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Characterization of Waitea circinata (Rhizoctonia) Isolated from Agricultural Soils in Alaska. R. H. LEINER, University of Alaska Fairbanks, Agricultural and Forestry Experiment Station, 533 East Fireweed, Palmer, AK 99645. D. E. CARLING, University of Alaska Fairbanks, Agricultural and Forestry Experiment Station, 533 East Fireweed, Palmer, AK 99645. Plant Dis. 78:385-388. Accepted for publication 30 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0385.

A Rhizoctonia similar in morphology to R. oryzae and R. zeae was frequently isolated from agricultural soils in south central Alaska during 1983-1990. On potato-dextrose agar, cultures developed white to pale orange mycelium. Sclerotia formed in the agar rather than on the agar surface, were irregular in shape (similar to those of R. oryzae), and dark orange to brown when mature (similar to those of R. zeae). Hyphal diameter averaged 6.1 μm and the number of nuclei per cell averaged 5.4. Radial growth increased from 1.3 mm per 24 hr at 11C to a maximum of 12.8 mm per 24 hr at 30C. Most isolates infected barley seedlings. Calculated as percentage of the noninoculated seedling height, virulence of Alaskan isolates was 49% at 15C and 48% at 25C. Among 87 isolates tested on 2% V8 juice agar or water agar, 7% produced a teleomorph that was identified as Waitea circinata var. circinata.