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Storage and Use of Phytophthora megasperma var. sojae Oospores as Inoculum. D. R. Kittle, Graduate student and research assistant, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Department of Plant Pathology, and University of Illinois, Urbana, IL 61801; L. E. Gray, research plant pathologist and associate professor, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, Department of Plant Pathology, and University of Illinois, Urbana, IL 61801. Phytopathology 69:821-823. Accepted for publication 20 February 1979. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1979. DOI: 10.1094/Phyto-69-821.

Chilling (– 7 C), heating (40 C), and sonication were evaluated as methods of freeing oospores of Phytophthora megasperma var. sojae from viable mycelia. Hosts (Glycine max) were grown in soil infested with 1,000 oospores per gram (OPG) of soil from each treatment. Percentages of plants infected were 100, 100, 93, and 69 for untreated oospores, chilled, sonicated, and heated, respectively. When chilled suspensions were used to infest soil at 0, 10, 100, 250, 500, and 1,000 OPG, percentages of soybean seedlings infected were 0, 27, 65, 81, 98, and 100, respectively. Chilled oospores were evaluated for pathogenicity at 2-wk intervals from 0 to 6 wk of storage. Relative root reduction of inoculated seedlings at 1,000 OPG were 37.8, 30.8, 22.3, and 10.8 for 0, 2, 4, and 6 wk, respectively.