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Background This work aimed at characterizing 12 isolates of the genus Tuber including Tuber melanosporum (11 isolates) and Tuber brumale (one isolate). This was done using internal transcribed spacer (ITS) sequences, confirming their origin. Results Analysis of their mating type revealed that both MAT1-1 and MAT1-2 exist within these isolates (with 3 and 8 of each, respectively). We observed that each of these cultures was consistently associated with one bacterium that was intimately linked to fungal growth. These bacterial associates failed to grow in the absence of fungus. We extracted DNA from bacterial colonies in the margin of mycelium and sequenced a nearly complete 16S rDNA gene and a partial ITS fragment. We found they all belonged to the genus Rhodopseudomonas, fitting within different phylogenetic clusters. No relationships were evidenced between bacterial and fungal strains or mating types. Rhodopseudomonas being a sister genus to Bradyrhizobium, we tested the nodulation ability of these bacteria on a promiscuously nodulating legume (Acacia mangium), without success. We failed to identify any nifH genes among these isolates, using two different sets of primers. Conclusions While the mechanisms of interaction between Tuber and Rhodopseudomonas remain to be elucidated, their interdependency for in vitro growth seems a novel feature of this fungus. Electronic supplementary material The online version of this article (doi:10.1186/s40064-016-2756-6) contains supplementary material, which is available to authorized users.

We examined the below-ground mycorrhizal diversity of P. pinea seedlings inoculated with S. collinitus six years after out- planting in a disturbed site, located at La Petite-Camargue (Gard, France). This was performed using the polymerase chain reaction (PCR), the restriction fragment length polymorphism (RFLP) and the sequencing of the nuclear ribosomal internal transcribed spacer (ITS). Seven and one plants corresponding, respectively, to inoculated and non-inoculated (control) treatments were chosen randomly. Examinations were carried out directly from ectomycorrhizae. A total number of 233 root tips was examined. Five ITS RFLP taxa were detected. The ITS taxon I corresponded to the ectomycorrhizal species Rhizopogon rubescens. This fungus was abundant (55%) in the P. pinea ectomycorrhizal community. The other ITS taxa were rare and remained unidentified. The current P. pinea plantation showed a restricted diversity of the ectomycorrhizal community which is typical of ectomycorrhizal communities in young plantations established in disturbed stands.

Summary The study about Hebeloma cylindrosporurrfs acid phosphatase activity according to the phosphorus content of the culture medium, has been realised by using a new staining: the lanthanum. Electron energy loss spectroscopy (EELS) and electron spectroscopy imaging (ESI) have been used to verify the presence of the stain. These technicals display a heterogeneous acid phosphatase ativity on the plasmalemma. The phosphorus deficienced mycelium presents an excreted acid phosphatase activity only in the storage section. Acid phosphatases are detected on the plasmalemma, the tonoplast, the polyphosphate granules and the lipid globuls. Whatever the phosphorus content it is, the walls are stainless.

International audience; The phylogenetic relationships among 200 Pisolithus basidiomata collected from pine, oak, and eucalypt forests and rockrose scrubs in Morocco were investigated. Using PCR-RFLP analysis of the internal transcribed spacer (ITS) of ribosomal DNA, this collection could be divided into 5 groups, by using PCR-RFLP analysis of the internal transcribed spacer (ITS) of ribosomal DNA. The ITS of a representative basidioma of each group was sequenced, and a phylogenetic analysis was performed. The dendrogram suggests that at least five Pisolithus species are present in Morocco. Pisolithus basidiomata collected in the Pinus and Quercus forests correspond to Pisolithus arrhizus and P. species 4 as previously described by Martin and colleagues in 2002. Those collected from the eucalyptus forests, under E. gomphocephala and E. camaldulensis, correspond to P. albus and P. microcarpus. Basidiomata collected from the rockrose scrubs, under Cistus crispus, C. monspeliensis or C. salviifolius, are all identified as Pisolithus species 3. Phylogenetic analyses showed that our different Pisolithus grouped well with Pisolithus specimens from other geographical origins.

