Susceptibility of Sugar Beet and Beans to Rhizoctonia solani AG-2-2 IIIB and AG-2-2 IV. Cheryl Ann Engelkes, Former Research Assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Carol E. Windels, Associate Professor of Plant Pathology, Northwest Experiment Station, University of Minnesota, Crookston 56716. Plant Dis. 80:1413-1417. Accepted for publication 29 September 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1413.

Isolates of Rhizoctonia solani AG-2-2 from diseased sugar beet, table beet, and three bean species were identified to intraspecific group (ISG) based on growth at 350C and evaluated for pathogenicity on sugar beet and beans. The ISG for seven isolates from pinto bean, soybean, and table beet was AG-2-2 IIIB, and for eight isolates from broad bean and sugar beet was AG-2-2 IV. Severity of Rhizoctonia root and crown rot on sugar beet (0 to 7 scale) differed in two seasons. Isolates of R. solani AG-2-2 IIIB (n = 6) averaged disease ratings of 4.2 and 5.3 in 1988 and 1989, respectively; and isolates of AG-2-2 IV (n = 8) averaged 2.0 and 4.0 in 1988 and 1989, respectively. Isolates of R. solani AG-2-2 IIIB (n = 5) and AG-2-2 IV (n = 3) evaluated on navy bean, pinto bean, soybean, and broad bean caused stem rot (1 to 5 scale) on all bean crops. Isolates of R. solani AG-2-2 IIIB from pinto bean and soybean were more pathogenic across all bean crops in both seasons (x = 4.7, n = 4) compared with the AG-2-2 IIIB isolate from table beet (x = 3.6, n = 1) and isolates of AG-2-2 IV (x = 3.4, n = 3). Overall, isolates of R. solani AG-2-2 IIIB and AG-2-2 IV were pathogenic to sugar beet and bean crops, so close rotation of these crops should be avoided. Also, the host range of our isolates of AG-2-2 was unrelated to ISG.