Ericoid mycorrhizal fungi are common root associates of a Mediterranean ectomycorrhizal plant (Quercus ilex)

Mycorrhiza samples of neighbouring Quercus ilex and Erica arborea plants co llected in a post-cutting habitat were processed to see whether plants diff ering in mycorrhizal status harbour the same root endophytes. Three experim ents were performed in parallel: (i) isolation, identification and molecula r characterization of fungi from surface-sterilized roots of both plant spe cies; (ii) re-inoculation of fungal isolates on axenic E. arborea and Q. il ex seedlings; (iii) direct inoculation of field-collected Q. ilex ectomycor rhizas onto E. arborea seedlings. About 70 and 150 fungal isolates were obt ained from roots of Q. ilex and E. arborea, respectively. Among them, Oidio dendron species and five cultural morphotypes of sterile isolates formed ty pical ericoid mycorrhizas on E. arborea in vitro. Fungi with such mycorrhiz al ability were derived from both host plants. Isolates belonging to one of these morphotypes (sd9) also exhibited an unusual pattern of colonization, with an additional extracellular hyphal net. Ericoid mycorrhizas were also readily obtained by direct inoculation of E. arborea seedlings with Q. ile x ectomycorrhizal tips. Polymerase chain-restriction fragment length polymo rphism and random amplified polymorphic DNA analyses of the shared sterile morphotypes demonstrate, in the case of sd9, the occurrence of the same gen et on the two host plants. These results indicate that ericoid mycorrhizal fungi associate with ectomycorrhizal roots, and the ecological significance of this finding is discussed.