Summary The study examined the diversity of ectomycorrhizal fungi, naturally established on roots of containerised Pinus seedlings in a nursery, using PCR–RFLP and sequencing of the nuclear ribosomal internal transcribed spacer. Seventy-two samples, including ectomycorrhizae and fruit bodies, were examined. Molecular typing assigned the fungal symbionts to four ectomycorrhizal Boletales: Rhizopogon rubescens , Suillus bovinus , S. variegatus , and R. luteolus. R. rubescens was abundant (37.5%), while Suillus and R. luteolus species were moderately established (25–26%) and rare (2.8%), respectively. In addition, Rhizopogon species colonised P. nigra ssp. salzmannii seedlings , whereas Suillus species were identified on Pinus nigra ssp. nigra seedlings. The diversity and the ability of these naturally established symbionts under artificial nursery conditions were discussed. The molecular survey investigated here should contribute to successful monitoring of mycorrhizal application under both nursery and plantation conditions.

Ectomycorrhizal diversity (ED) associated with Pinus halepensis trees was examined 1.5 years after outplanting at a fire-disturbed site of Rieucoulon (Herault, France). ED analysis was examined on non-inoculated and Suillus collinitus-inoculated plants, and on naturally regenerated trees. A total of 461 single ectomycorrhizas was typed using PCR-RFLP analysis and sequencing of the internal transcribed spacer ( ITS) of the nuclear rDNA. Twelve ITS RFLP-taxa were detected. The ectomycorrhizal fungus S. collinitus ( ITS RFLP-taxon 1) was the most abundant (45.8 - 59.7%) species in the three treatments, suggesting that it is a strong ectomycorrhizal competitor in this site. S. mediterraneensis ( ITS RFLP-taxon 2) was restricted to control and naturally regenerated trees and was unequally moderate (11.7 - 31.9%). The remaining below-ground ITS RFLP-taxa were uncommon and rare (0.0 - 9.6%). The current experimental P. halepensis plantation showed a species-poor community dominated by two Suillus species. Ecological strategies of these symbionts are discussed., Diversité ectomycorhizienne dans une plantation à Pinus halepensis. La diversité génétique des ectomycorhizes de plants de P. halepensis a été examinée une année et demie après introduction dans un site incendié de Rieucoulon (Hérault, France). Cette diversité a été caractérisée à l’aide du polymorphisme de fragments de restriction (RFLP) et du séquençage de l’espaceur interne transcrit (ITS) de l’ADN ribosomal nucléaire. Trois traitements ont été examinés : des plants témoins, des plants mycorhizés avec Suillus collinitus et des plants en régénération naturelle. Au total, 461 ectomycorhizes ont été soumises au typage moléculaire. Douze ribotypes d’ITS ont été détectés. S. collinitus (ribotype 1) est l’espèce dominante (45,8–59,7 %) dans les trois traitements suggérant une forte capacité de colonisation dans ce site. La présence de S. mediterraneensis (ribotype 2) est limitée aux plants témoins et aux autres issus de la régénération naturelle et sa fréquence est modérée (11,7–31,9 %). Les autres symbiotes ectomycorhiziens sont rares (0,0–9,6 %) et leur abondance diffère d’un traitement à l’autre. Cette étude révèle une faible diversité des symbiotes ectomycorhiziens dans la plantation à P. halepensis; elle est dominée par deux espèces du genre Suillus. Les stratégies écologiques de ces symbiotes sont discutées.

The effect on plant growth of pre-inoculation of Pinus sylvestris with the ectomycorrhizal (ECM) edible basidiomycete Lactarius deliciosus (isolate D45) under controlled conditions, and the development on roots of this basidiomycete, were investigated in gamma-irradiated and unsterilized containers containing different forest soil cores or a perlite-vermiculite mixture. Five months after planting, L. deliciosus mycorrhizal plants exhibited greater growth than the non-mycorrhizal ones in all soil types, i.e. up to a 325% increase in shoot height in the sterilized soils. The experiment demonstrated the dependency of P. sylvestris seedlings upon ECM symbiosis for their survival in gamma-irradiated, microbiologically disturbed soil samples. Furthermore, in two soils, the growth of L. deliciosus-inoculated seedlings was greater in the sterilized soil samples than in the non-sterilized ones, i.e. 46% and 132% increase in shoot height under sterilized soil conditions. In containers randomly sampled from each soil type, the degree of root colonization by the inoculated isolate, calculated as the number of mycorrhizal root tips divided by the total number of root tips x100, ranged from 80% to 35%. Within the short term, the inoculated isolate developed rapidly on roots, dominated, and hampered ectomycorrhiza formation by various unidentified (but not Lactarius) resident ECM fungi in unsterilized soil types. Results indicate that the ECM species L. deliciosus is worth investigating to ascertain if other isolates benefit pine growth like the isolate D45, and are therefore also attractive candidates for forestry applications in the Mediterranean area.

