EFFECTS OF MYCORRHIZAL FUNGI ON IN-VITRO NITROGEN RESPONSE OF SOME DUTCH INDIGENOUS ORCHID SPECIES

The effect of mycorrhizal infection on the response to mineral nitrogen was studied in Orchis morio L., Dactylorhiza praetermissa (Druce) Soo var. junialis (Vermin.) Sengh., Dactylorhiza majalis (Reichb.) Hunt & Summerh., and Dactylorhiza incarnara (L.) Soo, using two strains of Ceratorhiza sp. and two of Epulorhiza repens (Bernard) Moore as mycorrhizal symbionts. Both types of endophyte appeared to be able to stimulate orchid growth at relatively low nitrogen availability in the culture medium. The Ceratorhiza strains decreased nitrogen tolerance of associated orchid protocorms and had pronounced negative effects on the growth and survival of D. majalis and D. incarnata at high concentrations of ammonium nitrate. Such effects did not occur in symbioses involving the Epulorhiza strains. Within orchid species, differences were observed in the extent to which fungal strains stimulated growth. The Ceratorhiza isolates were incompatible with O. morio while the Epulorhiza strains were generally less efficient for Dactylorhiza spp.