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Root Diseases Induced in Corn by Rhizoctonia solani and Rhizoctonia zeae. Donald R. Sumner, Plant Pathology Department, University of Georgia, Coastal Plain Station, Tifton 31793; D. K. Bell, Plant Pathology Department, University of Georgia, Coastal Plain Station, Tifton 31793. Phytopathology 72:86-91. Accepted for publication 5 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-86.

Numerous fungi isolated from diseased corn roots were pathogenic on corn seedlings and juvenile plants, but field-type symptoms were only produced by cultures of Rhizoctonia solani belonging to anastomosis group two (AG-2). Some isolates of R. solani belonging to anastomosis group four (AG-4) caused severe hypocotyl necrosis, but lesions were rare on lateral, crown, and brace roots, and most isolates were avirulent on corn. Rhizoctonia zeae was less virulent than R. solani AG-2 and AG-4 and caused indistinct buff to light brown lesions on primary and lateral roots. Binucleate Rhizoctonia spp. isolates were not pathogenic. R. solani AG-2 isolates were equally virulent at temperature ranges 821, 1628, and 2034 C, but R. zeae was most virulent at the highest temperature range. R. zeae survived in fallow soil in pots buried in a field for 6 mo. Isolates of R. solani AG-2 from corn were highly virulent on juvenile soybean, snap bean, pole bean, lima bean, southern pea, and cucumber, but only slightly virulent on peanut. Crown, brace, and lateral root rot caused by R. solani AG-2 was found only in corn monoculture or corn grown in rotation with peanut or soybean in irrigated fields in southeast Georgia. Symptoms rarely were observed in nonirrigated corn, and R. solani was not isolated from roots of corn grown in nonirrigated fields.