A GNOTOBIOTIC CULTURE SYSTEM WITH OAK MICROCUTTINGS TO STUDY SPECIFICEFFECTS OF MYCOBIONTS ON PLANT MORPHOLOGY BEFORE, AND IN THE EARLY PHASE OF, ECTOMYCORRHIZA FORMATION BY PAXILLUS-INVOLUTUS AND PILODERMA-CROCEUM

Homogeneously developed oak (Quercus robur L.) microcuttings were chal lenged in a Petri-dish system with the mycobionts Piloderma croceum J. Erikss. & Hjortst. and Paxillus involutus (Batsch) Fr. Non-destructive observations over 10 wk followed by d. wt measurements at the end of the assays served to precisely characterize root and shoot development , dynamics of mycorrhizal colonization and morphological ratio. In the system, plant development, and especially root morphogenesis, had mor e similarities to those of stump cuttings or of older seedlings than t o those of 3-month-old seedlings. Whereas Paxillus involutus displayed early mycorrhizal colonization and had no significant morphological e ffects on the host Piloderma croceum modified markedly the entire plan t development before a delayed mycorrhiza formation. The latter mycobi ont stimulated elongation and production of the lateral root system an d also increased the leaf surface. However, no corresponding weight in creases were noted, which was reflected by significant increase of bot h specific root length and specific leaf area. These differential effe cts are discussed in relation to data concerning carbon requirement an d auxin production of the mycobionts. The developed system was shown t o be highly suitable for comparative studies with diverse mycobionts o n recognition and physiological balance between partners before, and i n the early stage of, formation of mycorrhizas.