The Role of Electrostatics in Spore Liberation by Drechslera turcica

Abstract

Leach (7) proposed an electrostatic mechanism to explain the violent liberation of spores by Drechslera turcica (Pass.) Subram. & Jain. As evidence of this mechanism, he reported that spore release was correlated with voltages across lesions of Northern Leaf Blight in maize leaves. He suggested that spores, sporophores, and surrounding surfaces accumulate charges of like sign, creating a repulsive force that breaks a spore from its sporophore and propels the spore into the air. He cited evidence that free spores of certain fungi carry some excess charge, but he did not evaluate the electrostatic forces caused by this charge. In our paper we examine the origin of the voltages found on lesions by Leach, we evaluate the forces caused by electrostatic charges on spores, and we report attempts to free spores by electrostatic force. Leach (7) found voltages across maize leaves of 1 to 80 mV; these voltages varied in polarity, but their magnitudes increased with increasing relative humidity. He used a Keithley model 155 Null Detector microvoltmeter, connected to two stainless-steel electrodes touching opposite sides of a leaf sandwiched between them. This arrangement allows only the differential voltage between the electrodes 1213