Des champignons auxiliaires du sylviculteur

National audienceLes racines des arbres forestiers remplissent leurs fonctions d’absorption de l’eau et des éléments nutritifs du sol en association symbiotique obligatoire avec une grande diversité de champignons. La sylviculture met déjà ces connaissances en pratique et les progrès récents de la recherche dans ce vaste domaine des interactions plante/microorganisme ouvrent de nouvelles perspectives d’application à la gestion durable et à la protection des forêts

Differential ability of ectomycorrhizas to survive drying

International audienceTo test the hypothesis that, depending on the fungal symbiont, ectomycorrhizas are differentially affected by severe drought stress, we developed a simple method to quantify the loss of vitality of excised ectomycorrhizal tips subjected to drying under controlled conditions. The method uses 96-well microtitration plates with one single ectomycorrhizal tip per well, and is based on measuring the loss of volume and the loss of electrolytes before and after the imposed stress. This approach very significantly discriminated the two ectomycorrhizal morphotypes formed with beech (Fagus silvatica) by Lactarius subdulcis and Cenococcum geophilum, which confirmed the ability of the latter fungal species to protect roots against desiccation already suggested by previous works. The new method should contribute to the present effort in deciphering the functional diversity of complex ectomycorrhizal communities

Improving the growth of oak plantations using controlled mycorrhizrtion: Results from 12 experiments in north-erstern France

The growth of bare-root oak seedlings (Quercus petraea and Quercus robur), mycorrhized with Thelephora terrestris or four other fungi by means of nursery inoculation, was compared after outplanting in 12 clear-cut forest sites in North-Eastern France. Some strains of Paxillus involutus and Laccaria bicolor proved to be good candidates for routine inoculation in oak nurseries, compared to Thelephora terrestris, which is the dominant fungal symbiont, associated with commercial oak planting stock in France. They provide significant extra growth, resulting in reduced competition from the vegetation. However, the effect is nil if seedlings are planted in a grassy meadow.La croissance de semis de Chêne (Quercus petraea et Quercus robur) à racines nues, mycorhizés par Thelephora terrestris ou quatre autres champignons par inoculation en pépinière, a été comparée après plantation dans 12 parcelles forestières coupées à blanc dans le Nord-Est de la France. Certaines souches de Paxillus involutus et de Laccaria bicolor se sont révélées être de bonnes candidates pour l’inoculation en routine des pépinières de Chêne, par rapport à Thelephora terrestris qui est le principal symbionte fongique associé aux plants commerciaux de Chêne en France. Elles procurent un gain de croissance significatif, avec comme résultat une moindre compétition de la part de la végétation. Cependant, l’effet est nul si les semis sont plantés dans une prairie de graminées

Amélioration de la croissance des plantations de chêne par mycorhization contrôlée : bilan de 12 essais dans le Nord-est de la France

National audienceLa croissance de semis de Chêne (Quercus petraea et Quercus robur) à racines nues, mycorhizés par Thelephora terrestris ou quatre autres champignons par inoculation en pépinière, a été comparée après plantation dans 12 parcelles forestières coupées à blanc dans le Nord-Est de la France. Certaines souches de Paxillus involutus et de Laccaria bicolor se sont révélées être de bonnes candidates pour l’inoculation en routine des pépinières de Chêne, par rapport à Thelephora terrestris qui est le principal symbionte fongique associé aux plants commerciaux de Chêne en France. Elles procurent un gain de croissance significatif, avec comme résultat une moindre compétition de la part de la végétation. Cependant, l’effet est nul si les semis sont plantés dans une prairie de graminées

Effect of controlled mycorrhization on growth, natural pruning and epicormic shoots of pedunculate oak 16 years after planting

