THE HAUSTORIUM OF ERYSIPHE CICHORACEARUM AND THE HOST–PARASITE INTERFACE ON HELIANTHUS ANNUUS

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Abstract
Electron microscopy showed that the haustoria of Erysiphe cichoracearum which were randomly scattered in the epidermal cells of sunflower bathed in a cavity which was surrounded by the plasma membrane of the host. After infection of the sunflower cells, an increase in concentration of the host cytoplasm was noted. The haustorium was an elongated ellipsoidal body with tortuose branches which emerged from each end and wove back over the body. The branches seldom came into contact with each other or the body of the haustorium or the surrounding membrane. The possibility of the branches being vestigial or functional is discussed. The haustorial body and branches contained numerous chondriosomes, vesicles, and large electron-dense bodies. These bodies formed in vesicles by coalescence of smaller dense bodies. The chondriosomes were mainly the chondriocont type. In the body of the haustorium a nucleus and an opaque nucleolus with two electron-transparent areas were observed. Encapsulation material was scattered irregularly along the host membrane and was structureless, which suggests that it was waste material. The rest of the cavity was filled with a solution through which interchange between the host and fungus occurred. Active transport from the host protoplasm to the fungus was suggested. No evidence was obtained for cytoplasmic connections between the parasite and the host.