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The role of root-associated fungi in the dominance of gaultheria shallon Xiao, Guoping


Field roots of salal (Gaultheria shallon Pursh) were examined by light and scanning electron microscopy. Salal formed typical ericoid mycorrhizae characterized by a weft of hyaline hyphae on the surface of the hair roots and crowded hyphal complexes inside the outer layer of cortical cells. Heavy colonization by ericoid mycorrhizal fungi was present in and restricted to the outer of the two layers of root cortical cells. In some cases, a mantle-like structure of hyphae but no Hartig net was observed on the surface of these roots. Neither ectonor arbutoid mycorrhizae were observed on salal roots collected in the field. Over 85% of the roots and 90% of the cortical cells within roots were colonized. Four species of root-associated fungi were isolated from field-collected salal roots. Three of them were proven to form ericoid mycorrhizae and one of them formed pseudomycorrhizae in axemc culture. This includes Oidiodendron griseum Robak, Acremonium strictum W. Gams and two nonsporulating unknown species, which were described in culture. Twelve known ericoid mycorrhizal fungi were tested for their ability to form mycorrhizae with salal in axenic culture. Five of the fungi developed typical ericoid mycorrhizae. These fungi are Hymenoscyphus ericae (Read) Korf & Keman, Oidiodendron flavum Szilvinyi, O. maius Barron, Pseudogymnoascus roseus Raillo, and Scytalidium vaccinhi Dalpe, Litten and Sigler. The ability of the four species of root-associated fungi isolated from salal field roots to use different forms of organic nitrogen was tested in pure culture or in association with salal. The organic forms of nitrogen applied were glutamine (an amino acid), glutathione (a peptide), and bovine serum albumin (BSA, a protein). The fungi tested were Oidiodendron griseum, Acremonium strictum, and two nonsporulating unknown fungi. Glutamine was used as readily as ammonium nitrogen by all four fungi and the plants of salal inoculated by those fungi. Oidiodendron griseum on glutathione and Acremonium strictum on BSA produced significantly higher yields in pure culture or in association with salal plants. The plants of salal inoculated by all four fungi had higher colonization rate on glutathione or BSA than on ammonium or glutamine. The colonization of salal roots by its root-associated fungi was reduced by application of available nitrogen and simple organic nitrogen, and favored by more complicated organic nitrogen. In vitro interactions between species of 4 root-associated fungi, Acremonium strictum, Oidiodendron griseum and 2 unknowns, isolated from field salal roots and 3 ectomycoffhizal fungi of western hemlock (Tsuga heterophylla (Raf.) Sarge.), Pisolithus tinctorius (Pers.) Coker & Couch, Rhizopogon semireticulatus Smith and Suillus lakei (Muff.) Smith & Thiers, were examined and characterized on buffered and unbuffered modified Melin Norkrans agar (MMN) at 25°C. Three interaction patterns were revealed, neutral intermingling, deadlock and inhibition. lithibition, in which the growth of one mycelium was reduced by the other, was the predominant outcome of the pairing of ectomycorrhizal fungi opposing the root-associated fungi of salal. All 3 ectomycorrhizal fungi were inhibited by rootassociated fungi of salal, but none of the four root-associated fungi was inhibited by any of the ectomycorrhizal fungi. Acremonium strictum was the most aggressive of the root-associated fungi of salal. It inhibited all 3 ectomycorrhizal fungi in 5 out of 6 interspecific pairings on both media. Oldiodendron griseum was the second in terms of aggressiveness to the ectomycorrhizal fungi. Suillus lakei and Rhizopogon semireticulatus were kept in check by 3 of the 4 rootassociated fungi on both media.

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