Abstract
The ultrastructure of root of mulberry trees infected with violet root rot fungus (Helicobasidium mompa Tanaka) was observed.
Infection cushion of this fungus was formed on roots, and the penetration into young root tissues occurred through the cell suture of cork layer of root. As soon as hyphae reached the cortex, each hypha elongated in all direction invading cortex cells. Abundant hyphae were observed in the cortex surrounding the xylem and caused severe degeneration of cortex cells. Some of the hyphae elongated into vessels through a pit. The cellulose microfibrils of cell wall of the invaded cells were irregularly arranged, showing the degeneration pattern. The nucleoplasm appeared granular. The plasmolysis occured in all the invaded cells and plasma membrane was cut into small pieces. The degeneration of pectic substances present in the middle lamella resulted in the intercellular spaces.
The hyphal cells of infection cushion were irregular in shape. Those in the mergin of infection cushion were larger, if compared with those of the central part of infection cushion. Finely granular substances, generally called cementing material, appeared to fill the spaces between the adjoining hyphae. The hyphal cells were rich in glycogenlike granules and organelles. A single pore was observed in a hyphal septum. Woronin body enveloped by a unit membrane was present near the septal pore.
