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Propagule Nature and Density of Pythium aphanidermatum in Field Soil. T. J. Burr, Graduate Research Assistant, Department of Plant Pathology, University of Arizona, Tucson 85721; M. E. Stanghellini, Associate Professor, Department of Plant Pathology, University of Arizona, Tucson 85721. Phytopathology 63:1499-1501. Accepted for publication 4 June 1973. DOI: 10.1094/Phyto-63-1499.

Oospores were the sole survival structure of Pythium aphanidermatum in naturally infested field soil. Population counts determined on a species-specific isolation medium from naturally infested soils of various types ranged from 10-250 oospores/g soil. Enzymatic degradation of colonized organic matter apparently resulted in liberation of dormant oospores which have an exogenous nutrient requirement for germination. No evidence was obtained for the presence of a constitutively dormant oospore population in naturally infested soils.

Additional keywords: soil-borne fungus, survival structure, population, selective medium.