PHYSIOLOGY AND ECOLOGY OF ORCHID MYCORRHIZAL FUNGI WITH REFERENCE TO SEEDLING NUTRITION

Abstract

SummaryOrchid mycorrhizal fungi have been assumed to supply carbohydrates to the orchid seedlings with which they are associated. To do this they must be able to utilize a regular source of carbohydrate in the soil, and also to translocate soluble compounds to the orchids. Mycorrhizal Rhizoctonia spp. were shown to decompose filter paper cellulose in pure culture. Secondly, R. repens and R. solani, isolated from Dactylorchis purpurella, were able to compete with other soil micro‐organisms in the exploitation of cellulose buried in unsterilized soil. Rhizoctonia repens was found capable of translocating 32P and‘14C labelled compounds in an already established mycelium. Radioactivity could also be detected in infected seedlings if tracers were fed to the infecting hyphae some distance from the seedlings. This translocation from fungus to seedlings resulted in greater growth of the seedlings if cellulose was available to the infecting fungus than if no carbohydrates were supplied to either fungus or seedlings.