Komada’s medium (Komada 1975 Rev. Plant Protec. Res. 8:114-125) was developed as an agar-based selective medium to isolate Fusarium oxysporum from raw soil or infested plant material. Typically, a soil dilution extract or plant material is placed on the agar surface or pushed slightly into the agar. In my experience, other fungi and bacteria can grow under these conditions, presumably by utilizing the soil nutrients or decaying plant material. Thus it is not always possible to obtain pure cultures of F. oxysporum from the surface of Komada’s medium.
I have found that if the soil extract or plant material is overlaid by “flipping” the contents of an additional petri dish of Komada’s medium onto the first, it is then possible to obtain a pure culture of F. oxysporum. The double agar layer plate is incubated at room temperature (25 - 28 C) for 7 - 14 days or until mycelium appears on the surface of the overlying medium and then the fuzzy aerial mycelial growth is transferred to a new plate of any general fungal growth medium (e.g., Czapeks or PDA). It appears that by forcing the hyphae to grow through the overlay, the ability of Komada’s medium to exclude bacteria and other fungi is enhanced dramatically.
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