Synthesis and ultrastructural observation of arbutoid mycorrhizae of black truffles (Tuber melanosporum and T. aestivum)

Arbutus unedo (the strawberry tree) is a Mediterranean shrub which forms arbutoid mycorrhizae with a variety of Asco- and Basidiomycetes. After the discovery of the mycorrhizal symbiosis between A. unedo and Tuber borchii, in this study, arbutoid mycorrhizae were synthetized in greenhouse with Tuber aestivum and Tuber melanosporum. Six months after inoculation, both species colonized the roots of all inoculated A. unedo seedlings, but mature mycorrhizae were only observed after 12 months. Ultrastructure analysis of Tuber arbutoid mycorrhizae was described for the first time, showing, as observed in typical endosymbiosis, a rearrangement of host cells and the creation of an interface compartment with both truffle species. Immunolabelling experiments suggested that pectins are not present in the interface matrix surrounding the intracellular hyphae. Thus, the ability to establish symbiosis with A. unedo seems to be a common feature in the genus Tuber, opening up the possibility to use this plant for mycorrhization with valuable truffles. This could represent an important economic opportunity in Mediterranean areas by combining the production of truffles, edible fruits and valued honey.

Visualization of mycorrhizal fungal structures in resin embedded tissues with xanthene dyes using laser scanning confocal microscopy

The xanthene dyes sulforhordamine G, phloxine B, rose Bengal, and 4,5,6,7-tetrachloroflorescein were used as fluorochromes for laser scanning confocal microscopy of LR-White resin-embedded mycorrhizae. Sulforhodamine G was the most effective dye, giving an even staining of cell components throughout the material, with minimal background fluorescence of LR-White resin. Confocal microscopy of stained blocks of tissue on a slide, viewed without the use of a coverslip, revealed the three-dimensional nature of various mycorrhizal structures; these structures included arbuscules, vesicles, and coiled hyphae in arbuscular mycorrhizae; coiled hyphae in orchid mycorrhizae; mantle and Hartig net hyphae in ectomycorrhizae; and intracellular hyphae in arbutoid mycorrhizae. Sections mounted on slides viewed with confocal microscopy provided exceptional clarity of fungal form and cytoplasmic contents and showed the relationship to the plant cells, also with negligible background fluorescence. Mounting and staining blocks of resin-embedded material provided a fast and effective technique for the visualization of a variety of plant and fungal tissues. Stain penetration in whole-mounted samples was sufficient to reconstruct clear three-dimensional images using confocal microscopy.Key words: mycorrhizae, xanthene dyes, confocal microscopy, resin embedding.

Diversity and abundance of ericoid mycorrhizal fungi of Gaultheria shallon on forest clearcuts

Roots of salal (Gaultheria shallon Pursh) collected from forest clearcuts were examined by light and scanning electron microscopy, and the ericoid mycorrhizal fungi were isolated and identified. Heavy colonization of typical ericoid mycorrhizae was present in and restricted to the first of the two layers of root cortical cells. Neither ectomycorrhizae nor arbutoid mycorrhizae were observed. In the field, over 85% of the roots and 90% of the cortical cells within colonized roots were colonized. One hundred and seventy-five of the 278 fungal isolates from salal roots formed ericoid mycorrhizae with salal in the laboratory, and these isolates were grouped into four species based on spore formation and cultural characteristics: Oidiodendron griseum Robak, Acremonium strictwn W. Gams, and two unidentified, nonsporulating fungal species. The association in the laboratory between A. strictum and salal was atypical in that the fungus improved the growth of salal seedlings but was slow to colonize roots and occasionally grew and even sporulated on the shoots. No differences in percent colonization or diversity of ericoid mycorrhizal fungi were found in salal growing on clearcuts from two different forest types. Keywords: Gaultheria shallon, Oidiodendron griseum, Acremonium strictum, ericoid mycorrhizal fungi.

