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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.

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.

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International audience

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.

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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.

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.