International audience; Ectomycorrhization of Cedrus atlantica seedlings under controlled conditions: Efficiency of two forms of mycelial inocula. The effect of two mycelial inocula (mycelia grown in peat-vermiculite saturated by a nutritive medium, or entrapped into alginate) of two ectomycorrhizal species (Tricholoma tridentinum var. cedretorum and Hebeloma sinapizans) was tested, under controlled conditions, on the mycorrhization of Cedar seedlings grown on mineral substrate. One year after inoculation, the percentage of infected root tips and root ergosterol contents were higher with cedars inoculated using T. tridentinum peat-vermiculite inoculum than using alginate one. The opposite results were obtained with H. sinapizans. The degrees of mycorrhization of the seedlings inoculated with T. tridentinum were higher than those of the seedlings inoculated with H. sinapizans. The mycorrhization of Cedrus atlantica seedlings using mycelial inocula was thus performed under controlled conditions which may be reproducible. The consequences of the inoculation of seedlings on their shoot and/or root biomass vary with the inoculum form and fungal species.; L'effet de la forme de l'inoculum (obtenu sur tourbe-vermiculite ou par inclusion dans l'alginate) de Tricholoma tridentinum var. cedretorum et Hebeloma sinapizans sur la mycorhization de semis du Cèdre de l'Atlas, cultivés sur un substrat minéral, a été expérimenté en conditions contrôlées. L'utilisation de mycélium de T. tridentinum développé sur tourbe-vermiculite permet d'obtenir des degrés de mycorhization supérieurs à ceux enregistrés en employant du mycélium du même champignon inclus dans l'alginate, un an après l'inoculation. Le résultat inverse a été obtenu avec H. sinapizans. Les pourcentages d'apex mycorhizés et les teneurs en mycélium viable des racines des plants inoculés par T. tridentinum ont été supérieurs à ceux des plants inoculés avec H. sinapizans. L'obtention de mycorhizes à l'aide d'inocula mycéliens, a été réalisée sur le Cèdre de l'Atlas dans des conditions contrôlées et reproductibles. L'inoculation des semis par du mycélium d'H. sinapizans cultivé sur substrat solide a stimulé la biomasse de leurs parties aériennes et racinaires alors que l'inoculum de T. tridentinum, produit sur le même substrat, n'a permis d'augmenter significativement que la biomasse des racines. L'inoculation des plants par du mycélium d'H. sinapizans inclus dans l'alginate n'a été bénéfique que pour la biomasse de leurs parties aériennes.

Effects of nitrogen (N) source and concentration on root system architecture and receptivity to mycorrhizal infection were studied in seedlings of Atlas cedar (Cedrus atlantica Manetti) grown in root observation boxes in a controlled-environment chamber. Nitrogen was supplied in a solution containing either NO3-; or NH4+ at a concentration of either 0.25 or 5.0 mM. Root extension was recorded twice weekly by tracing the roots growing in contact with the transparent face of the root observation box. Among treatments, lateral root production and branching density were greatest with 5.0 mM NO3-. Inoculation with mycelium of Tricholoma cedrorum Malencon was carried out 3 months after the start of the N treatments. The highest percentage of mycorrhizal roots, and the greatest amounts of living mycelium (estimated by the ergosterol assay) were observed in the NO3- treatments. Differences in root branching density among the N treatments were insufficient to explain the observed differences among treatments in the extent of mycorrhizal infection of seedlings.

