Characterization ofRhizoctoniaPopulations Obtained from Sugarbeet Fields with Differing Soil Textures

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Abstract
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 4 sugar beet 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, sugar beet seedling pathogenicity assays and older sugar beet plant pathogenicity assays. Multinucleate and binucleate isolates could not be distinguished by cultural characteristics. Most multinucleate isolates were of 2 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 sugar beet seedlings than were AG-2 isolates; whereas AG-2 isolates were significantly more virulent than were AG-4 isolates on (6-8 wk old) plants. Binucleate isolates were avirulent to weakly virulent on sugar beets in both assays. Most binucleate isolates were obtained from weeds.