Axenic culture of Japanese radish-downy mildew fungus

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Comparing behavior of downy mildew fungus in diseased tissues between two Japanese radish cultivars different in resistance revealed that although growth of the fungus was remarkably different in speed, no clear difference in morphology of intercellular hypha and haustorium was not observed under a light microscope.In order to get axenic culture of this fungus the growth on various media was investigated by using conidia and infected slices as starting materials. While Williams's medium used for successful axenic culture of Puccinia graminis, althogh added various nutrients, was ineffective, Knop's medium promoted the growth of germ-tube. Homogenate of root of Japanese radish inhibited germination of conidium strikingly. However, the homogenate dialized against distilled water and also fraction 5 of it, fractionated by Sephadex G-100 stimulated growth of germ-tube considerably. On various membrances, especially epidermis of scale leave of onion germed conidia formed appressoria and infection hyphae. The infection hyphae grew in intercellular space of the epidermis cell but could not grow on the medium. Many haustorium-like structures were produced on Knop's medium when infected slices were used. Addition of yeast and liver extract, casein hydrate, cod liver oil, minerals and liver to the Knop's medium did not promote formation of the fungal organ. Growth of the fungus was stimulated on the dialized homogenate-medium and also the fraction 5-medium. Numbers of hypha and haustorium-like structure, and length of hypha were increased. Decoction of cell wall- and fluid of intercellular space of root tissue-media also stimulated formation of haustorium-like structure. The former stimulated growth of hypha especially.As mentioned above, this fungus formed all organs which observed in the diseased tissue, on some Japanese radish components-media. Bur the term of growth was short. All efforts to elongate it were not successful.