Development and extension of mycelial cords in soil at different temperatures and moisture contents

Cord systems of Hypholoma fasciculare, Phallus impudicus, Phanerochaete laevis, Phanerochaete velutina and Steccherinum fimbriatum developed progressively in non-sterile soil from advancing mycelial fronts within which linear aggregation of hyphae was followed by lysis of diffuse mycelium. Extension rates of the cord systems were generally linear and mostly increased with temperature from 5 to 20 or 27 °C. Extension rates varied between species and sometimes between strains of the same species. In S. fimbriatum an abrupt change occurred from a slowly extending, highly branched mycelium to a rapidly extending, sparsely branched cord system, which appeared to be triggered by an internal switch rather than by environmental factors. Extension rate was little affected over the range of initial soil matric potentials from − 0·007 MPa (field capacity) to − 0·9 MPa, but extension was hindered above field moisture capacity and only cord systems of H. fasciculare and P. impudicus persisted. Lateral branching decreased as soil matric potential decreased. All strains decayed wood block inocula after 70 d. The minimum temperature at which decay occurred varied between 5° to 15°; decay increased with temperature up to 30° or 27° for all species, but this increase was not always correlated with cord extension rate.