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Evidence for an Electrostatic Mechanism in Spore Discharge by Drechslera turcica. C. M. Leach, Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; Phytopathology 70:206-213. Accepted for publication 5 September 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-206.

Violent discharge of conidia by Drechslera turcica was studied visually and photographically in a specially designed Tyndall apparatus. Conidia were propelled into the air approximately at right angles to the sporulating lesion regardless of the orientation of the surface to gravity. When several spores were discharged simultaneously, their initial trajectories were parallel. Slight vibration of specimens caused synchronized release of conidia with trajectories identical to those of spores released in the absence of vibrations. Conidia discharged near two needle electrodes (400 V, DC) 10 mm apart consistently were attracted to the positive electrode whether liberated in response to vibration or in response to humidity changes. Conidia discharged near electrodes charged with an alternating current (115 V, 60 Hz) followed sinusoidal trajectories. When the potentials of sporulating specimens were artificially increased by applying negative voltages from 0 to 1,800, velocity of discharge increased with increase in voltage. The most convincing evidence for an electrostatic mechanism resulted from experiments on the electrical neutralization of sporulating lesions. Application of positive ions from a piezo-electric ion generator to the negatively charged sporulating lesion, stopped spore discharge. The results of these studies support the existence of an electrostatic mechanism for the violent discharge of conidia by D. turcica. Preliminary visual observations also were made on spore discharge by several other Fungi Imperfecti (Drechslera maydis, Stemphylium botryosum, and Pyricularia oryzae). All discharged conidia violently and the flight paths of liberated spores resembled those of D. turcica.