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The Association of Double-Stranded RNA with Rhizoctonia Decline. Brad Castanho, Department of Plant Pathology, University of California, Davis, CA 95616, Present address of senior author: Monsanto Agricultural Products Co. T1J, 800 N. Lindbergh Blvd., St. Louis, MO 63166; E. E. Butler(2), and R. J. Shepherd(3). (2)(3)Department of Plant Pathology, University of California, Davis, CA 95616. Phytopathology 68:1515-1519. Accepted for publication 1 May 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1515.

The cause of Rhizoctonia decline, a degenerative disease of Rhizoctonia solani was explored. All attempts to isolate and purify a mycovirus or detect viruslike particles (VLPs) in crude or semipurified preparations failed. Nucleic acids were extracted from frozen mycelium and double-stranded ribonucleic acid (dsRNA) was selectively purified. Diseased isolate 189a of R. solani contained three segments of dsRNA with molecular weights approximately equal to 2.2, 1.5, and 1.1 106. Healthy isolate 189HT5 usually contained no detectable dsRNA, but occasionally preparations contained traces of the same-sized segments of dsRNA as in 189a. Elution properties from cellulose columns, insensitivity to DNase, insensitivity to RNase in high ionic strength buffer (2 SSC), but sensitivity in low ionic strength buffer (0.1 SSC), and staining characteristics with ethidium bromide and toluidine blue O, verified that the three segments were dsRNA. The association of dsRNA with disease was shown by converting healthy 189HT5, which contained no detectable dsRNA, to the diseased-type by anastomosis with diseased 189a; the resulting converted 189HT5 mycelium contained the same three segments of dsRNA as in 189a. Twelve additional isolates of R. solani were examined for the presence of dsRNA. Two that were diseased contained unique segments of dsRNA, different from those in isolate 189a, The other ten isolates were healthy and contained no detectable dsRNA.

Additional keywords: Thanatephorus cucumeris, fungal virus, mycovirus, cytoplasmic inheritance.