International audience; Effects of P-fertilization on the mycorrhization, growth and nutrition (P, N) of Cedrus atlantica Manetti seedlings inoculated in nursery with mycelia of Tricholoma tridentinum Sing. var. cedretorum Bon. In order to study the effects in nursery of phosphorus fertilization on the growth and the mycorrhizal infection of Cedrus atlantica Manetti by Tricholoma tridentinum, seedlings grown in containers have been inoculated and fertilized with three nutrient solutions containing 0, 43.4 or 86.8 mg l$^{-1}$ of P. Six months after inoculation, the percentages of mycorrhizal root tips were determined and the total and viable mycelium contents in the roots were estimated by fungal glucosamine and ergosterol assay, respectively. The highest degree of mycorrhizal infection was obtained in seedlings fertilized with 43.4 mg l$^{-1}$ P. Fertilisation with 86.8 mg l$^{-1}$ P reduced significantly the percentage of mycorrhizal root tips, the total and viable mycelium contents in roots obtained with 43.4 mg l$^{-1}$ P. Mycorrhization of seedlings did not significantly affect neither their growth nor their phosphorus and nitrogen contents. Quality of seedlings correspond to the norms required for the production of containerized Cedar seedlings.; Afin d'étudier les effets en pépinière de la fertilisation phosphatée sur la croissance et la mycorhization de Cedrus atlantica Manetti par Tricholoma tridentinum, des semis cultivés pendant deux mois et demi en conteneurs ont été inoculés puis fertilisés pendant 10 semaines avec une solution nutritive contenant 0, 43,4 ou 86,8 mg l$^{-1}$ de phosphore (P). Six mois après l'inoculation, les pourcentages d'apex mycorhizés ont été déterminés et les teneurs en mycélium total et viable des racines ont été estimées respectivement par les dosages de la glucosamine fongique et de l'ergostérol. Les degrés de mycorhization par T. tridentinum les plus élevés ont été obtenus avec 43,4 mg l$^{-1}$ de P. Une fertilisation en P de 86,8 mg l$^{-1}$ a réduit significativement le pourcentage d'apex racinaires mycorhizés et les teneurs des racines en mycélium total et viable obtenus avec un apport de modéré de P (43,4 mg l$^{-1}$). La mycorhization des cèdres par T. tridentinum n'affecte significativement ni leur croissance, ni leurs contenus en phosphore et en azote. La qualité des plants est conforme aux normes requises pour les cèdres produits en conteneurs dans la région méditerranéenne française.

The mycorrhizal relationships between pines and two edible species of Lactarius sect. Dapetes were investigated by optimizing the experimental conditions of mycelial growth and of mycorrhizal colonization of pine seedlings. In vitro mycelial growth of Lactarius deliciosus and L. sanguifluus was improved on a buffered medium containing glucose, amino acids, and vitamins. Two methods of mycorrhization of pines with Lactarius deliciosus were tested. The mycorrhizal colonization was rapid and intense under non-aseptic conditions with a low nutrient supply and without exogenous glucose. A positive influence of mycorrhizal colonization on Pinus sylvestris growth was subsequently observed. Under axenic conditions and with a high nutrient supply, mycorrhization was stimulated at 10 g/L of exogenous glucose, irrespective of the phosphorus concentration. At high phosphorus level (1 mM) and 0.1, 1.0, or 10.0 g/L glucose, growth of Pinus sylvestris was reduced by inoculation. Stability and development of Pinus spp./Lactarius deliciosus symbioses were assayed in a climatic chamber using containers filled with a synthetic substrate. Over a 2-year culture period, the root systems of the pine seedlings were heavily colonized by Lactarius deliciosus. One year following inoculation, Lactarius deliciosus fruit-body primordia appeared associated with Pinus sylvestris seedlings. Six months later, two mature basidiomata were obtained. This is the first report of soilless fruit-body formation of this edible mushroom.Key words: ectomycorrhiza, inoculation, Lactarius deliciosus, Lactarius sanguifluus, Pinus, wild edible mushrooms.

