Light and electron microscope studies on cell wall breakdown in American elm xylem tissues infected with Dutch elm disease

Abstract

Seven years (1970–1977) of comparative light and electron microscope studies show that extensive cell wall disruption and breakdown occur consistently in elm xylem tissues infected by Ceratocystis ulmi (Buism.) C. Moreau. These alterations, noticeable even in incipient infection, can be related to the severity of wilting development and occur in association with the presence of an unbound osmiophilic material containing fine fibrillar material, dense particles of approximately 15 nm, and multilamellate structures. Masses of unbound osmiophilic material in host walls and walled fungal cells with which it is sometimes continuous are highly and exclusively labeled following injection of [6-³H]thymidine.The presence of osmiophilic material in host walls and the interrelation between the two was further established by examining stereoscopic pairs of prints taken at various angles with a goniometer. This type of cell wall breakdown seems difficult to relate to other known types of wood rots. Further discussion on the possible nature and origin of the osmiophilic material is presented.