Reaction of Winter Wheat to Pythium Snow Rot. P. E. Lipps, Research Assistant, Department of Plant Pathology, Washington State University, Pullman 99164. G. W. Bruehl, Professor, Department of Plant Pathology, Washington State University, Pullman 99164. Plant Dis. 64:555-558. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-555.

In laboratory tests with Pythium iwayamai, small wheat plants (three to four leaves, no tillers) were more resistant to snow rot than were larger plants (seven to nine tillers per plant). In a search for sources of resistance, only six of 77 wheats inoculated with P. iwayamai gave 50% or greater survival after incubation for 63–77 days under flooded conditions at 0.5 C. The most resistant line, Sel. 7439, averaged 66% survival. In early seeded field trials with natural inoculum, no wheat tested had sufficient resistance in the field to provide > 50% survival. Resistance to snow rot is not related to resistance to snow mold and is different from winterhardiness. Large plants obtained by early seeding survive snow mold better than small plants from late seedings, and small plants obtained by late seeding survive snow rot better than large plants. Although the breeding of one cultivar with resistance to both diseases may be possible if a wheat such as CI 14106 is used as a resistant parent, the contrasting response to seeding dates makes cultural control more difficult.