and Suillus luteus, associated with Pinus sylvestris roots, exhibited a substantial extracellular acid phosphatase activity. The activity was positively correlated with the ergosterol concentration in the growth substratum and decreased with an increasing P nutrition. 2. The pioneer species T. terrestris grew best at a high Pi nutrition level whereas S. luteus, a ‘late-stage’ mycobiont, produced more active biomass at a low Pi nutrition level. 3. The phytase activity of the external mycelia could not be detected; at the root surface a phytase activity was observed. Mycorrhizas had significantly higher activities than uninfected roots. 4. The addition of a relatively high concentration of a soluble phytate to the growth substratum resulted in an increased relative growth rate (RGR) in both mycorrhizal and non-mycorrhizal plants. The influence of the mycorrhizal fungi on the use of the phytate-P was small, despite the phytase activity of the mycorrhizal feeder roots. 5. The addition of phytate fixed on a HPLC resin did not result in an increase of the RGR and P uptake neither in the non-mycorrhizal nor in the mycorrhizal Pines. The experiment did not support the hypothesis that phytate, which has a low solubility in soils, is a useful P source for ectomycorrhizal plants.