ELECTRON MICROSCOPY OF THE HOST-PARASITE RELATIONSHIPS IN STEM RUST OF WHEAT

Ehrlich , H. G., and Mary A. Ehrlich . (Duquesne U., Pittsburgh, Pa.) Electron microscopy of the host-parasite relationships in stem rust of wheat.—Amer. Jour. Bot. 50(2): 123–130. Illus. 1963.—A series of micrographs showing intercellular dikaryotic mycelium, haustorial mother cells, stages in haustorial formation, and haustoria within host cells are presented in the present report. Of special interest and potential significance in a study of obligate parasitism is an encapsulation ranging from 800 to 3400 A in thickness which surrounds the haustorium, but which is not present around the intercellular hyphae. The encapsulation completely encases the haustorium proper; it is bounded on the inside by the cell wall of the haustorium, and its thin membranous outer margin abuts directly on the protoplast of the host cell. The nature of the material composing the encapsulation is uncertain, but it appears to originate from the haustorial protoplast, and at least a portion of it may be fungal cytoplasm. This newly described structure represents the actual interface between the host and pathogen. Small vesicles which seem to originate from the outer margin of the encapsulation are sometimes found in the host cytoplasm surrounding apparently vigorous haustoria. The vesicles are bounded by a membrane and contain particulate material.