DEVELOPMENT AND FUNCTION OF PISOLITHUS AND SCLERODERMA ECTOMYCORRHIZAS FORMED IN-VIVO WITH ALLOCASUARINA, CASUARINA AND EUCALYPTUS

The effect of inoculating seedlings of Eucalyptus grandis, Allocasuari na littoralis and Casuarina equisetifolia with two isolates of Pisolit hus and two isolates of Scleroderma from under eucalypts was examined in a glasshouse trial. Ectomycorrhizas formed extensively on Eucalyptu s (23-46% fine roots ectomycorrhizal) and Allocasuarina (18-51% fine r oots ectomycorrhizal). On Casuarina, the fungi were either unable to c olonize the rhizosphere (one isolate of Pisolithus), or sheathed roots , resembling ectomycorrhizas, formed on 1-2% of the fine roots. Coloni zation of roots by one isolate of Scleroderma resulted in the death of Casuarina seedlings. Inoculation with fungi increased shoot dry weigh t by up to a factor of 32 (Eucalyptus), 4 (Allocasuarina) and 3 (Casua rina). Ectomycorrhizas formed in associations with Eucalyptus and Allo casuarina had fully differentiated mantles and Hartig nets in which th e host and fungal cells were linked by an extensive fibrillar matrix. Sheathed roots in Casuarina lacked a Hartig net, and the epidermis sho wed a hypersensitive reaction resulting in wall thickening and cell de ath. The sheaths are described as mantles since the density and arrang ement of the hyphae in the sheaths was similar to that in mantles of t he eucalypt ectomycorrhizas. The intercellular carbohydrate matrix was not produced in the Casuarina mantle in association with Pisolithus, hence the mantle was not cemented to the root. These structures differ from poorly compatible associations described previously for Pisolith us and Eucalyptus. The anatomical data indicate that ectomycorrhizal a ssessment based on surface morphological features may be misleading in ecological studies because compatible and incompatible associations m ay not be distinguishable.