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Effect of Potting Mix Microbial Carrying Capacity on Biological Control of Rhizoctonia Damping-Off of Radish and Rhizoctonia Crown and Root Rot of Poinsettia

November 2001 , Volume 91 , Number  11
Pages  1,116 - 1,123

Matthew S. Krause , Laurence V. Madden , and Harry A. J. Hoitink

Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691

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Accepted 1 August 2001.

Potting mixes prepared with dark, highly decomposed Sphagnum peat, with light, less decomposed Sphagnum peat, or with composted pine bark, all three of which were colonized by indigenous microorganisms, failed to consistently suppress Rhizoctonia damping-off of radish or Rhizoctonia crown and root rot of poinsettia. Inoculation of these mixes with Chryseobacterium gleum (C299R2) and Trichoderma hamatum 382 (T382) significantly reduced the severity of both diseases in the composted pine bark mix in which both biocontrol agents maintained high populations over 90 days. These microorganisms were less effective against damping-off in the light and dark peat mixes, respectively, in which populations of C299R2 declined. In contrast, crown and root rot, a disease that is severe late in the crop, was suppressed in all three types of mixes. High populations of T382 in all three mixes late during the cropping cycle may have contributed to control of this disease.

Additional keywords: Euphorbia pulcherrima , natural suppression , organic amendment , organic matter decomposition , Raphanus sativus , Rhizoctonia solani .

© 2001 The American Phytopathological Society