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Influence of Soil Temperature on Rhizoctonia Root Rot (R. solani AG-8 and R. oryzae) of Winter Wheat. R. W. Smiley, Oregon State University, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton 97801; W. Uddin, Oregon State University, Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton 97801. Phytopathology 83:777-785. Accepted for publication 1 March 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-777.

Rhizoctonia solani AG-8 and R. oryzae are associated with Rhizoctonia root rot of cereals in the northwestern United States. These pathogens were evaluated in the greenhouse and field for effects on disease severity and growth, development, and yield of winter wheat. Experiments in the greenhouse were performed either with pasteurized soil mixture or intact cores of natural soil collected from the field. Soil temperatures were controlled at diurnal cycles of 27/16, 23/11, or 19/6 C, or experiments were performed at ambient temperatures of 28/15 C. Inocula of the Rhizoctonia species were also placed in a band below winter wheat seed in the field. R. solani caused moderate to severe disease and reduced plant growth and development in all six greenhouse and field tests. R. solani in natural soil caused more severe root rot at low than at high temperature. R. oryzae caused slight to moderate root rot in natural soil and severe root rot in pasteurized soil at high temperature, but never significantly (P < 0.05) suppressed plant growth or development. Grain yields for winter wheat growing in soil infested with R. solani, R. oryzae, or neither pathogen were 624, 8,724, and 9,444 kg/ha, respectively, during one field test. The yield component most closely associated with root rot during both field seasons was tiller development. We conclude that R. solani AG-8 is the principal incitant of Rhizoctonia root rot on winter wheat in the Pacific Northwest.

Additional keywords: barley, Hordeum vulgare, peas, Pisum sativum, Thanatephorus cucumeris, Triticum aestivum, Waitea circinata.