Ultrastructure of hyphal walls and septa of Cronartium ribicola on tissue cultures of Pinus monticola

Abstract

Colonies of the rust fungus Cronartium ribicola J. C. Fischer were grown axenically and then transferred so that they lay immediately next to callus cultures of the pine host (Pinus monticola Dougl.). Twelve days after the establishment of this association samples of the fungal mycelium taken 2 mm away from the pine callus and at the host–parasite interface were fixed for electron microscopy. Differences were found in the appearance and thickness of the lateral walls and extracellular coatings depending on the proximity of the fungus to the host–parasite interface. Septa were intermediate in structure between the Ascomycete and dolipore types. The origin of the extracellular sheath is discussed.