Phytopathology 1993 | Anastomosis Grouping and Variation in Virulence Among Isolates of Rhizoctonia solani Associated with Dry Bean and Soybean in Ohio and Zaire

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Anastomosis Grouping and Variation in Virulence Among Isolates of Rhizoctonia solani Associated with Dry Bean and Soybean in Ohio and Zaire. N. G. Muyolo,Former graduate student, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691; P. E. Lipps(2), and A. F. Schmitthenner(3). (2)(3)professors, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 83:438-444. Accepted for publication 8 January 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-438.

Anastomosis groupings (AG) of 290 Rhizoctonia solani isolates from diseased dry bean (Phaseolus vulgaris) and soybean (Glycine max) roots and/or hypocotyls and foliage in Ohio (the United States) and Zaire (Africa) were determined. Virulence of 60 isolates, representing 12 isolates each from one of five origin/host/anastomosis-group categories, was studied on dry bean cv. Great Northern and soybean cv. Williams. Variation in virulence was assessed by inoculating roots, hypocotyls, and leaves. Ohio dry bean and soybean hypocotyl/root isolates were AG-2-2 IIIB. Zaire dry bean hypocotyl/root isolates were AG-4, and Zaire dry bean and soybean foliar isolates were AG-1 IB. AG-1 IB isolates caused foliar blight and root and hypocotyl rot in virulence tests. All 24 AG-2-2 IIIB and 11 of 12 AG-4 isolates tested failed to cause foliar symptoms. AG-2-2 IIIB isolates were more virulent on roots than on hypocotyls; AG-4 isolates were more virulent on hypocotyls than on roots. Disease-severity ratings from agar-plate assays and root rot-severity ratings from potted plant assays were correlated (P ≤ 0.05) for dry bean AG-2-2 IIIB (r = 0.70), soybean AG-2-2 IIIB (r = 0.64), and soybean AG-1 IB (r = 0.66) isolates but not for dry bean AG-4 isolates. These results indicate that agar-plate assays represent an acceptable preliminary method of assessing variation in virulence among anastomosis groups.