Elucidation of biological protective reaction of Porphyra cells aginst red rot disease and development of disease resistant strain

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1. Isolation and cultivation of red rot disease resistant cell : Red rot disease of Porphyra yezoensis is the most serious disease caused by the fungus Pythium. Disease resistant cell that was not infected with Pythium was found in the dead algal thallus, isolatedand cultivated at 13-15ﾟC on a 12 h dark and 12 h light cycle under the light intensities of120 muE/m^2/s in 1/5 PES medium. After 6 months cultivation, isolated cell grew to thallus. This thallus showed about 2 times strong resistance against the red rot disease compared to that of commercially cultivated Porphyra.2. Investigation of the factors responsible for disease resistance : In the disease resistant thallus, levels of polysaccharide, glycoprotein (extensine), porphyran and 3,6-anhydro-L-garactose related to hardness of cell wall are apparently lower than that of commercially cultivated Porphyra. These results suggest that the lower the contents of wall polysaccharides, the higher the disease resistance.3. The continuity of disease resistance : The disease resistant strain obtained grew in normal shape that is important to the practical use for cultivation. Even in the most suitable environmental conditions that the disease occurs, the resistant strain showed 3 times stronger resistance compared to that of commercially cultivated P.yezoensis.These results obtained above are useful to understand the mechanisms of disease resistance and to develop the disease resistant strain.