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

From either a mycelial or a conidial inoculum the fungus survivedin soil as inactive chlamydospores. The level of its soil populationat equilibrium was too low to be studied by dilution plating.Plant materials placed on or beneath the surface of inoculatedsoil were colonized deeply by the fungus, which produced conidiaon them. Dispersal of conidia can occur with water movementin soil, and at right angles to, as well as in the directionof, that movement. No evidence was found of dispersal of thefungus in soil by continuous growth, even over continuous stretchesof organic matter. This finding was related to the inabilityof the fungus to colonize those organic materials that werepreviously colonized by other organisms from the soil, unlessits inoculum potential were greatly augmented. The fungus isthus seen to be a pioneer fungus. The strain used here grewoutwards a short distance from colonized organic food basesin the soil, leaving in the soil resting spores which couldcolonize fresh pieces of organic material subsequently addedthere. The organism could thus spread by discontinuous growthon successively available, fresh, organic materials.