Comparative studies were carried out on the cultural character and pathogenicity of isolates of the causal fungus of the red wasting disease, obtained from various culture grounds for Porphyra in Japan. The isolates can be separated into two types on the basis of their nutritional behavior and growth type: one type, named “Seinan type”, requires specific factors for their growth and these isolates show conidium type growth in the synthetic liquid medium containing sucrose and xylan as the carbon source; and the other, named “Tohoku type”, does not require any specific growth factors and grows vigorously with a mycelium type in the medium.
“Seinan type” isolates are much stronger in their pathogenicity than the “Tohoku type” isolates. However, whether these two types of isolates are recognized as a “Race” or not, is a subject for future study.
The growth of hyphae in the Nori tissue is more closely correlated with the metabolic activity (peroxidase activity) of frond tissue rather than nutritive conditions or age of the fronds. The growth speed of hyphae into the tissue of low metabolic activity decreases rapidly in the order of several days after inoculation, but in the tissue of high activity, the growth of hyphae continues vigorously over a long period of time.