The purpose of this study was to evaluate the ultrastructural aspects of the host-pathogen relationship between the fungus Sphaerotheca pannosa (Wallr.) Lev. and a susceptible horticultural variety of floribunda rose "Eutin". Attention was given to the penetration of hyphal tubes, and their subsequent development into: haustorial elements in epidermal cells of rose. In addition, changes in the morphology of infected epidermal cells were described. Thin sections of rose leaves infected with S. pannosa were examined in a Hitachi electron microscope, model HS-7, after glutaraldehyde-acrolein fixation, OsO4-uranyl acetate staining, and embedding in Epon plastic. The components of S. pannosa haustoria consisted of a haustorial body with several lobes. The body, and the lobes, were irregular in shape, and were characteristically surrounded by thin haustorial walls. Small amounts of sheath enclosed the haustorial walls, or was found lacking around some haustorial lobes. A slender neck attached the haustorium to the surface hyphal cell, and was considered an extension of that cell, and not the haustorium. At the base of the neck, a septum which contained a central pore, separated the haustorium from the surface hyphal cell, making the haustorium an independent cell. The haustorial protoplasts were similar to hyphal cells on the surface. They contained mitochondria, ribosomes, endoplasmic reticulum, lipid bodies, and vacuoles. Muclei were not detected. Penetration of the epidermal wall of rose by hyphal tubes was accompanied by cellular proliferations on the inner surfaces of the host wall. These proliferations showed layering, and some formed collars around the penetrating tubes. Although the patterns of the proliferations differed from the normal wall layers of the host, one of the layers of the collar exhibited strands of microfibrils. Some haustoria were completely surrounded by cellular proliferations which were similar in electron density to collar material. It was thought that these proliferations were extensions of the collar which formed in response to breakdown of parasitic control. It appeared that the plasma membrane of the host was the sheath membrane, and that it also lined the cavity of the collar.



College and Department

Life Sciences; Plant and Wildlife Sciences



Date Submitted


Document Type





Roses, Diseases and pests; Phytopathogenic fungi; Mildew; Sphaerotheca