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Infection of Wheat Embryos by Pythium Species During Seed Germination and the Influence of Seed Age and Soil Matric Potential. T. F. Hering, Visiting plant pathologist, Department of Plant Pathology, Washington State University, Pullman 99164, Senior lecturer in plant pathology, University of Nottingham, Nottingham, England; R. James Cook(2), W.-h. Tang(3). (2)Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Pullman 99164; (3)Visiting plant pathologist, Department of Plant Pathology, Washington State University, Pullman 99164, Associate professor, Beijing Agricultural University, Beijing, People’s Republic of China. Phytopathology 77:1104-1108. Accepted for publication 5 February 1987. 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, 1987. DOI: 10.1094/Phyto-77-1104.

Pythium spp. (mainly P. irregulare and P. ultimum var. sporangiiferum) were isolated from the scutellum region of 30–55% of random winter wheat seedlings dug 3 wk after sowing (just emerged) from five sites, yet stand establishment was not a problem at any of the sites. The presence of Pythium spp. in the scutellum region was traced to embryo infections that occurred during the first 2 days after sowing. In pot experiments, infection of wheat embryos by Pythium spp. at 2 days after planting (20 C) occurred maximally (45%) at –0.1 bar matric potential and was essentially prevented at –0.4 to –1.2 bar. Seedlings produced from seeds pregerminated for 48 hr on moist filter paper in petri dishes then transplanted into Pythium-infested soil showed no evidence of leaf distortion or stunting and were identical to those produced from seeds sown directly into Pythium-free (pasteurized) soil. The older the seed (e.g., 3–7 yr old), the greater the incidence of seed decay caused by Pythium spp. An exception was a 7-yr-old seedlot of cultivar Daws stored at a constant 5 C, which emerged 87.5% in Pythium-infested soil, in contrast to a portion of the same seedlot stored at the normal fluctuating summer/winter temperatures, which emerged 35% in Pythium-infested soil. Both seedlots emerged 100% in Pythium-free soil. Treatments of the old seed with carboxin and thiram, captan, or metalaxyl improved emergence, but the seedlings were still smaller than those produced from new seed.

Additional keywords: soilborne pathogen.