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Rhizoctonia Species and Anastomosis Groups Causing Root Rot of Wheat and Barley in the Pacific Northwest. A. Ogoshi, Professor of plant pathology, Hokkaido University, Sapporo, Japan; R. J. Cook(2), and E. N. Bassett(3). (2)Research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Washington State University, Pullman 99164; (3)Former associate in research, Department of Plant Pathology, Washington State University, Pullman 99164. Phytopathology 80:784-788. Accepted for publication 1 February 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/Phyto-80-784.

Of 104 isolates of Rhizoctonia solani from roots or rhizosphere soil of wheat or barley plants representing 45 fields in Idaho, Oregon, and Washington, 42% (representing 14 of the 45 fields) were AG-8. The rest were AG-3 (four), AG-4 (34), AG-5 (one), AG-9 (one), and a possible newly recognized AG-10 (20). AG-8 made up 67% of the isolates of R. solani from plants, whereas AG-3, AG-4, AG-9, and AG-10 made up 85% of those from soil. R. oryzae (anastomosis group WAG-O) was recovered from 17 fields; 58% of the isolates were from roots and 42% were from soil. The binucleate isolates were AG-CI (five), AG-D (five), AG-E (18), AG-H (four), and AG-K (eight). At 10 C, isolates of AG-8 were highly pathogenic and those of R. oryzae were nonpathogenic or mildly pathogenic to wheat and barley. At 20 C, isolates of R. oryzae were moderately pathogenic, whereas those of R. solani AG-8 were mildly pathogenic to wheat and barley. Isolates of R. solani AG-4 and AG-5 and R. oryzae from Arkansas (AR) and Japan (Jpn) (both from rice) were nonpathogenic or mildly pathogenic at both 10 and 20 C. The optimal water potential for colony growth of R. solani AG-4 and AG-8, R. oryzae from rice (AR and Jpn), and R. oryzae from wheat or barley from the Pacific Northwest (PNW) was ?0.2 to ?0.6 MPa at temperatures between 15 and 35 C. Conversely, the optimal temperature for growth was about 25 C for R. solani AG-4 and AG-8, 28?30 C for R. oryzae from wheat or barley (PNW), and 32?35 C for R. oryzae from rice (AR and Jpn). Apparently, R. solani AG-8 and R. oryzae both are involved in Rhizoctonia root rot of wheat and barley in the Pacific Northwest. Although R. oryzae requires a higher temperature than R. solani AG-8 to cause root rot of wheat and barley, these strains, compared with those of the same anastomosis group from rice, may represent a ?low temperature? ecotype of this species.

Additional keywords: soilborne pathogen, root disease, bare-patch.