Characteristics of Rhizoctonia solani and Binucleate Rhizoctonia Species Causing Foliar Blight and Root Rot on Table Beets in New York State. GILBERTO OLAYA, Graduate Research Assistant, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456-0462. GEORGE S. ABAWI, Professor, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456-0462. Plant Dis. 78:800-804. Accepted for publication 2 May 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0800.

A total of 107 isolates of Rhizoctonia solani and binucleate Rhizoctonia species were collected over a 2-yr period from naturally infected roots, petioles, and leaf tissues of table beets (Beta vulgaris) as well as directly from hymenia of the teleomorph, Thanatephorus cucumeris, on petiole and crown tissues. Ninety-eight of these isolates were found to be multinucleate, with diagnostic characteristics of R. solani (T. cucumeris), while the remaining nine isolates originating only from root tissues were binucleate Rhizoctonia species. About 88% of the R. solani isolates belonged to anastomosis group 2-2 (AG-2-2), and the remainder were either AG-5, AG-4, or AG-2-I. Binucleate isolates had a slower growth rate on PDA at 28 C than multinucleate isolates. Although isolates of AG-2-2 originated from different tissues, their average growth rate on PDA and colony characteristics were similar. The AG-2-2 isolates from roots and petioles were highly to moderately virulent to leaves and were highly virulent to root tissues of table beets. The AG-4 and AG-5 isolates were low to moderately virulent to leaves but highly virulent to roots. The binucleate isolates were weakly virulent to both leaves and roots. There was no apparent correlation between the growth rate of the R. solani isolates and their virulence to either roots or leaves of table beets. A widespread strain of R. solani and its teleomorph are causing both the foliar blight and the root rot diseases of table beets in central New York.