Some Aspects of the Biology of Fusarium oxysporum Schl. in Soil

From either a mycelial or a conidial inoculum the fungus survived in soil as inactive chlamydospores. The level of its soil population at equilibrium was too low to be studied by dilution plating. Plant materials placed on or beneath the surface of inoculated soil were colonized deeply by the fungus, which produced conidia on them. Dispersal of conidia can occur with water movement in soil, and at right angles to, as well as in the direction of, that movement. No evidence was found of dispersal of the fungus in soil by continuous growth, even over continuous stretches of organic matter. This finding was related to the inability of the fungus to colonize those organic materials that were previously colonized by other organisms from the soil, unless its inoculum potential were greatly augmented. The fungus is thus seen to be a pioneer fungus. The strain used here grew outwards a short distance from colonized organic food bases in the soil, leaving in the soil resting spores which could colonize fresh pieces of organic material subsequently added there. The organism could thus spread by discontinuous growth on successively available, fresh, organic materials.