3.1.2 Olpidiopsis disease 

The disease shown in Figure 10 has been reported in China, Korea and Japan. Initially thought to be a chytrid, Olpidiopsis is actually an ob­ligate endoparasitic oomycete, infecting many different species of Pyropia. Symptoms (seen in Figure 10) are characterised by distinct bleached portions on blades at the initial stages and the development of greenish lesions upon spreading of the disease. The infection process starts when encysted zoospores of Olpidiopsis attach to the surface of Pyropia and produce thin germ tubes that penetrate the cell walls of the host. After entering the host cell, Olpidiopsis forms spherical multinucleate thalli, which develop into fully grown zoosporangia within the next two days. Zoospores escape through a discharge tube, which forms at the final developmental stage of the zoosporangium. Again, decay of tissue in infected areas quickly promotes the death of the whole plant.

Figure 10 Macroscopic (a) and microscopic (b,c) Olpidiopsis infection symptoms observed on Pyropia blades. (a) decaying greenish areas. (b) Enlarged picture, each green cell contains one multinucleate Olpidiopsis thallus, scale bar 50 μm.

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Two images, showing Pyropia holes in the frond due to Olpidiopsis infection are clearly visible. Microscope image shows cellular level, with infected cells in green

Figure 10 Macroscopic (a) and microscopic (b,c) Olpidiopsis infection symptoms observed on Pyropia blades. (a) decaying greenish areas. (...