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Effect of Soil Water Potential on Disease Incidence and Oospore Germination of Pythium aphanidermatum. 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 63:1496-1498. Accepted for publication 4 June 1973. DOI: 10.1094/Phyto-63-1496.

Oospores of Pythium aphanidermatum germinated directly in asparagine-amended soils maintained at soil moisture levels ranging from saturation to 15 bars matric water potential. Percentage oospore germination and germ-tube growth rates were reduced at the lower soil moisture levels. Colonization of alfalfa seeds, sown in soil containing a natural population of 80 viable oospores of P. aphanidermatum/g soil, occurred at all soil moisture levels except 15 bars matric potential. Data indicate that wet soil conditions favor the activity of Pythium by increasing nutrient availability for oospore germination.

Additional keywords: soil moisture, soil-borne fungus, zoospores.