SUSCEPTIBILITY OF SUGAR-BEET AND BEANS TO RHIZOCTONIA-SOLANI AG-2-2-IIIB AND AG-2-2-IV

Isolates of Rhizoctonia solani AG-2-2 from diseased sugar beet, table beet, and three bean species were identified to intraspecific group (I SG) based on growth at 35 degrees C and evaluated for pathogenicity on sugar beet and beans. The ISG for seven isolates from pinto bean, soy bean, and table beet was AG-2-2 IIIB, and for eight isolates from broa d 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. Isolat es of R. solani AG-2-2 IIIB (n = 6) averaged disease ratings of 4.2 an d 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 bea n, 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 a nd soybean were more pathogenic across all bean crops in both seasons ((x) over bar = 4.7, n = 4) compared with the AG-2-2 IIIB isolate from table beet ((x) over bar = 3.6, n = 1) and isolates of AG-2-2 IV ((x) over bar = 3.4, n = 3). Overall, isolates of R. solani AG-2-2 IIIB an d AG-2-2 IV were pathogenic to sugar beet and bean crops, so close rot ation of these crops should be avoided. Also, the host range of our is olates of AG-2-2 was unrelated to ISG.