Perforation and lysis of spores of Cochliobolus sativus and Thielaviopsis basicola in natural soils

Conidia of Cochliobolus sativus and chlamydospores of Thielaviopsis basicola were perforated and lysed when incubated in soil from several locations in Canada. Perforations, ranging in size from 0.2 to 5.0 microns (μ) in diameter, were caused by some member of the soil microbiota. Specific causal agents have not been identified. However, observations by electron microscopy of the surface microflora of spores suggest that holes up to0.5 μ diameter are probably the result of direct penetration of the spore wall by soil bacteria. Larger holes appear to be a result of microbial erosion within annular depressions in the spore surfaces. Perforating agents could be transferred from one fungus to the other.In some of the soils tested, 100% of the spores became perforated and underwent lysis. Pasteurization removed the perforating agent from the soils. A measure of perforating activity was retained in soil that had been fumigated with ‘Telone C’ (mixture containing 85% 1,3-dichloropropene and 15% chloropicrin) at the rate of 30 gal/acre.