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The Biology of Cylindrocladium scoparium in Wisconsin Forest Tree Nurseries. Walter G. Thies, Former Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; Robert F. Patton, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 60:1662-1668. Accepted for publication 19 June 1970. DOI: 10.1094/Phyto-60-1662.

The primary propagule of Cylindrocladium scoparium in nursery soils was determined to be the microsclerotium. Microsclerotia apparently were incapable of repeated germination. Viability in soil samples was greatly reduced by drying. Viable microsclerotia were recovered in relatively high numbers from soil that had remained in clean fallow for 7 years. They were present in varying amounts in all blocks of a Wisconsin nursery, but were recovered only occasionally and in small numbers from soil within windbreaks in the nursery. The fungus was not isolated from soil of the forest adjacent to the nursery. A vertical gradient existed in nursery soil, the microsclerotial population increasing from the surface down to the plowline at about the 15-cm level. No microsclerotia were detected below the plowline. The fungus did not grow through nonsterile soil, nor did it move from one seedling to another by root contacts. The fungus was probably introduced on roots of infected seedlings in internursery stock transfers. Once introduced, it increased in infected roots and was distributed throughout the nursery by cultural operations. The microsclerotial population increased in soil when soybean was used as a cover crop, but was lowest in soil in which corn, grown as a cover crop, was incorporated.