| Abstract: | Janczewskia morimotoi Tokida was successfully cultured from spore to reproductive maturity on its host Laurencia nipponica Yamada. The spore penetrates the host without requirement for wound or abrasion sites, growing between host cortical cells and developing a superficial and an endophytic system simultaneously. During the juvenile period, when the parasite is nonpigmented, it differentiates a cortex and the proliferating endophytic filaments enlarge causing a displacement of layers of host cells into the parasitic tissue. Host cells contacted by cells of the parasite exhibit increased wall thickness, cytoplasmic density and vesicle formation. Pit connections between host and parasite cells were rarely observed whereas penetration of host cell walls was seen commonly. As the parasite increases in size, its cells become pigmented evenly throughout the cortex and host cells show less obvious reactions to the parasite. At this same time, the parasite develops branches and reproductive structures. Host plant segments less than 3 cm long failed to grow when infected with spores of the parasite whereas longer segments were not significantly affected by the parasite. In the absence of the host, the parasite cannot complete its development. Although J. morimotoi is well pigmented at maturity, the absence of pigmentation in the juvenile stage, penetration of host cells, and effect on host growth in culture strongly suggest that it is parasitic during at least its early development. |
