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The Interaction of Fusarium oxysporum and Rhizoctonia solani in Causing Root Rot of Soybeans. L. E. Datnoff, USDA-ARS, Foreign Disease-Weed Science Research Unit, Fort Detrick, Bldg. 1301, Frederick, MD 21701, Present address: University of Florida-IFAS, Everglades Research and Education Center, P.O. Box 8003, Belle Glade 33430; J. B. Sinclair, Department of Plant Pathology, University of Illinois, Urbana-Champaign, 1102 S. Goodwin Ave. 61801. Phytopathology 78:771-777. Accepted for publication 21 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-771.

In the growth chamber, disease severity and incidence of soybean roots were greater in plants inoculated with Fusarium oxysporum and Rhizoctonia solani than with either alone. Root infection and recovery of R. solani were lower in the presence of F. oxysporum, and greater for F. oxysporum in the presence of R. solani than for either pathogen alone. In the field, root infection did not differ significantly (P = 0.05) when plants were inoculated with both fungi or by R. solani alone. Disease-severity ratings for plants in plots infested with the pathogen mixture also were greater than with either pathogen alone up to 36 days after planting. Plants inoculated with both fungi or with R. solani alone were shorter than plants uninoculated or inoculated with F. oxysporum. The interaction of F. oxysporum and R. solani in causing a root rot of soybean appears to be additive.