Ultrastructural aspects of Pyrola mycorrhizae

The mycorrhizae of six species of Pyrola were examined with light and electron microscopes. The hyphae on the root surface varied from a loose weft to an abundant mass with numerous strands, but no organized sheath was observed. Infection began with the formation of a Hartig net several millimetres behind the root tip. Hyphae from this net subsequently grew into each epidermal cell, forming masses of intracellular hyphae. These hyphae were surrounded by the host plasmalemma and a matrix material, presumably of host origin. During the stage of mature infection the host cytoplasm was finely granular and filled with organelles. The host vacuoles often had tanninlike deposits along their tonoplasts. Senescence of the symbiosis began with the gradual degeneration of the host cytoplasm, which became dark and vesiculated with loss of its organelles. The fungal hyphae and matrix material appeared essentially unchanged at this stage but eventually degenerated and collapsed. The fungal partners were normally basidiomycetes with dolipore septa, but one ascomycetous infection (distinguished by simple septa and Woronin bodies) was found to have a similar mycorrhizal organization. It differed in having an intermittent Hartig net. The presence of both the Hartig net and intracellular hyphae indicates that these are arbutoid mycorrhizae.

The mycorrhizal status of boreal plants: additional species from northeastern Ontario

Thirty-one species of vascular plants commonly occurring in the Boreal Forest Region of northeastern Ontario were examined for the presence of mycorrhizae. Two species were ectomycorrhizal, 3 both ecto- and endo-mycorrhizal, and 15 endomycorrhizal. Two species of Ericaceae had ericoid mycorrhizae and one had both ericoid and arbutoid mycorrhizae. Eight species, unexpectedly including three species of Rosaceae and two of Saxifragaceae, completely lacked mycorrhizae. The significance of the findings concerning the Betulaceae, Fraxinus, the Ericaceae, Rosaceae, and Saxifragaceae are discussed, as is occurrence of Cenococcum-type infections among the species.

The mycorrhizal status of boreal plants: species from northeastern Ontario

Twenty-nine species of vascular plants commonly occurring in the Boreal Forest Region of northeastern Ontario were examined for the presence of mycorrhizae. Four species were ectomycontiizal, 4 both endo- and ecto-mycorrhizal, and 15 endomycorrhizal. Among the Ericaceae, one had arbutoid mycorrhizae and five ericoid mycorrhizae. The distribution of Cenococcum geophilum among the ectomycorrhizal and arbutoid plants is compared. Selected findings are discussed in relation to reports in the literature.

Occurrence of mycorrhizae on ericaceous and pyrolaceous plants in northern California

Four hundred and eighty plants in northern California from 27 taxa in the Ericaceae and 5 in the Pyrolaceae were surveyed for presence of ectomycorrhizae, arbutoid, or ericoid mycorrhizae between September 1977 and April 1978. Of these, 337 in the Ericaceae and 8 in the Pyrolaceae had one or more types of mycorrhizae.At least 88% of the plants of larger shrubs or trees (Arbutus menziesii or Arctostaphylos spp.) were mycorrhizal in various locations in northern California. Of the plants in the remaining twenty-two taxa that were mycorrhizal, 67–100% had ectomycorrhizae or arbutoid mycorrhizae. Twenty-three taxa of ericaceous or pyrolaceous plants in the genera Cassiope, Gaultheria, Kalmia, Ledum, Leucothoe, Phyllodoce, Rhododendron, Vaccinium, Pyrola, and Chimaphila were also mycorrhizal. The type and abundance of mycorrhizae appear to depend on as yet undefined ecological factors.Ectomycorrhizae (including the Cenococcum type) or ericoid mycorrhizae are reported for the first time in Arbutus, most Arctostaphylos spp., Gaultheria shallon, Kalmia polifolia, Ledum glandulosum var. columbianum, Leucothoe davisiae, Rhododendron macrophyllum, Vaccinium arbuscula, V. ovatum, V. scoparium, Chimaphila menziesii, and Pyrola picta f. picta.