International audience

International audience

International audience

Plusieurs types de mycorhizes sont distingues, essentiellement selon leur structure et la position systematique des partenaires. Parmi ces types, les ectomycorhizes se rencontrent chez des especes ligneuses dont l’interet economique et sylvicole est considerable. Sur les racines des pins, ces organes se caracterisent par leurs formes courtes et epaisses, simples ou ramifiees dichotomiquement et diversement colorees. L’etablissement de la symbiose entraine une modification plus ou moins nette de la morphologie du systeme racinaire et de son environnement biotique ainsi que du fonctionnement de la plante-hote. Ainsi, les complexes ectomycorhiziens sont susceptibles de faciliter l’absorption de l’eau et des elements mineraux par la plante-hote et d’augmenter sa tolerance a des facteurs du sol tels que le calcaire, les metaux lourds et les agents pathogenes.

International audience

General aspects of the structure of forest tree mycorrhizae and of the physiological and ecological consequences of the establishment of symbiosis are reviewed. A long-term research programme on the use of controlled mycorrhizal infection to improve the quality of the forest seedlings and mediterranean reafforestation is described, and preliminary results are presented : obtention of mycorrhizal isolates suitable for mediterranean forest species ; screening of these isolates using physiological criteria ; production of mycorrhizal seedlings and characterisation of the mycorrhizae ; measurement of the physiological effects of mycorrhizal infection in the nursery ; definition of the ecological ability of selected isolates ; set-up and follow-up of the ecology and ecophysiology of the experimental wood lots., Les aspects généraux de la structure des mycorhizes associées aux arbres forestiers et les conséquences physiologiques et écologiques de l'établissement de la symbiose sont revus. Un programme de recherche à long terme sur l'utilisation de la mycorhization contrôlée pour améliorer la qualité des jeunes plants forestiers et des reboisements méditerranéens est décrit. Les premiers résultats sont présentés : obtention d'isolats mycorhiziens compatibles avec les espèces forestières méditerranéennes, sélection de ces isolats sur la base de critères physiologiques, production de jeunes plantules mycorhizées et caractérisation de ces mycorhizes, mesures des effets physiologiques de l'infection mycorhizienne en pépinière, mise en place et suivi de l'écologie et de l'écophysiologie de jeunes plants en reboisements expérimentaux.

summary Isozyme variation and somatic incompatibility were investigated in order to study intraspecific genetic variation and to identify genets in natural populations of the ectomycorrhizal fungus Suillus collinitus (Fr.) O. Kuntze, Forty-three isolates, obtained from basidiocarps collected in 11 forest sites under Pinus trees, were examined. Isozyme analysis indicated high intraspecific variation between isolates from the same location and from different locations. Phenetic analysis based on calculated dissimilarity values derived from isozyme banding patterns separated the isolates into two main groups (I and II) with 35% dissimilarity. A specific and highly active acid phosphatase isoform (ACP-2) was detected in most group II isolates. Dikaryotic isolates displaying isozyme similarity coefficient of 100 % were found to be somatically compatible and were considered to originate from the same genet. The same genet was never found at more than two forest sites. This study showed a high correlation between the results of electrophoretic isozyme analysis and those of somatic incompatibility reactions. The results were discussed in terms of population biology.

National audience

Summary In the mediterranean region, the strong edaphic, climatic and economic constraints lead to the increase of the transplantation crisis of young trees. The use of controlled mycorrhizal infection is one of the means open to reduce the effects of this crisis by improving the quality of the forest trees grown in nursery, and the reforestation. To achieve this objective, a research/development programme was started and preliminary results are presented: screening of mycorrhizal isolates using physiological criteria; controlled mycorrhizal infection including the study of enzymic polymorphism in mycorrhizae as a tool for characterization of these organs; measurement of the effects of mycorrhizal infection on the nutrition of trees in nursery; ecophysiological study of experimental wood lots.

International audience

International audience; communication orale

similar whole plant CO assimilation capacities, but root and total plant biomass were significantly higher in the R roseolus treatment. This difference could be due partly to greater carbon diversion by the fungal associate in the case of S collinitus 1. Mean water-use efficiency (WUE = CO assimilation rate/transpiration rate) of the inoculated seedlings (pooled mean value 7.29 mol kmolwas significantly (P < 0.05) higher than that of the controls (5.06 mol kmolThis is linked to the double tendency, neither being statistically significant, of the infected plants to exhibit higher CO assimilation rates and lower transpiration rates than the controls.

