Abstract
The developing process of Plasmodiophora brassicae from the very young plasmodium to the fully matured resting spore was examined by using a scanning electron microscope on the infected cortical cells of turnip and Chinese cabbage. In the early stage of infection, the initial plasmodia in an infected cell were observed as spherical bodies of smooth surfaces with or without strand-like materials and ranged from 3 to 5μm in diameter or as a small cluster mass. The plasmodia developed rapidly. The cut surface of young plasmodia indicated that these developed into a large sponge-like structure. In some cases, the plasmodia consisted of spherical bodies. In a club-cut surface, young plasmodia and vegetative plasmodium were found in the two contiguous cells, respectively. With progressive growth of a plasmodium, a mature resting spore mass was seen in a cell and young plasmodia were noted in its contiguous cell. Young plasmodium or vegetative plasmodium and a resting spore mass were found together in a cell. Immature resting spores were observed to have filamentous connecting materials, while mature spores exhibited spines on their surfaces. At 45-60 days after sowing, the resting spores in an infected cell of club sampled perfectly matured and the cell was filled by innumerable spores. The spore mass did not appear to have an enveloping membrane. In paraffin sections of club tissue, the cell wall of the resting spore was clearly seen.
