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Factors Affecting Oospore Germination of Phytophthora megasperma f. sp. medicaginis. Helga Förster, Postdoctoral research associate, Department of Plant Pathology, University of California, Riverside 92521, The senior author is now at Universität Konstanz, Facultät für Biologie, Lehrstuhl für Phytopathologie, 7750 Konstanz, West Germany; O. K. Ribeiro(2), and D. C. Erwin(3). (2)(3)Postdoctoral research associate and professor of plant pathology, respectively, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 73:442-448. Accepted for publication 27 September 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-442.

Oospores of Phytophthora megasperma f. sp. medicaginis were produced on carrot broth and purified of mycelium by digestion in Glusulase® (β-glucuronidase and aryl sulfatase). Incubation of oospores in alfalfa root extract, root exudate, or soil extract at 24 C under blue light (450- 475 nm) increased germination markedly compared to incubation in distilled water. Oospore germination increased with increasing age of the culture from 11 to 50 days. Glucose inhibited germination, but the inhibition could be partially or completely overcome by the addition of acetate or asparagine. Ca2+ at 1 and 10 μg/ml had no effect but at 50 μg/ml inhibited oospore germination. Metabolic inhibitors of RNA and protein synthesis and respiration reduced germination.

Additional keywords: aborted oospores, metabolic inhibitors, root extract, root exudate, soil extract.