J. André Fortin

Mitochondrial DNA polymorphisms in Laccaria bicolor, L. laccata, L. proxima and L. amethystina

The mitochondrial DNA (mtDNA) from 25 Laccaria bicolor , 8 L. laccata , 3 L. proxima and 2 L. amethystina isolates was examinated by restriction fragment length polymorphism (RFLP) analysis. Whole-cell DNA from Laccaria isolates was digested with Bam HI, Bgl II and Hind III and probed in Southern hybridizations with cloned mitochondrial fragments from L. bicolor . Analysis of restriction fragment length polymorphisms indicated that mtDNA fragment patterns can be used as additional taxonomic characters for delimiting Laccaria spp. However, intraspecific variation was very high with almost no similarity observed among the four biological species of L. laccata or between the 2 isolates of L. amethystina . A high level of variability was also detected within L. bicolor and several subgroups, possibly biological species, were discernible among the L. bicolor isolates examined. No major discrepancies were observed between the trends indicated by RFLP results on mtDNA and those on nuclear ribosomal DNA. As most of the Laccaria isolates had unique overall mitochondrial pattern, this variability could be used for isolate typing.

Differential development of root colonization among four closely related genotypes of ectomycorrhizal Laccaria bicolor

Time course experiments were used to study the colonization of Pinus banksiana roots by 4 variants of Laccaria bicolor (d1 and d2 being dikaryons made by crossing the 2 sib-monokaryons, m4 and m10, on two separate occasions). Hyphal-root contact was first observed 4 or 5 d after inoculation. In the 2 d time required for the completion of the thick mantle of d1 on long roots, the Hartig net reached the endodermis and separated cortical cells widely. Mantle development on short roots by dl was also rapid but Hartig net penetration into the inner root cortex was slower with narrow separations of cortical cells. Despite slower development rates in comparison to that of dl, Hartig nets formed by d2 and m10 also reached the endodermis and those in short roots often resulted in greater separation of cortical cells. Mantles formed by d2 and m10 were however thin. No mantle was formed by m4 whereas Hartig net development was infrequent and weak. The substantial phenotypic differences among these closely related fungal genotypes warrant further investigations.

Methods for synthesizing ectomycorrhizas and their effect on mycorrhizal development

SummaryThe different methods used for synthesizing ectomycorrhizae since Melins first experiments were reviewed and evaluated. A non-aseptic growth pouch method was proposed that allowed for the formation of ectomycorrhizae on several species of Pinaceae and of actinorhizal and non-actinorhizal angiosperms including woody cuttings. More than 30 fungal species thus tested formed ectomycorrhizae. In most cases full ectomycorrhiza formation required 3–10 days after inoculation. The method allowed for chronosequential destructive (fixation) and non-destructive (photography) observations. It was particularly useful for the description of extramatrical phase development including hyphal strands, sclerotia and fruit body primordia formation.

Morchella tomentosa: a unique belowground structure and a new clade of morels

Mechanisms involved in post-fire morel fructification remain unclear. A new undescribed belowground vegetative structure of Morchella tomentosa in a burned boreal forest was investigated north of Fairbanks, Alaska. The name “radiscisclerotium” is proposed to define this peculiar and elaborate below-ground vegetative structure of M. tomentosa. Bayesian and maximum parsimony analyses based on ITS rRNA regions and nLSU gene strongly supported a new clade composed of M. tomentosa within the genus Morchella.

Igneous phosphate rock solubilization by biofilm-forming mycorrhizobacteria and hyphobacteria associated with Rhizoglomus irregulare DAOM 197198.

Biofilm formation on abiotic and biotic surfaces was studied with two hyphobacteria, strongly attached to the surface of the arbuscular mycorrhizal fungus (AMF) Rhizoglomus irregulare (Ri) DAOM 197198 and two mycorrhizobacteria, loosely attached to the roots of different mycorrhizal plants. When the sparingly soluble igneous phosphate rock (PR) from Quebec, or when the chemical hydroxyapatite were used as sole phosphorus (P) source, hyphobacteria Rhizobium miluonense Rm3 and Burkholderia anthina Ba8 produced significantly more biofilms than mycorrhizobacteria Rahnella sp. Rs11 and Burkholderiaphenazinium Bph12, as indicated by the crystal violet assay or by quantifying biofilm exopolysaccharides. As previously observed with planktonic bacteria, biofilms mobilized P by lowering the pH and releasing gluconic acid. The high efficiency of P mobilization by the hyphobacteria Ba8 was linked to the presence of more viable cells in its biofilm as revealed by the hydrolysis of fluorescein diacetate. Scanning electron microscopy micrographs showed a high adherence of the best P-solubilizer hyphobacteria Ba8 on the surface of Quebec PR. Hydroxyapatite porous structure did not allow a good adherence of Ba8. Ba8 formed an important biofilm on the hyphae of Ri DAOM 197198 with low reactive Quebec PR while no biofilm was observed with the high reactive hydroxyapatite. Results confirm the possible presence of specificity between the Ri DAOM 197198 and the hyphobacteria and suggest that the interaction would be regulated by the availability of P.

Presence of a linear plasmid-like DNA molecule in the fungal pathogen Ceratocystis fimbriata Ell. & Halst.

SummaryA plasmid-like molecule was detected in a strain of the ascomycete Ceratocystis fimbriata Ell. & Halst., a pathogenic fungus of Populus spp. The DNA replicon, designated pFQ501, was found to have a linear structure with a length of 6.0 kb (3.9 × 106 daltons) and a density of 1.685 g/cc. This molecule was found to be associated with the mitochondria and was isolated from the gel; its restriction map was deduced from single and double digestions.

Diarimella laurentidae anam.: sp.nov. from Quebec

Diarimella laurentidae, a new species occurring on dead bark and decorticated twigs of American beech (Fagus grandifolia Ehrh.), is reported from the Muirs Wood ecological reserve, located in the centre of the Haut-Saint-Laurent region in the province of Quebec. Diarimella laurentidae is characterized by stromatic, pulvinate, black, setose fructifications composed of a basal stroma of textura angularis, a brown peripheral wall of textura porrecta, conidiomatal setae of two types, and unicellular multisetulate conidia. Its relationships with described Diarimella species is discussed. This is the first report of a species of Diarimella from North America.Key words: Diarimella laurentidae, new fungus species, coelomycete, Fagus grandifolia.

Colonization of Pinus banksiana roots by Laccaria bicolor variants: structural characterization

Abstract Under aseptic conditions, several sib-monokaryotic and dikaryotic strains of ectomycorrhizal Laccaria bicolor were individually introduced to roots of Pinus banksiana seedlings. Fungal-root interactions were subsequently examined using microscopic techniques. We found that the colonization of short roots varied among the strains with respect to the extent of fungal growth on root surfaces and the extent of fungal penetration into roots.