Characterization and Pathogenicity of Rhizoctonia spp. Isolated from Rice, Soybean, and Other Crops Grown in Rotation with Rice in Texas. R. K. Jones, Extension Plant Pathologist, Department of Plant Pathology and Microbiology, Texas A&M University System, College Station 77843. S. B. Belmar, Former Graduate Student, Department of Plant Pathology and Microbiology, Texas A&M University System, College Station 77843. Plant Dis. 73:1004-1010. Accepted for publication 26 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-1004.

Isolates of Rhizoctonia spp. collected from diseased rice (Oryzae sativa) sheaths were characterized as R. solani AG-1 IA (sasakii form), R. oryzae, and a previously undescribed collection of isolates of R. solani designated AG-UNK that failed to anastomose with AG tester isolates 1 through 8 of R. solani but anastomosed strongly with each other. R. solani AG-1 IA and AG-1 IB (web blight form) were recovered from diseased foliage of soybean (Glycine max) showing characteristic signs and symptoms of aerial blight and web blight, respectively. Isolates of AG-1 IA also were identified from foliage of diseased sorghum (Sorghum bicolor) and corn (Zea mays). The teleomorphs of AG-1 IA, AG-1 IB, and AG-UNK were observed and conformed to the genus Thanatephorus. The teleomorph of R. oryzae was observed and conformed to descriptions of the genus Waitea. A previously undescribed Ceratobasidium sp. was recovered frequently from rice sheaths showing no disease symptoms. In the greenhouse, pathogenicity on young foliage of rice and soybean varied among groups, with isolates of R. solani AG-1 IA and R. solani AG-UNK more virulent on rice and isolates of AG-1 IA, AG-1 IB, and AG-UNK more virulent on soybean. Only isolates of R. solani AG-1 IA significantly reduced rice yields in the field, however.

Keyword(s): banded leaf and sheath blight, sheath blight, sheath spot.