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Characterization of Rhizoctonia Populations Obtained from Sugarbeet Fields with Differing Soil Textures. L. J. Herr, Professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; D. L. Roberts, former research assistant, Department of Plant Pathology, The Ohio State University, Columbus 43210. Phytopathology 70:476-480. Accepted for publication 15 November 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-476.

Representative Rhizoctonia cultures were selected from populations isolated from soil and from weed hosts in areas of apparently healthy and crown- and root-rot diseased beets. The four sugarbeet fields assayed during the summer and fall of 1976 differed in soil textures (sandy loam, fine sandy loam, silt loam, and silty clay loam). The selected isolates were distinguished by cultural characteristics, anastomosis grouping, numbers of nuclei, sugarbeet seedling pathogenicity assays, and older sugarbeet plant pathogenicity assays. Multinucleate and binucleate isolates could not be distinguished by cultural characteristics. Most multinucleate isolates were of two anastomosis groups, AG-2 and AG-4. In fine textured soils AG-2 isolates predominated, whereas in the coarser textured soils numbers of AG-2 and AG-4 isolates were nearly equal in one soil and AG-4 isolates predominated in the other. AG-4 isolates were significantly more virulent to sugarbeet seedlings than were AG-2 isolates; whereas AG-2 isolates were significantly more virulent than were AG-4 isolates on (6- to 8-wk-old) plants. Binucleate isolates were avirulent to weakly virulent on sugarbeets in both assays. Most binucleate isolates were obtained from weeds.