Development and function of Pisolithus and Scleroderma ectomycorrhizas formed in vivo with Allocasuarina, Casuarina and Eucalyptus.
The effect of inoculating seedlings of E. grandis, A. littoralis and C. equisetifolia with 2 isolates of Pisolithus and 2 isolates of Scleroderma from under eucalypts was examined in a glasshouse trial. Ectomycorrhizas formed extensively on E. grandis (23-46% fine roots ectomycorrhizal) and A. littoralis (18-51% fine roots ectomycorrhizal). On C. equisetifolia, the fungi were either unable to colonize the rhizosphere (one isolate of Pisolithus), or sheathed roots, resembling ectomycorrhizas, formed on 1-2% of the fine roots. Colonization of roots by one isolate of Scleroderma resulted in the death of seedlings of C. equisetifolia. Inoculation with fungi increased shoot DW by up to a factor of 32 (E. grandis), 4 (A. littoralis) and 3 (C. equisetifolia). Ectomycorrhizas formed in associations with E. grandis and A. littoralis had fully differentiated mantles and Hartig nets in which the host and fungal cells were linked by an extensive fibrillar matrix. Sheathed roots in C. equisetifolia lacked a Hartig net, and the epidermis showed a hypersensitive reaction resulting in wall thickening and cell death. The sheaths are described as mantles since the density and arrangements of the hyphae in the sheaths was similar to that in mantles of the eucalypt ectomycorrhizas. The intercellular carbohydrate matrix was not produced in the C. equisetifolia mantle in association with Pisolithus, hence the mantle was not cemented to the root. These structures differed from poorly compatible associations described previously for Pisolithus and E. grandis. The anatomical data indicated that ectomycorrhizal assessment based on surface morphological features may be misleading in ecological studies because compatible and incompatible associations may not be distinguishable.