UTILIZATION OF CELL-WALL RELATED CARBOHYDRATES BY ERICOID MYCORRHIZALENDOPHYTES

The ability of some strains of ericoid mycorrhizal fungi to utilize ce ll wall related mono-, di- and complex polysaccharides as sole carbon and energy source was investigated. Xylose, galactose, laminarin, tylo se and carboxymethyl cellulose (CMC) supported the growth of several e ndophytes, such as Hymenoscyphus ericae (strain Read and strain A), Du clos XV, PS I, and II. By contrast, PS IV showed good growth only with laminarin and tylose. PS IV needed supplemented medium with malt or p eptone extract dialysates in combination with surfactants (tween 20, t ween 60 or triton-X-100) to degrade CMC. Increased growth often led to the production of loose, hyaline mycelial wefts. Commercial cellulosi c materials (filter paper, scottex and microcrystalline cotton) also s upported growth in H. ericae strain Read and PS TV as well as steriliz ed roots of Calluna and clover. The degradation of beta 1,4- and beta 1,3-glucans was tested in two fungal strains (H. ericae strain Read an d PS IV) by enzymatic assays that revealed the corresponding glucanase activities. Glucanase activities were detected when the fungi grew on CMC medium and on the sterilised root segments. The experiments sugge st the involvement of hydrolytic enzymes in the degradation of structu ral organic molecules present in the soil matrices and/or in the host cell walls: they could be produced by the ericoid mycorrhizal fungi bo th during the saprotrophic and symbiotic phase.