ResumeLes roles respectifs des partenaires de la symbiose ectomycorhizienne dans les metabolismes carbone, phosphate et azote des plantes mycorhizees sont etudies. Pour les echanges de carbone, la plante-hote est essentiellement la source et le mycosymbiote le puits. Cependant, les donnees quantitatives montrent que les mycorhizes peuvent ne pas etre le puits ultime des photosynthetats de cette plante. Pour les echanges de phosphore et d'azote, le phytosymbiote est le puits, le symbiote fongique la source.Les principales connaissances acquises au Laboratoire sur les metabolismes phosphate et azote du Pin maritime et des champignons Basidiomycetes ectomycorhiziens cultives separement sont presentees. A l'aide de ces donnees, le role possible du mycosymbiote dans la nutrition phosphatee et azotee de la plante-hote est propose.

After hydrolysis of chitin in 6 M HCl, the glucosamine produced was assayed colorimetrically. The pH of the hydrolysate was adjusted to a value close to three by addition of Na acetate; this procedure avoids the elimination of excess acid by evaporation under reduced pressure or freeze-drying. Under these conditions, the amount of glucosamine determined by the assay represented an average of 90% of the amount which would result from a total hydrolysis of the chitin. The method was used to assay the chitin in the mycelia of basidomycetes obtained in vitro. The measured amount of glucosamine was proportional to the mycelial biomass and allowed the estimation of fungal growth.

To estimate the intensity of mycorrhizal development of maritime pine (Pinus pinaster Soland. in Ait.) associated with Pisolithus tinctorius (Pers.) Coker et Couch., two methods were used: the assay of fungal chitin after acid or alkaline hydrolysis; the measure of absorption of fungus pigments extracted by means of acetone. The products of the hydrolysis of the chitin are assayed by a colorimetric method. The alkaline hydrolysis enables us to directly assay the fungal chitosan; after acid hydrolysis the tissues of pine produce some substances reacting colorimetrically and the absorption due to chitin is estimated from the total absorption of the hydrolysate. There are good correlations between these different types of determination themselves and between the determination and the counting of the mycorrhizae.

Comparison of phosphatase activities in ectomycorrhizal Homobasidiomycetes cultured in vitro . Phosphatase activities, measured on intact mycelia (accessible activities) or on mycelial homogenates (total activities), were compared in twelve ectomy corrhizal strains of Homobasidiomycetes (Hebeloma cylindrosporum, Laccaria laccata; Suillus bellini; S. bovinus; S. granulatus; S. luteus, Pisolithus arhizus). The effects of the following factors were examined: (i) two orthophosphate concentrations in the culture medium; (ii) two incubation substrates (sodium p-nitrophenylphosphate or sodium phytate). Phosphatase activities were highest when mycelial homogenates were incubated in the presence of p-nitrophenyl phosphate after culturing the mycelia on medium slightly deficient in orthophosphate, particularly in the case of one S. granulatus isolate.

ResumeLa localisation ultrastructurale des activites phosphatasiques acides est recherchee dans deux associations ectomycorhiziennes a Basidiomycetes, obtenues en conditions controlees.Dans le reseau de Hartig, les activites enzymatiques sont revelees sur le plasmalemme des cellules corticales vivantes et sur le plasmalemme des hyphes du champignon. Une faible activite diffuse est parfois observee dans le ciment interhyphal.Dans le manteau, ces activites sont mises en evidence le long du plasmalemme des hyphes et dans le ciment interhyphal. Les hyphes situees a la surface du manteau ou libres dans le milieu montrent une forte activite sur leur surface externe.Il n'a jamais ete observe d'activite phosphatasique acide dans les parois des cellules de l'hote ou des hyphes.Lorsque le champignon entre en degenerescence et quel que soit le niveau (manteau ou reseau de Hartig), il apparait une forte activite diffuse dans le le cytoplasme fongique.Les activites enzymatiques localisees sur les plasmalemmes de l'hot...