Les arbres d'une plantation de Chêne pédonculé (Quercus robur L.) de 16 ans dans le Nord-Est de la France, réalisée avec des plants mycorhizés ou non par le champignon Paxillus involutus, ont été étudiés du point de vue de la croissance, de l'élagage naturel et des gourmands. Les résultats montrent que la stimulation de croissance initiale se traduit encore par un effet significatif sur la hauteur totale, mais que le traitement fongique n'a plus d'effet sur la hauteur ou le diamètre de la première branche vivante. Les arbres initialement mycorhizés par Paxillus involutus tendent à avoir plus de gourmands, avec une fréquence plus élevée de gourmands groupés. Cependant, la plupart de ces gourmands sont petits et de durée de vie très limitée, et la conclusion générale est que le gain de croissance procuré par la mycorhization contrôlée n'est en rien compromis par d'éventuels effets secondaires pouvant déprécier la qualité des tiges

Effect of poplar genotypes on mycorrhizal infection and secreted enzyme activities in mycorrhizal and non-mycorrhizal roots

International audienceThe impact of ectomycorrhiza formation on the secretion of exoenzymes by the host plant and the symbiont is unknown. Thirty-eight F-1 individuals from an interspecific Populus deltoides (Bartr.)xPopulus trichocarpa (Torr. & A. Gray) controlled cross were inoculated with the ectomycorrhizal fungus Laccaria bicolor. The colonization of poplar roots by L. bicolor dramatically modified their ability to secrete enzymes involved in organic matter breakdown or organic phosphorus mobilization, such as N-acetylglucosaminidase, beta-glucuronidase, cellobiohydrolase, beta-glucosidase, beta-xylosidase, laccase, and acid phosphatase. The expression of genes coding for laccase, N-acetylglucosaminidase, and acid phosphatase was studied in mycorrhizal and non-mycorrhizal root tips. Depending on the genes, their expression was regulated upon symbiosis development. Moreover, it appears that poplar laccases or phosphatases contribute poorly to ectomycorrhiza metabolic activity. Enzymes secreted by poplar roots were added to or substituted by enzymes secreted by L. bicolor. The enzymatic activities expressed in mycorrhizal roots differed significantly between the two parents, while it did not differ in non-mycorrhizal roots. Significant differences were found between poplar genotypes for all enzymatic activities measured on ectomycorrhizas except for laccases activity. In contrast, no significant differences were found between poplar genotypes for enzymatic activities of non-mycorrhizal root tips except for acid phosphatase activity. The level of enzymes secreted by the ectomycorrhizal root tips is under the genetic control of the host. Moreover, poplar heterosis was expressed through the enzymatic activities of the fungal partner

A Transcriptomic Atlas of the Ectomycorrhizal Fungus Laccaria bicolor

Trees are able to colonize, establish and survive in a wide range of soils through associations with ectomycorrhizal (EcM) fungi. Proper functioning of EcM fungi implies the differentiation of structures within the fungal colony. A symbiotic structure is dedicated to nutrient exchange and the extramatricular mycelium explores soil for nutrients. Eventually, basidiocarps develop to assure last stages of sexual reproduction. The aim of this study is to understand how an EcM fungus uses its gene set to support functional differentiation and development of specialized morphological structures. We examined the transcriptomes of Laccaria bicolor under a series of experimental setups, including the growth with Populus tremula x alba at different developmental stages, basidiocarps and free-living mycelium, under various conditions of N, P and C supply. In particular, N supply induced global transcriptional changes, whereas responses to P supply seemed to be independent from it. Symbiosis development with poplar is characterized by transcriptional waves. Basidiocarp development shares transcriptional signatures with other basidiomycetes. Overlaps in transcriptional responses of L. bicolor hyphae to a host plant and N/C supply next to co-regulation of genes in basidiocarps and mature mycorrhiza were detected. Few genes are induced in a single condition only, but functional and morphological differentiation rather involves fine tuning of larger gene sets. Overall, this transcriptomic atlas builds a reference to study the function and stability of EcM symbiosis in distinct conditions using L. bicolor as a model and indicates both similarities and differences with other ectomycorrhizal fungi, allowing researchers to distinguish conserved processes such as basidiocarp development from nutrient homeostasis