An Electrostatic Theory to Explain Violent Spore Liberation by Drechslera Turcica and Other Fungi

SUMMARY

Measurement of voltages associated with sporulating maize leaf lesions revealed electrical charges that appeared to relate to violent liberation of conidia. Under precisely controlled conditions (relative humidity, temperature, light and air flow) maize leaf lesions became electrically charged in saturated air. Violent release of conidia triggered by either decreasing the relative humidity (RH), increasing the RH or exposing specimens to red- infrared radiation, was accompanied by significant voltage changes. Similar electrical changes were associated with healthy maize leaves growing under greenhouse conditions. On the basis of these experiments and other evidence, it is proposed that violent liberation of spores involves an exogenous surface electrical phenomenon whereby spores, sporophores and surrounding surfaces become charged (like charges) during periods of high humidity and this initiates an electrostatic repulsion between spore and sporophore. Lowering of the RH causes the charge to become static and also causes a weakening of the juncture between spore and sporophore. When the anatomical bond is sufficiently weakened the juncture breaks and the electrostatic force propels the spore into the air. Surface charges appear to originate mainly from the surface electrical phenomena associated with evaporation and condensation of water, and also under certain conditions from rain. An exogenous electrostatic mechanism should apply to all fungi having exposed nonmucilaginous spores (conidia, sporangia and basidiospores) borne on sporophores with a constriction between spore and sporophore, or between spores when in chains.