International audience; The influence of nitrogen source (nitrate, ammonium, nitrate and ammonium, glutamine) on growth of Cortinarius orellanus (isolate L6) and on accumulation of nitrogen and phosphorus in the mycelium was studied in vitro. Growth was poorest on nitrate which showed no significant accumulation, as in other Homobasidiomycetes previously studied. Soluble organic nitrogen and amine nitrogen accumulated in greater quantities (μmol N per mycelium) and concentrations (μmol N g−1d.w.) on nitrate medium. The relative proportions of insoluble nitrogen with respect to total nitrogen reached 75 and 40% on ammoniacal and nitric media, respectively. This results from those obtained in other Homobasidiomycetes and in most of the cultivated Phanerogams. This could reflect differences in ways of assimilating ammonium in vascular plants and indicates the role of ammonium in the enzymatic mechanisms that regulate amino-acid synthesis. The mean concentrations of total phosphorus varied from 0.8 to 0.9% of the dry weight of the mycelium.

International audience; An attempt was made to isolate the mycelium of Cortinarius orellanus and to look for orellanine in it, the structure of this molecule being 3,3′,4,4′-tetrahydroxy-2,2′-bipyridyl-1,1′-dioxide. A mycelial isolate of C. orellanus was obtained for the first time from an agar medium similar in composition to Pachlewski and Oddoux media. The identity of the cultures was confirmed by the chemical characterization of orellanine by tlc on cellulose and photodecomposition under uv light. The orellanine content from the cultured mycelium was weaker than those from the carpophore. This result was compared with those obtained by other authors for the genus Amanita and Gyromitra.

The orthophosphate and calcium influence on growth and ionic accumulation was studied in several ectomycorrhizal fungi (Pisolithus tinctorius included) grown in vitro. The "optimal" growth was obtained with [Formula: see text] concentrations much lower than those of usual media: it may be represented by an exponential function, the parameters ("maximal" growth and "concentration of half-maximal growth") of which were calculated. For low phosphate and calcium concentrations in the medium the dry matter mass of the mycelium and their content of the two elements increased simultaneously. For high concentrations, an accumulation independant of growth was observed in the thalli. When the P. tinctorius mycelium accumulated phosphate and calcium in relatively large amounts, these accumulations seemed to be not correlated. Rather, the correlation between the accumulation of total phosphorus and that of potassium was significant. The ratio of acid-soluble P to total P decreased in the mycelium when the orthophosphate concentration increased in the medium.

Après avoir rappelé la structure des hyphes mycéliens, les auteurs mettent l’accent sur les phénomènes d’exsorption (acidification) et d’accumulation des éléments minéraux par les champignons. A partir d’études expérimentales, ils montrent en particulier la possibilité de formation de carbonate de calcium sur les parois des filaments mycéliens. Parallèlement à ces études expérimentales, l’analyse micro-structurale d’échantillons naturels montre l’abondance de ces concentrations minérales dans les sols calcaires et fissures de roches., The structure and function of fungal hyphae is recalled with particular reference to exsorption (acidification) and accumulation of mineral elements. In laboratory experiments, the authors demonstrated the precipitation of calcium carbonate on the outer walls of fungal hyphae. Experiments showed that these and other biochemical transformations could take place very rapidly. In parallel with this experimental study, the microstructure of calcareous soils and rocks has been examined. The role of fungal hyphae in the formation of particular transformations has been clearly shown.

A partir de l’étude des microstructures du sol en place, à l’interface sol-système mycélien, les auteurs mettent en évidence la présence de concentrations calcaires à l’intérieur des hyphes de Basidiomycètes. Ces concentrations minérales s’identifient aux aiguilles de calcite, fréquemment observées dans les sols. L’étude de ces structures minérales très fragiles, rappelle la nécessité d’utiliser des techniques d’observation non destructives (loupe binoculaire) avant d’aborder toutes autres méthodes d’analyses microscopiques., Study of soil microstructure at the soil/mycelium interface has shown that calcite accumulations form within the hyphae of Basidiomycetes. These mineral concentrations are identical with the calcite needles which are frequently observed in soil. Non-destructive techniques (binocular microscope) are required to study these very fragile biological and mineral structures before any other microscopic or ultramicroscopic technique is applied.