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Germination In Vivo of Pythium aphanidermatum Oospores and Sporangia. M. E. Stanghellini, Associate Professor, Department of Plant Pathology, University of Arizona, Tucson 85721; T. J. Burr, Graduate Research Assistant, Department of Plant Pathology, University of Arizona, Tucson 85721. Phytopathology 63:1493-1496. Accepted for publication 4 June 1973. DOI: 10.1094/Phyto-63-1493.

Oospores of Pythium aphanidermatum were capable of either direct (production of germ tubes) or indirect (production of zoospores) germination in field soil, depending on the presence or absence of an exogenous source of nutrients. In the presence of nutrients, oospores germinated exclusively by a germ tube which continued elongation and either terminated in a sporangium prior to lysis or penetrated the host directly. Zoospore production from germinating oospores in soil occurred in the absence of exogenous nutrients and was restricted to the surface water of saturated soils. Sporangia, formed in soil prior to germ-tube lysis, germinated directly upon addition of a substrate to moist soil but did not persist for more than 2 days in air-dry soil. Oospores and not zoospores apparently are the major root-infecting units in field soil.

Additional keywords: soil-borne fungus, fungistasis.